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Re: [RFC PATCH] always probe UART HW when options are not specified

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  Re: [RFC PATCH] always probe UART HW when options are not specified Sebastian Frias <sf84@laposte.net> - 2016-01-11 16:10 +0100
    Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-11 17:20 +0100
      Re: [RFC PATCH] always probe UART HW when options are not specified Sebastian Frias <sf84@laposte.net> - 2016-01-11 19:00 +0100
        Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-11 20:10 +0100
          Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-11 21:00 +0100
            Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-11 21:30 +0100
          Re: [RFC PATCH] always probe UART HW when options are not specified Mason <slash.tmp@free.fr> - 2016-01-12 10:40 +0100
            Re: [RFC PATCH] always probe UART HW when options are not specified Sebastian Frias <sf84@laposte.net> - 2016-01-12 15:30 +0100
              Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-12 20:50 +0100
                Re: [RFC PATCH] always probe UART HW when options are not specified Mason <slash.tmp@free.fr> - 2016-01-12 23:30 +0100
                  Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-12 23:50 +0100
                Re: [RFC PATCH] always probe UART HW when options are not specified Sebastian Frias <sf84@laposte.net> - 2016-01-13 12:20 +0100
                  Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-13 17:40 +0100
          Re: [RFC PATCH] always probe UART HW when options are not specified Sebastian Frias <sf84@laposte.net> - 2016-01-12 15:20 +0100
            Re: [RFC PATCH] always probe UART HW when options are not specified Peter Hurley <peter@hurleysoftware.com> - 2016-01-12 22:20 +0100

#1306376 — Re: [RFC PATCH] always probe UART HW when options are not specified

On 12/22/2015 06:56 PM, Sebastian Frias wrote:
> On 12/21/2015 05:50 PM, Sebastian Frias wrote:
>>> You need to use the format documented in
>>> Documentation/kernel-parameters.text:
>>>
>>>     console=    [KNL] Output console device and options.
>>>
>>>         uart[8250],io,<addr>[,options]
>>>         uart[8250],mmio,<addr>[,options]
>>>         uart[8250],mmio16,<addr>[,options]
>>>         uart[8250],mmio32,<addr>[,options]
>>>         uart[8250],0x<addr>[,options]
>>>             Start an early, polled-mode console on the 8250/16550
>>>             UART at the specified I/O port or MMIO address,
>>>             switching to the matching ttyS device later.
>>>             MMIO inter-register address stride is either 8-bit
>>>             (mmio), 16-bit (mmio16), or 32-bit (mmio32).
>>>             If none of [io|mmio|mmio16|mmio32], <addr> is assumed
>>>             to be equivalent to 'mmio'. 'options' are specified in
>>>             the same format described for ttyS above; if unspecified,
>>>             the h/w is not re-initialized.
>>>
>>> The iotype and the uart address are not options.
>>
>> Do you mean they are mandatory?
>> How do they relate to the keys present on the DT? Because the device is
>> already described in the DT:
>>
>>          uart: serial@10700 {
>>              compatible = "ralink,rt2880-uart";
>>              reg = <0x10700 0x30>;
>>              interrupts = <1 IRQ_TYPE_LEVEL_HIGH>;
>>              clock-frequency = <7372800>;
>>              reg-shift = <2>;
>>          };
>>
>> Are we supposed to duplicate such information (ie: addr) in the
>> commandline as well?
>>
>
> By the way, I tried using the following command line
> 'console=uart,mmio32,0x10700,115200n8r mem=256M earlyprintk debug
> ignore_loglevel' but I think I'm still missing something regarding this,
> because it does not work, here's a log of Linux 4.1.13+:
>
>
> 1: [arch/arm/kernel/setup.c:932] setup_arch(): r1 = 0xf34, r2 =
> 0x803b3b50, cmdline ''
> 1: [arch/arm/kernel/devtree.c:195] arch_get_next_mach(): infoBegin
> 0xc024faac, mdesc 0xc024faac
> 1: [arch/arm/kernel/devtree.c:195] arch_get_next_mach(): infoBegin
> 0xc024faac, mdesc 0xc024fb14
> 1: [drivers/of/fdt.c:106] of_fdt_is_compatible(): sigma,tango4 vs
> sigma,vantage-1172
> 1: [arch/arm/kernel/devtree.c:195] arch_get_next_mach(): infoBegin
> 0xc024faac, mdesc 0xc024fb7c
> 1: [drivers/of/fdt.c:749] of_flat_dt_match_machine(): Machine model:
> Sigma Designs SMP8758 Vantage-1172 Rev E1
> 1: [arch/arm/kernel/devtree.c:256] setup_machine_fdt(): about to call
> early_init_dt_scan_nodes
> 1: [drivers/of/fdt.c:1057] early_init_dt_scan_nodes(): bootcmdline ''
> 1: [drivers/of/fdt.c:1062] early_init_dt_scan_nodes(): bootcmdline after
> of_scan_flat_dt 'console=uart,mmio32,0x10700,115200n8r mem=256M
> earlyprintk debug ignore_loglevel'
> 1: [arch/arm/kernel/setup.c:946] setup_arch(): using DT at r2
> 1: [arch/arm/kernel/setup.c:949] setup_arch(): machine name Sigma Tango DT
> 1: [arch/arm/kernel/setup.c:967] setup_arch(): before parse_early_param
> 1: [init/main.c:468] parse_early_param(): bootcmdline
> 'console=uart,mmio32,0x10700,115200n8r mem=256M earlyprintk debug
> ignore_loglevel'
> 1: [init/main.c:473] parse_early_param(): mark
> 1: [init/main.c:428] do_early_param(): enter with: 'console'
> 'uart,mmio32,0x10700,115200n8r'
> 1: [init/main.c:446] do_early_param(): 'earlycon', setup_func 0xc024b868
> 1: [drivers/tty/serial/earlycon.c:214] param_setup_earlycon():
> 'uart,mmio32,0x10700,115200n8r'
> 1: [drivers/tty/serial/earlycon.c:181] setup_earlycon():
> 'uart,mmio32,0x10700,115200n8r'
> 1: [drivers/tty/serial/earlycon.c:132] register_earlycon():
> 'mmio32,0x10700,115200n8r' 'uart'
> 1: [drivers/tty/serial/earlycon.c:86] parse_options():
> 'mmio32,0x10700,115200n8r'
> 1: [drivers/tty/serial/earlycon.c:91] parse_options(): addr 0x00010700,
> options '115200n8r'
> 1: [drivers/tty/serial/earlycon.c:117] parse_options(): Early serial
> console at MMIO32 0x10700 (options '115200n8r')
> 1: [drivers/tty/serial/earlycon.c:138] register_earlycon(): '(null)'
> 1: [drivers/tty/serial/earlycon.c:62] earlycon_map(): paddr 0x00010700
> size 64
>
> As you can see, now that the options are more complete, the match for
> "earlycon" succeeds, but it does not work, the last log is in
> earlycon_map() function.
> When using just "console=uart", the "earlycon" match will fail but a
> match for "earlyprink" will succeed. That one will hook printch() from
> the arch-dependent code to a somewhat simpler 'earlycon'
> (arch/arm/kernel/early_printk.c).
>
> I think the code is the same on mainline.
>
> Also, regarding my previous question about using a HW described in DT
> for earlycon, I noticed there's a of_setup_earlycon() in
> drivers/tty/serial/earlycon.c but that is hooked to
> drivers/of/fdt.c:setup_of_earlycon() which is not called. I do have
> CONFIG_SERIAL_EARLYCON=y.
>
> I also have a similar issue (ie: get blocked right after the call to
> earlycon_map function, log is obviously different from above) if attempt
> to use of_setup_earlycon.
> My DT has roughly:
>
>      aliases {
>          serial0 = &uart;
>      };
>
>      chosen {
>             bootargs = "earlycon console mem=256M earlyprintk debug
> ignore_loglevel";
>             stdout-path = "serial0:115200n8";
>      };
>
>      uart: serial@10700 {
>          compatible = "ralink,rt2880-uart";
>          reg = <0x10700 0x30>;
>          interrupts = <1 IRQ_TYPE_LEVEL_HIGH>;
>          clock-frequency = <7372800>;
>          reg-shift = <2>;
>      };
>
>
> and then I hack drivers/tty/serial/8250/8250_early.c by adding:
>
>      OF_EARLYCON_DECLARE(rt2880, "ralink,rt2880-uart",
> early_serial8250_setup);
>
> at the end of the file, trying to mimic commit
> d05f15707bb7659d2b863fafa1a918f286d74a63
>
> I'm still trying to figure out the right bootargs, so that's why both
> "earlycon" and "console" are there. Suggestions welcome.
>

Does anybody has comments or suggestions regarding this thread and the 
issue above?

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#1306459

On 01/11/2016 07:07 AM, Sebastian Frias wrote:
> On 12/22/2015 06:56 PM, Sebastian Frias wrote:
>> On 12/21/2015 05:50 PM, Sebastian Frias wrote:
>>>> You need to use the format documented in
>>>> Documentation/kernel-parameters.text:
>>>>
>>>>     console=    [KNL] Output console device and options.
>>>>
>>>>         uart[8250],io,<addr>[,options]
>>>>         uart[8250],mmio,<addr>[,options]
>>>>         uart[8250],mmio16,<addr>[,options]
>>>>         uart[8250],mmio32,<addr>[,options]
>>>>         uart[8250],0x<addr>[,options]
>>>>             Start an early, polled-mode console on the 8250/16550
>>>>             UART at the specified I/O port or MMIO address,
>>>>             switching to the matching ttyS device later.
>>>>             MMIO inter-register address stride is either 8-bit
>>>>             (mmio), 16-bit (mmio16), or 32-bit (mmio32).
>>>>             If none of [io|mmio|mmio16|mmio32], <addr> is assumed
>>>>             to be equivalent to 'mmio'. 'options' are specified in
>>>>             the same format described for ttyS above; if unspecified,
>>>>             the h/w is not re-initialized.
>>>>
>>>> The iotype and the uart address are not options.
>>>
>>> Do you mean they are mandatory?
>>> How do they relate to the keys present on the DT? Because the device is
>>> already described in the DT:
>>>
>>>          uart: serial@10700 {
>>>              compatible = "ralink,rt2880-uart";
>>>              reg = <0x10700 0x30>;
>>>              interrupts = <1 IRQ_TYPE_LEVEL_HIGH>;
>>>              clock-frequency = <7372800>;
>>>              reg-shift = <2>;
>>>          };
>>>
>>> Are we supposed to duplicate such information (ie: addr) in the
>>> commandline as well?
>>>
>>
>> By the way, I tried using the following command line
>> 'console=uart,mmio32,0x10700,115200n8r mem=256M earlyprintk debug
>> ignore_loglevel' but I think I'm still missing something regarding this,
>> because it does not work, here's a log of Linux 4.1.13+:
>>
>>
>> 1: [arch/arm/kernel/setup.c:932] setup_arch(): r1 = 0xf34, r2 =
>> 0x803b3b50, cmdline ''
>> 1: [arch/arm/kernel/devtree.c:195] arch_get_next_mach(): infoBegin
>> 0xc024faac, mdesc 0xc024faac
>> 1: [arch/arm/kernel/devtree.c:195] arch_get_next_mach(): infoBegin
>> 0xc024faac, mdesc 0xc024fb14
>> 1: [drivers/of/fdt.c:106] of_fdt_is_compatible(): sigma,tango4 vs
>> sigma,vantage-1172
>> 1: [arch/arm/kernel/devtree.c:195] arch_get_next_mach(): infoBegin
>> 0xc024faac, mdesc 0xc024fb7c
>> 1: [drivers/of/fdt.c:749] of_flat_dt_match_machine(): Machine model:
>> Sigma Designs SMP8758 Vantage-1172 Rev E1
>> 1: [arch/arm/kernel/devtree.c:256] setup_machine_fdt(): about to call
>> early_init_dt_scan_nodes
>> 1: [drivers/of/fdt.c:1057] early_init_dt_scan_nodes(): bootcmdline ''
>> 1: [drivers/of/fdt.c:1062] early_init_dt_scan_nodes(): bootcmdline after
>> of_scan_flat_dt 'console=uart,mmio32,0x10700,115200n8r mem=256M
>> earlyprintk debug ignore_loglevel'
>> 1: [arch/arm/kernel/setup.c:946] setup_arch(): using DT at r2
>> 1: [arch/arm/kernel/setup.c:949] setup_arch(): machine name Sigma Tango DT
>> 1: [arch/arm/kernel/setup.c:967] setup_arch(): before parse_early_param
>> 1: [init/main.c:468] parse_early_param(): bootcmdline
>> 'console=uart,mmio32,0x10700,115200n8r mem=256M earlyprintk debug
>> ignore_loglevel'
>> 1: [init/main.c:473] parse_early_param(): mark
>> 1: [init/main.c:428] do_early_param(): enter with: 'console'
>> 'uart,mmio32,0x10700,115200n8r'
>> 1: [init/main.c:446] do_early_param(): 'earlycon', setup_func 0xc024b868
>> 1: [drivers/tty/serial/earlycon.c:214] param_setup_earlycon():
>> 'uart,mmio32,0x10700,115200n8r'
>> 1: [drivers/tty/serial/earlycon.c:181] setup_earlycon():
>> 'uart,mmio32,0x10700,115200n8r'
>> 1: [drivers/tty/serial/earlycon.c:132] register_earlycon():
>> 'mmio32,0x10700,115200n8r' 'uart'
>> 1: [drivers/tty/serial/earlycon.c:86] parse_options():
>> 'mmio32,0x10700,115200n8r'
>> 1: [drivers/tty/serial/earlycon.c:91] parse_options(): addr 0x00010700,
>> options '115200n8r'
>> 1: [drivers/tty/serial/earlycon.c:117] parse_options(): Early serial
>> console at MMIO32 0x10700 (options '115200n8r')
>> 1: [drivers/tty/serial/earlycon.c:138] register_earlycon(): '(null)'
>> 1: [drivers/tty/serial/earlycon.c:62] earlycon_map(): paddr 0x00010700
>> size 64
>>
>> As you can see, now that the options are more complete, the match for
>> "earlycon" succeeds, but it does not work, the last log is in
>> earlycon_map() function.
>> When using just "console=uart", the "earlycon" match will fail but a
>> match for "earlyprink" will succeed. That one will hook printch() from
>> the arch-dependent code to a somewhat simpler 'earlycon'
>> (arch/arm/kernel/early_printk.c).
>>
>> I think the code is the same on mainline.
>>
>> Also, regarding my previous question about using a HW described in DT
>> for earlycon, I noticed there's a of_setup_earlycon() in
>> drivers/tty/serial/earlycon.c but that is hooked to
>> drivers/of/fdt.c:setup_of_earlycon() which is not called. I do have
>> CONFIG_SERIAL_EARLYCON=y.
>>
>> I also have a similar issue (ie: get blocked right after the call to
>> earlycon_map function, log is obviously different from above) if attempt
>> to use of_setup_earlycon.
>> My DT has roughly:
>>
>>      aliases {
>>          serial0 = &uart;
>>      };
>>
>>      chosen {
>>             bootargs = "earlycon console mem=256M earlyprintk debug
>> ignore_loglevel";
>>             stdout-path = "serial0:115200n8";
>>      };
>>
>>      uart: serial@10700 {
>>          compatible = "ralink,rt2880-uart";
>>          reg = <0x10700 0x30>;
>>          interrupts = <1 IRQ_TYPE_LEVEL_HIGH>;
>>          clock-frequency = <7372800>;
>>          reg-shift = <2>;
>>      };
>>
>>
>> and then I hack drivers/tty/serial/8250/8250_early.c by adding:
>>
>>      OF_EARLYCON_DECLARE(rt2880, "ralink,rt2880-uart",
>> early_serial8250_setup);

There is no support for this uart in 8250 earlycon; the registers
need remapped.

>> at the end of the file, trying to mimic commit
>> d05f15707bb7659d2b863fafa1a918f286d74a63
>>
>> I'm still trying to figure out the right bootargs, so that's why both
>> "earlycon" and "console" are there. Suggestions welcome.

Just 'earlycon' triggers the attempted registration of earlycon matching the
compatible string of the stdout-path node.

The empty 'console' in bootargs is doing nothing.


> Does anybody has comments or suggestions regarding this thread and the issue above?

Regards,
Peter Hurley

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#1306573

Hi Peter,

On 01/11/2016 05:11 PM, Peter Hurley wrote:
> On 01/11/2016 07:07 AM, Sebastian Frias wrote:
>> On 12/22/2015 06:56 PM, Sebastian Frias wrote:
>>>
>>>       OF_EARLYCON_DECLARE(rt2880, "ralink,rt2880-uart",
>>> early_serial8250_setup);
>
> There is no support for this uart in 8250 earlycon; the registers
> need remapped.

Ok, two questions then:
1) If the UART is not supported on 8250 earlycon, what is the 
suggested/advised solution? Using just "earlyprintk"?
2) What would it take to make the "rt2880" work with the 8250 earlycon? 
I mean, it is already pretty much supported in there, what would be 
missing? (I don't see why it blocks on earlycon_map) And would it be 
worth doing?

>
>>> at the end of the file, trying to mimic commit
>>> d05f15707bb7659d2b863fafa1a918f286d74a63
>>>
>>> I'm still trying to figure out the right bootargs, so that's why both
>>> "earlycon" and "console" are there. Suggestions welcome.
>
> Just 'earlycon' triggers the attempted registration of earlycon matching the
> compatible string of the stdout-path node.
>
> The empty 'console' in bootargs is doing nothing.

Ok, thanks.

So, just to recap.
We would like to understand what is the right way of doing this:

- we are using 8250 (rt288x variant) UART: CONFIG_SERIAL_8250_RT288X=y
- the UART hardware is setup prior to Linux boot
- we don't want Linux to change the UART settings, just to pick up 
whatever settings the UART has and take over the UART.

There were two replies to that, one by Greg Kroah-Hartman 
(http://www.spinics.net/lists/linux-serial/msg20278.html) and one by 
you, where you suggested we use "console=uart", but as I reported 
(http://www.spinics.net/lists/linux-serial/msg20307.html) it does not 
work, you replied that iotype and mmio are not optional but mandatory 
(http://www.spinics.net/lists/linux-serial/msg20310.html), and I 
wondered if it was really necessary to duplicate data that is already on 
the DT among other questions 
(http://www.spinics.net/lists/linux-serial/msg20383.html), like how are 
DT described drivers supposed to interact with the 
"console="/"earlycon=" commandlines, or, the contradiction between 
"console=ttyS0" means '9600n81' and "if unspecified [the uart options], 
the h/w is not re-initialized"

So, for us, it is still not clear what is the recommended way of 
achieving our goal above, and it seems it is not clear what does 
"console=ttyS0" is supposed to do, hardcode ('9600n81') or probe ('the 
h/w is not re-initialized')
Any help will be appreciated.

Thanks, best regards,

Sebastian

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#1306606

On 01/11/2016 09:56 AM, Sebastian Frias wrote:
> Hi Peter,
> 
> On 01/11/2016 05:11 PM, Peter Hurley wrote:
>> On 01/11/2016 07:07 AM, Sebastian Frias wrote:
>>> On 12/22/2015 06:56 PM, Sebastian Frias wrote:
>>>>
>>>>       OF_EARLYCON_DECLARE(rt2880, "ralink,rt2880-uart",
>>>> early_serial8250_setup);
>>
>> There is no support for this uart in 8250 earlycon; the registers
>> need remapped.
> 
> Ok, two questions then:
> 1) If the UART is not supported on 8250 earlycon, what is the
> suggested/advised solution? Using just "earlyprintk"?

I don't have enough information to suggest what you "should" use
here.

Is this going to be a shipping product?
Is it single-core?
etc.

And what is your purpose for outputting early boot information
before loading the serial driver which does provide console output?


> 2) What would it take to make the "rt2880" work with the 8250
> earlycon? I mean, it is already pretty much supported in there, what
> would be missing? (I don't see why it blocks on earlycon_map) And
> would it be worth doing?

The rt2880 does not have the same register locations as a 8250.
The 8250 port driver remaps all register accesses with a LUT.

Adding support would be trivial.

>>>> at the end of the file, trying to mimic commit
>>>> d05f15707bb7659d2b863fafa1a918f286d74a63
>>>>
>>>> I'm still trying to figure out the right bootargs, so that's why both
>>>> "earlycon" and "console" are there. Suggestions welcome.
>>
>> Just 'earlycon' triggers the attempted registration of earlycon matching the
>> compatible string of the stdout-path node.
>>
>> The empty 'console' in bootargs is doing nothing.
> 
> Ok, thanks.
> 
> So, just to recap.
> We would like to understand what is the right way of doing this:
> 
> - we are using 8250 (rt288x variant) UART: CONFIG_SERIAL_8250_RT288X=y
> - the UART hardware is setup prior to Linux boot
> - we don't want Linux to change the UART settings, just to pick up
> whatever settings the UART has and take over the UART. 
> There were two replies to that, one by Greg Kroah-Hartman
> (http://www.spinics.net/lists/linux-serial/msg20278.html) and one by
> you, where you suggested we use "console=uart", but as I reported
> (http://www.spinics.net/lists/linux-serial/msg20307.html) it does not
> work, you replied that iotype and mmio are not optional but mandatory
> (http://www.spinics.net/lists/linux-serial/msg20310.html), and I
> wondered if it was really necessary to duplicate data that is already
> on the DT among other questions

At the time, I didn't know you were describing your h/w with DT.

If you use the console command line (console= or earlycon=) to start
an earlycon, then the uart address and iotype are mandatory.
For this usage, earlycon matching is attempted with every EARLYCON_DECLARE().

If you use plain "earlycon" on the command line, that will attempt to
register the uart described by stdout-path in DT. For this usage,
earlycon matching is attempted with the compatible string of every
OF_EARLYCON_DECLARE().

> (http://www.spinics.net/lists/linux-serial/msg20383.html), like how
> are DT described drivers supposed to interact with the
> "console="/"earlycon=" commandlines

They don't; those are orthogonal.

>, or, the contradiction between
> "console=ttyS0" means '9600n81' and "if unspecified [the uart
> options], the h/w is not re-initialized"> 

I thought I was clear on that: "console=ttyS0" initializes the h/w
to 9600n81 *because there are already existing users that must not break*.

"console=uart,..." probes the h/w
*because there are already existing users that must not break *

> So, for us, it is still not clear what is the recommended way of
> achieving our goal above, and it seems it is not clear what does
> "console=ttyS0" is supposed to do, hardcode ('9600n81') or probe
> ('the h/w is not re-initialized')

The DT way will be simplest at this point because you won't
have to write console handover matching for "console=rt288x,..."

With DT (ie, stdout-path) earlycon, when a serial driver loads,
an attempt is made to cross-reference any existing console with
the node that is loading and will do a console takeover from
a running earlycon for a matching uart node.

There is a bug with DT earlycon though.
If you have a dummy console that loads, the DT earlycon is
disabled at that point because boot consoles are disabled when
"real" consoles load.

> Any help will be appreciated.

Regards,
Peter Hurley

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#1306635

On 01/11/2016 11:06 AM, Peter Hurley wrote:
> On 01/11/2016 09:56 AM, Sebastian Frias wrote:
>> On 01/11/2016 05:11 PM, Peter Hurley wrote:
>>> On 01/11/2016 07:07 AM, Sebastian Frias wrote:
>>>> On 12/22/2015 06:56 PM, Sebastian Frias wrote:

[...]

>> 2) What would it take to make the "rt2880" work with the 8250
>> earlycon? I mean, it is already pretty much supported in there, what
>> would be missing? (I don't see why it blocks on earlycon_map) And
>> would it be worth doing?
> 
> The rt2880 does not have the same register locations as a 8250.
> The 8250 port driver remaps all register accesses with a LUT.
> 
> Adding support would be trivial.

Please test.

--- >% ---
Subject: [PATCH] serial: 8250: Add Au1x00/RT288x earlycon support

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
 drivers/tty/serial/8250/8250_early.c | 52 ++++++++++++++++++++++++++++++++++++
 include/uapi/linux/serial_reg.h      | 13 +++++++++
 2 files changed, 65 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
index af62131..307fb23 100644
--- a/drivers/tty/serial/8250/8250_early.c
+++ b/drivers/tty/serial/8250/8250_early.c
@@ -145,3 +145,55 @@ EARLYCON_DECLARE(uart8250, early_serial8250_setup);
 EARLYCON_DECLARE(uart, early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
+
+
+#ifdef CONFIG_SERIAL_8250_RT288X
+
+static void __init rt288x_putc(struct uart_port *port, int c)
+{
+	unsigned int status;
+
+	serial8250_early_out(port, AU1x00_TX, c);
+
+	for (;;) {
+		status = serial8250_early_in(port, AU1x00_LSR);
+		if ((status & BOTH_EMPTY) == BOTH_EMPTY)
+			break;
+		cpu_relax();
+	}
+}
+
+static void __init early_rt288x_write(struct console *console,
+				      const char *s, unsigned int count)
+{
+	struct earlycon_device *device = console->data;
+	struct uart_port *port = &device->port;
+
+	uart_console_write(port, s, count, rt288x_putc);
+}
+
+static int __init early_rt288x_setup(struct earlycon_device *device,
+				     const char *options)
+{
+	struct uart_port *port = &device->port;
+	unsigned int ier;
+
+	if (!(device->port.membase || device->port.iobase))
+		return -ENODEV;
+
+	/* Don't support direct init or any line-setting options */
+	if (device->baud)
+		return -EINVAL;
+
+	/* assume the device was initialized, only mask interrupts */
+	ier = serial8250_early_in(port, AU1x00_IER);
+	serial8250_early_out(port, AU1x00_IER, ier);
+
+	device->con->write = early_rt288x_write;
+	return 0;
+}
+
+EARLYCON_DECLARE(rt288x, early_rt288x_setup);
+OF_EARLYCON_DECLARE(rt288x, "ralink,rt2880-uart", early_rt288x_setup);
+
+#endif /* CONFIG_SERIAL_8250_RT288X */
diff --git a/include/uapi/linux/serial_reg.h b/include/uapi/linux/serial_reg.h
index 1e5ac4e7..4d068ac 100644
--- a/include/uapi/linux/serial_reg.h
+++ b/include/uapi/linux/serial_reg.h
@@ -376,5 +376,18 @@
 #define UART_EXAR_TXTRG		0x0a	/* Tx FIFO trigger level write-only */
 #define UART_EXAR_RXTRG		0x0b	/* Rx FIFO trigger level write-only */
 
+/*
+ * Register offsets for Au1x00/RT288x 8250-workalikes
+ */
+#define AU1x00_RX	0
+#define AU1x00_TX	1
+#define AU1x00_IER	2
+#define AU1x00_IIR	3
+#define AU1x00_FCR	4
+#define AU1x00_LCR	5
+#define AU1x00_MCR	6
+#define AU1x00_LSR	7
+#define AU1x00_MSR	8
+
 #endif /* _LINUX_SERIAL_REG_H */
 
-- 
2.7.0

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#1306657

On 01/11/2016 11:57 AM, Peter Hurley wrote:
> On 01/11/2016 11:06 AM, Peter Hurley wrote:
>> On 01/11/2016 09:56 AM, Sebastian Frias wrote:
>>> On 01/11/2016 05:11 PM, Peter Hurley wrote:
>>>> On 01/11/2016 07:07 AM, Sebastian Frias wrote:
>>>>> On 12/22/2015 06:56 PM, Sebastian Frias wrote:
> 
> [...]
> 
>>> 2) What would it take to make the "rt2880" work with the 8250
>>> earlycon? I mean, it is already pretty much supported in there, what
>>> would be missing? (I don't see why it blocks on earlycon_map) And
>>> would it be worth doing?
>>
>> The rt2880 does not have the same register locations as a 8250.
>> The 8250 port driver remaps all register accesses with a LUT.
>>
>> Adding support would be trivial.
> 
> Please test.

To get this working with DT, you may need to apply part or all of
my "Earlycon cleanup" series from Apr last year that adds the 
necessary support for things like "reg-shift" DT properties.

I'll see what I can do about cleaning up and re-submitting that series.

Regards,
Peter Hurley


> --- >% ---
> Subject: [PATCH] serial: 8250: Add Au1x00/RT288x earlycon support
> 
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
> ---
>  drivers/tty/serial/8250/8250_early.c | 52 ++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/serial_reg.h      | 13 +++++++++
>  2 files changed, 65 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
> index af62131..307fb23 100644
> --- a/drivers/tty/serial/8250/8250_early.c
> +++ b/drivers/tty/serial/8250/8250_early.c
> @@ -145,3 +145,55 @@ EARLYCON_DECLARE(uart8250, early_serial8250_setup);
>  EARLYCON_DECLARE(uart, early_serial8250_setup);
>  OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
>  OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
> +
> +
> +#ifdef CONFIG_SERIAL_8250_RT288X
> +
> +static void __init rt288x_putc(struct uart_port *port, int c)
> +{
> +	unsigned int status;
> +
> +	serial8250_early_out(port, AU1x00_TX, c);
> +
> +	for (;;) {
> +		status = serial8250_early_in(port, AU1x00_LSR);
> +		if ((status & BOTH_EMPTY) == BOTH_EMPTY)
> +			break;
> +		cpu_relax();
> +	}
> +}
> +
> +static void __init early_rt288x_write(struct console *console,
> +				      const char *s, unsigned int count)
> +{
> +	struct earlycon_device *device = console->data;
> +	struct uart_port *port = &device->port;
> +
> +	uart_console_write(port, s, count, rt288x_putc);
> +}
> +
> +static int __init early_rt288x_setup(struct earlycon_device *device,
> +				     const char *options)
> +{
> +	struct uart_port *port = &device->port;
> +	unsigned int ier;
> +
> +	if (!(device->port.membase || device->port.iobase))
> +		return -ENODEV;
> +
> +	/* Don't support direct init or any line-setting options */
> +	if (device->baud)
> +		return -EINVAL;
> +
> +	/* assume the device was initialized, only mask interrupts */
> +	ier = serial8250_early_in(port, AU1x00_IER);
> +	serial8250_early_out(port, AU1x00_IER, ier);
> +
> +	device->con->write = early_rt288x_write;
> +	return 0;
> +}
> +
> +EARLYCON_DECLARE(rt288x, early_rt288x_setup);
> +OF_EARLYCON_DECLARE(rt288x, "ralink,rt2880-uart", early_rt288x_setup);
> +
> +#endif /* CONFIG_SERIAL_8250_RT288X */
> diff --git a/include/uapi/linux/serial_reg.h b/include/uapi/linux/serial_reg.h
> index 1e5ac4e7..4d068ac 100644
> --- a/include/uapi/linux/serial_reg.h
> +++ b/include/uapi/linux/serial_reg.h
> @@ -376,5 +376,18 @@
>  #define UART_EXAR_TXTRG		0x0a	/* Tx FIFO trigger level write-only */
>  #define UART_EXAR_RXTRG		0x0b	/* Rx FIFO trigger level write-only */
>  
> +/*
> + * Register offsets for Au1x00/RT288x 8250-workalikes
> + */
> +#define AU1x00_RX	0
> +#define AU1x00_TX	1
> +#define AU1x00_IER	2
> +#define AU1x00_IIR	3
> +#define AU1x00_FCR	4
> +#define AU1x00_LCR	5
> +#define AU1x00_MCR	6
> +#define AU1x00_LSR	7
> +#define AU1x00_MSR	8
> +
>  #endif /* _LINUX_SERIAL_REG_H */
>  
> 

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#1307158

On 11/01/2016 20:06, Peter Hurley wrote:

> I don't have enough information to suggest what you "should" use
> here.
> 
> Is this going to be a shipping product?
> Is it single-core?
> etc.
> 
> And what is your purpose for outputting early boot information
> before loading the serial driver which does provide console output?

I'm not sure exactly which board Sebastian has in mind, but I've been
using the SERIAL_8250_RT288X driver on my Tango4 board.

Note: calling the UART driver "Au1x00/RT288x" is a bit of a misnomer,
as these are names of SoCs using that distinct register layout.
The actual IP is probably the 16550-compatible Palmchip BK-3103.
https://sites.google.com/a/palmchiptech.com/palmchiptech/product-services/hardware-services/ip-cores/bk-3103
(Not sure that this website is legitimate, though.)

When I need earlyprintk support, I use this patch from Mans:
http://thread.gmane.org/gmane.linux.kernel/2081016

Regards.

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#1307471

On 01/12/2016 10:37 AM, Mason wrote:
> On 11/01/2016 20:06, Peter Hurley wrote:
>
>> I don't have enough information to suggest what you "should" use
>> here.
>>
>> Is this going to be a shipping product?
>> Is it single-core?
>> etc.
>>
>> And what is your purpose for outputting early boot information
>> before loading the serial driver which does provide console output?
>
> I'm not sure exactly which board Sebastian has in mind, but I've been
> using the SERIAL_8250_RT288X driver on my Tango4 board.

For the record, I'm using a SoC emulator, and thus do not have a 
bootloader per se and there are a bunch of other things that I cannot 
count on.
The emulator has the UART pre-setup, so I just need Linux to take over 
without changing the parameters.
Ideally, I would like to have the same image of Linux+DT to start in any 
instance of the emulator or real chips, regardless of the clock ratios, 
that's why I sort of need Linux to not change the UART speed, which is 
quite tricky because there are no clock generators in the emulator.

NOTE: on my tree I'm using the patch I previously submitted here, so 
Linux is probing the UART so it works for all my cases, but I would like 
to go back to a standard tree.

>
> Note: calling the UART driver "Au1x00/RT288x" is a bit of a misnomer,
> as these are names of SoCs using that distinct register layout.
> The actual IP is probably the 16550-compatible Palmchip BK-3103.
> https://sites.google.com/a/palmchiptech.com/palmchiptech/product-services/hardware-services/ip-cores/bk-3103
> (Not sure that this website is legitimate, though.)
>
> When I need earlyprintk support, I use this patch from Mans:
> http://thread.gmane.org/gmane.linux.kernel/2081016
>
> Regards.
>

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#1307774

On 01/12/2016 06:22 AM, Sebastian Frias wrote:
> On 01/12/2016 10:37 AM, Mason wrote:
>> On 11/01/2016 20:06, Peter Hurley wrote:
>>
>>> I don't have enough information to suggest what you "should" use
>>> here.
>>>
>>> Is this going to be a shipping product?
>>> Is it single-core?
>>> etc.
>>>
>>> And what is your purpose for outputting early boot information
>>> before loading the serial driver which does provide console output?
>>
>> I'm not sure exactly which board Sebastian has in mind, but I've been
>> using the SERIAL_8250_RT288X driver on my Tango4 board.
> 
> For the record, I'm using a SoC emulator, and thus do not have a bootloader per se and there are a bunch of other things that I cannot count on.
> The emulator has the UART pre-setup, so I just need Linux to take over without changing the parameters.
> Ideally, I would like to have the same image of Linux+DT to start in any instance of the emulator or real chips, regardless of the clock ratios, that's why I sort of need Linux to not change the UART speed, which is quite tricky because there are no clock generators in the emulator.

Got it, thanks for the info.
Please test the series I just cc'd you on plus the patch I sent
you yesterday.

That should get you an earlycon up and running on that simulator;
let me know if it doesn't and we'll go from there.

> NOTE: on my tree I'm using the patch I previously submitted here, so Linux is probing the UART so it works for all my cases, but I would like to go back to a standard tree.

I expect that patch to go into -next sometime during the 4.5-rc cycle.


Regards,
Peter Hurley

>> Note: calling the UART driver "Au1x00/RT288x" is a bit of a misnomer,
>> as these are names of SoCs using that distinct register layout.
>> The actual IP is probably the 16550-compatible Palmchip BK-3103.
>> https://sites.google.com/a/palmchiptech.com/palmchiptech/product-services/hardware-services/ip-cores/bk-3103
>> (Not sure that this website is legitimate, though.)
>>
>> When I need earlyprintk support, I use this patch from Mans:
>> http://thread.gmane.org/gmane.linux.kernel/2081016
>>
>> Regards.
>>

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#1307891

On 12/01/2016 20:47, Peter Hurley wrote:

> I expect that patch to go into -next sometime during the 4.5-rc cycle.

Do you mean the "Add Au1x00/RT288x earlycon support" patch?

I find it strange that you have rt288x_putc while also
using AU1x00_FOO. Seems like mixing naming styles.

Did you see my post about the underlying IP block?
Might be appropriate to use that name there?

Regards.

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#1307898

On 01/12/2016 02:26 PM, Mason wrote:
> On 12/01/2016 20:47, Peter Hurley wrote:
> 
>> I expect that patch to go into -next sometime during the 4.5-rc cycle.
> 
> Do you mean the "Add Au1x00/RT288x earlycon support" patch?

No. This one http://www.spinics.net/lists/linux-serial/msg20328.html

> I find it strange that you have rt288x_putc while also
> using AU1x00_FOO. Seems like mixing naming styles.

I wrote it in 10 mins.

> Did you see my post about the underlying IP block?
> Might be appropriate to use that name there?

I did, and thanks for reminding me. I did follow that email thread
a while back about the provenance of this register layout.

I'd rather not go back through the source and rename the symbols.
Afaict, the Au1x00 landed first in source and then the RT288x afterwards.
So I'd like to stick with those.

I named the register layout on the basis of the original usage
which started in the 8250 port driver with the au_* accessor functions.

The earlycon functions I named that way because that's the name of
the earlycon (which originates from the DT compatible key which can't be
changed).

I do want people to be able to find other relevant code by grepping
these names, so I was thinking of adding a follow-on patch that uses the
AU1x00_ register names in the 8250 port driver LUT.

Regards,
Peter Hurley

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#1308298

Hi Peter,

On 01/12/2016 08:47 PM, Peter Hurley wrote:
> On 01/12/2016 06:22 AM, Sebastian Frias wrote:
>>
>> For the record, I'm using a SoC emulator, and thus do not have a bootloader per se and there are a bunch of other things that I cannot count on.
>> The emulator has the UART pre-setup, so I just need Linux to take over without changing the parameters.
>> Ideally, I would like to have the same image of Linux+DT to start in any instance of the emulator or real chips, regardless of the clock ratios, that's why I sort of need Linux to not change the UART speed, which is quite tricky because there are no clock generators in the emulator.
>
> Got it, thanks for the info.
> Please test the series I just cc'd you on plus the patch I sent
> you yesterday.
>
> That should get you an earlycon up and running on that simulator;
> let me know if it doesn't and we'll go from there.

Ok, thanks.
I will try as soon as we finish rebasing our changes on top of 
"mainline" (or HEAD, or is it "-next"? I don't know how you guys call 
the most recent code base for Linux)

Actually, I tried yesterday on a 4.1.13 but 
"[drivers/tty/serial/earlycon.c:62] earlycon_map()" was still the last 
message I got, just as with the OF_EARLYCON_DECLARE hack I had 
previously talk about, and so I would like to test on the same 
conditions than you, mainline.

>
>> NOTE: on my tree I'm using the patch I previously submitted here, so Linux is probing the UART so it works for all my cases, but I would like to go back to a standard tree.
>
> I expect that patch to go into -next sometime during the 4.5-rc cycle.

Sounds good!
Thanks,

Sebastian

>
>
> Regards,
> Peter Hurley
>
>>> Note: calling the UART driver "Au1x00/RT288x" is a bit of a misnomer,
>>> as these are names of SoCs using that distinct register layout.
>>> The actual IP is probably the 16550-compatible Palmchip BK-3103.
>>> https://sites.google.com/a/palmchiptech.com/palmchiptech/product-services/hardware-services/ip-cores/bk-3103
>>> (Not sure that this website is legitimate, though.)
>>>
>>> When I need earlyprintk support, I use this patch from Mans:
>>> http://thread.gmane.org/gmane.linux.kernel/2081016
>>>
>>> Regards.
>>>
>

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#1308578

On 01/13/2016 03:14 AM, Sebastian Frias wrote:
> Hi Peter,
> 
> On 01/12/2016 08:47 PM, Peter Hurley wrote:
>> On 01/12/2016 06:22 AM, Sebastian Frias wrote:
>>>
>>> For the record, I'm using a SoC emulator, and thus do not have a bootloader per se and there are a bunch of other things that I cannot count on.
>>> The emulator has the UART pre-setup, so I just need Linux to take over without changing the parameters.
>>> Ideally, I would like to have the same image of Linux+DT to start in any instance of the emulator or real chips, regardless of the clock ratios, that's why I sort of need Linux to not change the UART speed, which is quite tricky because there are no clock generators in the emulator.
>>
>> Got it, thanks for the info.
>> Please test the series I just cc'd you on plus the patch I sent
>> you yesterday.
>>
>> That should get you an earlycon up and running on that simulator;
>> let me know if it doesn't and we'll go from there.
> 
> Ok, thanks.
> I will try as soon as we finish rebasing our changes on top of
> "mainline" (or HEAD, or is it "-next"? I don't know how you guys call
> the most recent code base for Linux)

The basic tree organization is

   Linus's tree  <---- linux-next[date]  <----- maintainers' trees
   (mainline)          (next)                   (eg., Greg's tty tree)

The patches I sent you (along with any required modifications during the
review cycle) are based on the tty-next branch in Greg's tty tree here
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git

As of this email, Greg's tree is based on Linus's 4.4-rc6 which should
be stable enough for you to test these patches on.

> Actually, I tried yesterday on a 4.1.13 but
> "[drivers/tty/serial/earlycon.c:62] earlycon_map()" was still the
> last message I got, just as with the OF_EARLYCON_DECLARE hack I had
> previously talk about, and so I would like to test on the same
> conditions than you, mainline.

So just to confirm, you applied "8250: Add Au1x00/RT288x earlycon support"
to 4.1.13 and the earlycon didn't come up when you used the kernel
command line option like so:

	earlycon=rt288x,mmio32,0x10700

Is that correct?

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#1307463

Hi Peter,

On 01/11/2016 08:06 PM, Peter Hurley wrote:
> On 01/11/2016 09:56 AM, Sebastian Frias wrote:
>> Hi Peter,
>>
>> On 01/11/2016 05:11 PM, Peter Hurley wrote:
>>> On 01/11/2016 07:07 AM, Sebastian Frias wrote:
>>>> On 12/22/2015 06:56 PM, Sebastian Frias wrote:
>>>>>
>>>>>        OF_EARLYCON_DECLARE(rt2880, "ralink,rt2880-uart",
>>>>> early_serial8250_setup);
>>>
>>> There is no support for this uart in 8250 earlycon; the registers
>>> need remapped.
>>
>> Ok, two questions then:
>> 1) If the UART is not supported on 8250 earlycon, what is the
>> suggested/advised solution? Using just "earlyprintk"?
>
> I don't have enough information to suggest what you "should" use
> here.
>
> Is this going to be a shipping product?
> Is it single-core?
> etc.
>
> And what is your purpose for outputting early boot information
> before loading the serial driver which does provide console output?
>

No, it is not for production, just for debug, but we would like to 
understand if there is a standard way of doing so, so that whenever 
somebody ask us for "early print", we can provide with the good way.
I know we can always provide with hacks, I'm just wondering if there's a 
"standard way".

>
>> 2) What would it take to make the "rt2880" work with the 8250
>> earlycon? I mean, it is already pretty much supported in there, what
>> would be missing? (I don't see why it blocks on earlycon_map) And
>> would it be worth doing?
>
> The rt2880 does not have the same register locations as a 8250.
> The 8250 port driver remaps all register accesses with a LUT.
>
> Adding support would be trivial.

Ok, I will see if I can find some commit that does something similar to 
get some inspiration.

>
>>>>> at the end of the file, trying to mimic commit
>>>>> d05f15707bb7659d2b863fafa1a918f286d74a63
>>>>>
>>>>> I'm still trying to figure out the right bootargs, so that's why both
>>>>> "earlycon" and "console" are there. Suggestions welcome.
>>>
>>> Just 'earlycon' triggers the attempted registration of earlycon matching the
>>> compatible string of the stdout-path node.
>>>
>>> The empty 'console' in bootargs is doing nothing.
>>
>> Ok, thanks.
>>
>> So, just to recap.
>> We would like to understand what is the right way of doing this:
>>
>> - we are using 8250 (rt288x variant) UART: CONFIG_SERIAL_8250_RT288X=y
>> - the UART hardware is setup prior to Linux boot
>> - we don't want Linux to change the UART settings, just to pick up
>> whatever settings the UART has and take over the UART.
>> There were two replies to that, one by Greg Kroah-Hartman
>> (http://www.spinics.net/lists/linux-serial/msg20278.html) and one by
>> you, where you suggested we use "console=uart", but as I reported
>> (http://www.spinics.net/lists/linux-serial/msg20307.html) it does not
>> work, you replied that iotype and mmio are not optional but mandatory
>> (http://www.spinics.net/lists/linux-serial/msg20310.html), and I
>> wondered if it was really necessary to duplicate data that is already
>> on the DT among other questions
>
> At the time, I didn't know you were describing your h/w with DT.

Oh, sorry for the inconvenience then.

>
> If you use the console command line (console= or earlycon=) to start
> an earlycon, then the uart address and iotype are mandatory.
> For this usage, earlycon matching is attempted with every EARLYCON_DECLARE().
>
> If you use plain "earlycon" on the command line, that will attempt to
> register the uart described by stdout-path in DT. For this usage,
> earlycon matching is attempted with the compatible string of every
> OF_EARLYCON_DECLARE().

I see, and since rt288x variant is not fully supported (no 
OF_EARLYCON_DECLARE) "earlycon" fails.

>
>> (http://www.spinics.net/lists/linux-serial/msg20383.html), like how
>> are DT described drivers supposed to interact with the
>> "console="/"earlycon=" commandlines
>
> They don't; those are orthogonal.

Ok.

>
>> , or, the contradiction between
>> "console=ttyS0" means '9600n81' and "if unspecified [the uart
>> options], the h/w is not re-initialized">
>
> I thought I was clear on that: "console=ttyS0" initializes the h/w
> to 9600n81 *because there are already existing users that must not break*.
>
> "console=uart,..." probes the h/w
> *because there are already existing users that must not break *

Thanks, I had misunderstood.

>
>> So, for us, it is still not clear what is the recommended way of
>> achieving our goal above, and it seems it is not clear what does
>> "console=ttyS0" is supposed to do, hardcode ('9600n81') or probe
>> ('the h/w is not re-initialized')
>
> The DT way will be simplest at this point because you won't
> have to write console handover matching for "console=rt288x,..."
>
> With DT (ie, stdout-path) earlycon, when a serial driver loads,
> an attempt is made to cross-reference any existing console with
> the node that is loading and will do a console takeover from
> a running earlycon for a matching uart node.
>
> There is a bug with DT earlycon though.
> If you have a dummy console that loads, the DT earlycon is
> disabled at that point because boot consoles are disabled when
> "real" consoles load.

I'm sorry for my ignorance, but what is a "dummy console"? Under what 
circumstances would it load and this bug be seen?

Regards,

Sebastian

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#1307842

Hi Sebastian,

On 01/12/2016 06:14 AM, Sebastian Frias wrote:
> On 01/11/2016 08:06 PM, Peter Hurley wrote:
>> On 01/11/2016 09:56 AM, Sebastian Frias wrote:
>>> On 01/11/2016 05:11 PM, Peter Hurley wrote:
>>>> On 01/11/2016 07:07 AM, Sebastian Frias wrote:
>>>>> On 12/22/2015 06:56 PM, Sebastian Frias wrote:
>>>>>>
>>>>>>        OF_EARLYCON_DECLARE(rt2880, "ralink,rt2880-uart",
>>>>>> early_serial8250_setup);
>>>>
>>>> There is no support for this uart in 8250 earlycon; the registers
>>>> need remapped.
>>>
>>> Ok, two questions then:
>>> 1) If the UART is not supported on 8250 earlycon, what is the
>>> suggested/advised solution? Using just "earlyprintk"?
>>
>> I don't have enough information to suggest what you "should" use
>> here.
>>
>> Is this going to be a shipping product?
>> Is it single-core?
>> etc.
>>
>> And what is your purpose for outputting early boot information
>> before loading the serial driver which does provide console output?
>>
> 
> No, it is not for production, just for debug, but we would like to understand if there is a standard way of doing so, so that whenever somebody ask us for "early print", we can provide with the good way.
> I know we can always provide with hacks, I'm just wondering if there's a "standard way".

Ok.

The "standard" solution is either command-line or DT earlycon (which
we've established isn't working for your setup).

Let's fix that so that both of those options work.


>>> 2) What would it take to make the "rt2880" work with the 8250
>>> earlycon? I mean, it is already pretty much supported in there, what
>>> would be missing? (I don't see why it blocks on earlycon_map) And
>>> would it be worth doing?
>>
>> The rt2880 does not have the same register locations as a 8250.
>> The 8250 port driver remaps all register accesses with a LUT.
>>
>> Adding support would be trivial.
> 
> Ok, I will see if I can find some commit that does something similar to get some inspiration.

I sent you a patch yesterday that adds earlycon support for
this uart (so command line should work), plus the series I sent today
should get DT earlycon up and running. Please test both.


>>>>>> at the end of the file, trying to mimic commit
>>>>>> d05f15707bb7659d2b863fafa1a918f286d74a63
>>>>>>
>>>>>> I'm still trying to figure out the right bootargs, so that's why both
>>>>>> "earlycon" and "console" are there. Suggestions welcome.
>>>>
>>>> Just 'earlycon' triggers the attempted registration of earlycon matching the
>>>> compatible string of the stdout-path node.
>>>>
>>>> The empty 'console' in bootargs is doing nothing.
>>>
>>> Ok, thanks.
>>>
>>> So, just to recap.
>>> We would like to understand what is the right way of doing this:
>>>
>>> - we are using 8250 (rt288x variant) UART: CONFIG_SERIAL_8250_RT288X=y
>>> - the UART hardware is setup prior to Linux boot
>>> - we don't want Linux to change the UART settings, just to pick up
>>> whatever settings the UART has and take over the UART.
>>> There were two replies to that, one by Greg Kroah-Hartman
>>> (http://www.spinics.net/lists/linux-serial/msg20278.html) and one by
>>> you, where you suggested we use "console=uart", but as I reported
>>> (http://www.spinics.net/lists/linux-serial/msg20307.html) it does not
>>> work, you replied that iotype and mmio are not optional but mandatory
>>> (http://www.spinics.net/lists/linux-serial/msg20310.html), and I
>>> wondered if it was really necessary to duplicate data that is already
>>> on the DT among other questions
>>
>> At the time, I didn't know you were describing your h/w with DT.
> 
> Oh, sorry for the inconvenience then.

No big deal, I was just explaining the earlier advice.


>> If you use the console command line (console= or earlycon=) to start
>> an earlycon, then the uart address and iotype are mandatory.
>> For this usage, earlycon matching is attempted with every EARLYCON_DECLARE().
>>
>> If you use plain "earlycon" on the command line, that will attempt to
>> register the uart described by stdout-path in DT. For this usage,
>> earlycon matching is attempted with the compatible string of every
>> OF_EARLYCON_DECLARE().
> 
> I see, and since rt288x variant is not fully supported (no OF_EARLYCON_DECLARE) "earlycon" fails.

Yes.

>>> (http://www.spinics.net/lists/linux-serial/msg20383.html), like how
>>> are DT described drivers supposed to interact with the
>>> "console="/"earlycon=" commandlines
>>
>> They don't; those are orthogonal.
> 
> Ok.
> 
>>
>>> , or, the contradiction between
>>> "console=ttyS0" means '9600n81' and "if unspecified [the uart
>>> options], the h/w is not re-initialized">
>>
>> I thought I was clear on that: "console=ttyS0" initializes the h/w
>> to 9600n81 *because there are already existing users that must not break*.
>>
>> "console=uart,..." probes the h/w
>> *because there are already existing users that must not break *
> 
> Thanks, I had misunderstood.
> 
>>
>>> So, for us, it is still not clear what is the recommended way of
>>> achieving our goal above, and it seems it is not clear what does
>>> "console=ttyS0" is supposed to do, hardcode ('9600n81') or probe
>>> ('the h/w is not re-initialized')
>>
>> The DT way will be simplest at this point because you won't
>> have to write console handover matching for "console=rt288x,..."
>>
>> With DT (ie, stdout-path) earlycon, when a serial driver loads,
>> an attempt is made to cross-reference any existing console with
>> the node that is loading and will do a console takeover from
>> a running earlycon for a matching uart node.
>>
>> There is a bug with DT earlycon though.
>> If you have a dummy console that loads, the DT earlycon is
>> disabled at that point because boot consoles are disabled when
>> "real" consoles load.
> 
> I'm sorry for my ignorance, but what is a "dummy console"? Under what circumstances would it load and this bug be seen?

The dummy console is a hack used to preserve the priority of the
display console in the event no console is specified.

Here's an example:
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Initializing cgroup subsys cpuacct
[    0.000000] Linux version 4.4.0-rc6+ (peter@thor) (gcc version 4.8.2 (Ubuntu/Linaro 4.8.2-16ubuntu4) ) #86 PREEMPT Tue Jan 12 12:30:39 PST 2016
[    0.000000] CPU: ARMv7 Processor [413fc082] revision 2 (ARMv7), cr=10c5387d
[    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[    0.000000] Machine model: TI AM335x BeagleBone Black
[    0.000000] earlycon: omap8250 at MMIO 0x44e09000 (options '')
[    0.000000] bootconsole [omap8250] enabled
[    0.000000] cma: Reserved 16 MiB at 0x9f000000
[    0.000000] Memory policy: Data cache writeback
[    0.000000] CPU: All CPU(s) started in SVC mode.
[    0.000000] AM335X ES2.1 (sgx neon )
[    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 129920
[    0.000000] Kernel command line: earlycon root=/dev/mmcblk0p2 ro fixrtc rootfstype=ext4 rootwait
[    0.000000] PID hash table entries: 2048 (order: 1, 8192 bytes)
[    0.000000] Dentry cache hash table entries: 65536 (order: 6, 262144 bytes)
[    0.000000] Inode-cache hash table entries: 32768 (order: 5, 131072 bytes)
[    0.000000] Memory: 486332K/524288K available (10582K kernel code, 862K rwdata, 3396K rodata, 596K init, 871K bss, 21572K reserved, 16384K cma-reserved, 0K highmem)
[    0.000000] Virtual kernel memory layout:
[    0.000000]     vector  : 0xffff0000 - 0xffff1000   (   4 kB)
[    0.000000]     fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
[    0.000000]     vmalloc : 0xe0800000 - 0xff800000   ( 496 MB)
[    0.000000]     lowmem  : 0xc0000000 - 0xe0000000   ( 512 MB)
[    0.000000]     pkmap   : 0xbfe00000 - 0xc0000000   (   2 MB)
[    0.000000]     modules : 0xbf000000 - 0xbfe00000   (  14 MB)
[    0.000000]       .text : 0xc0008000 - 0xc0daebf0   (13979 kB)
[    0.000000]       .init : 0xc0daf000 - 0xc0e44000   ( 596 kB)
[    0.000000]       .data : 0xc0e44000 - 0xc0f1bb3c   ( 863 kB)
[    0.000000]        .bss : 0xc0f1e000 - 0xc0ff7d84   ( 872 kB)
[    0.000000] Preemptible hierarchical RCU implementation.
[    0.000000]  Build-time adjustment of leaf fanout to 32.
[    0.000000] NR_IRQS:16 nr_irqs:16 16
[    0.000000] IRQ: Found an INTC at 0xfa200000 (revision 5.0) with 128 interrupts
[    0.000000] OMAP clockevent source: timer2 at 24000000 Hz
[    0.000014] sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971ns
[    0.008083] clocksource: timer1: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 79635851949 ns
[    0.017570] OMAP clocksource: timer1 at 24000000 Hz
[    0.022969] Console: colour dummy device 80x30
[    0.027570] console [tty0] enabled
[    0.031100] bootconsole [omap8250] disabled
Ubuntu 14.04.3 LTS black ttyS0

black login:


As you can see, there's boot console but no regular console until
getty spawns.

I've fixed the problem once, but that broke some setups and had to be
reverted so I need to rethink an alternate approach. A unified, coherent
solution is elusive because of the many different possible console setups.

Regards,
Peter Hurley

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