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[PATCH] arm: rpi: Device tree modifications for U-Boot

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  [PATCH] arm: rpi: Device tree modifications for U-Boot Simon Glass <sjg@chromium.org> - 2015-08-11 16:30 +0200
    Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Lucas Stach <dev@lynxeye.de> - 2015-08-11 19:20 +0200
      Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Stephen Warren <swarren@wwwdotorg.org> - 2015-08-11 19:30 +0200
        Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Lucas Stach <dev@lynxeye.de> - 2015-08-11 21:40 +0200
      Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Simon Glass <sjg@chromium.org> - 2015-08-12 15:30 +0200
        Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Simon Glass <sjg@chromium.org> - 2015-08-14 20:40 +0200
          Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Rob Herring <robherring2@gmail.com> - 2015-08-14 22:30 +0200
            Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Simon Glass <sjg@chromium.org> - 2015-08-15 15:50 +0200
        Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Stephen Warren <swarren@wwwdotorg.org> - 2015-08-15 05:50 +0200
          Re: [PATCH] arm: rpi: Device tree modifications for U-Boot Simon Glass <sjg@chromium.org> - 2015-08-15 15:50 +0200

#1205178 — [PATCH] arm: rpi: Device tree modifications for U-Boot

This updates the device tree from the kernel version to something suitable
for U-Boot:

- Add stdout-path alias for console
- Mark the /soc node to be available pre-relocation so that the early
serial console works (we need the 'ranges' property to be available)

Signed-off-by: Simon Glass <sjg@chromium.org>
---

 arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
index 301c73f..bd6bff6 100644
--- a/arch/arm/boot/dts/bcm2835.dtsi
+++ b/arch/arm/boot/dts/bcm2835.dtsi
@@ -8,6 +8,7 @@
 
 	chosen {
 		bootargs = "earlyprintk console=ttyAMA0";
+		stdout-path = &uart;
 	};
 
 	soc {
@@ -16,6 +17,7 @@
 		#size-cells = <1>;
 		ranges = <0x7e000000 0x20000000 0x02000000>;
 		dma-ranges = <0x40000000 0x00000000 0x20000000>;
+		u-boot,dm-pre-reloc;
 
 		timer@7e003000 {
 			compatible = "brcm,bcm2835-system-timer";
@@ -92,7 +94,7 @@
 			#interrupt-cells = <2>;
 		};
 
-		uart@7e201000 {
+		uart: uart@7e201000 {
 			compatible = "brcm,bcm2835-pl011", "arm,pl011", "arm,primecell";
 			reg = <0x7e201000 0x1000>;
 			interrupts = <2 25>;
-- 
2.5.0.rc2.392.g76e840b

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#1205300

Hi Simon,

why did you send this to the Tegra ML?

Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
> This updates the device tree from the kernel version to something suitable
> for U-Boot:
> 
> - Add stdout-path alias for console
> - Mark the /soc node to be available pre-relocation so that the early
> serial console works (we need the 'ranges' property to be available)
> 
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
> 
>  arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
> index 301c73f..bd6bff6 100644
> --- a/arch/arm/boot/dts/bcm2835.dtsi
> +++ b/arch/arm/boot/dts/bcm2835.dtsi
> @@ -8,6 +8,7 @@
>  
>  	chosen {
>  		bootargs = "earlyprintk console=ttyAMA0";
> +		stdout-path = &uart;
>  	};
>  
>  	soc {
> @@ -16,6 +17,7 @@
>  		#size-cells = <1>;
>  		ranges = <0x7e000000 0x20000000 0x02000000>;
>  		dma-ranges = <0x40000000 0x00000000 0x20000000>;
> +		u-boot,dm-pre-reloc;

Why do you need this and why should upstream carry your favourite
bootloaders configuration? This is in no way hardware description.

Regards,
Lucas

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#1205305

On 08/11/2015 11:05 AM, Lucas Stach wrote:
> Hi Simon,
>
> why did you send this to the Tegra ML?

At my request, so that the DT changes could be reviewed by the kernel DT 
reviewers and added to the copy of the DT files in the kernel source 
tree if approved.

My assertion is that DT content should be independent of SW stack. Or 
put another way, all SW stacks should use the same DT content. As such, 
if these properties are needed by U-Boot, and contained in the copy of 
the DT files in the U-Boot source tree, they should also be present in 
the copy of the DT files in the kernel source tree, so the two do not 
become out of sync.

> Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
>> This updates the device tree from the kernel version to something suitable
>> for U-Boot:
>>
>> - Add stdout-path alias for console
>> - Mark the /soc node to be available pre-relocation so that the early
>> serial console works (we need the 'ranges' property to be available)

>> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
>> index 301c73f..bd6bff6 100644
>> --- a/arch/arm/boot/dts/bcm2835.dtsi
>> +++ b/arch/arm/boot/dts/bcm2835.dtsi
>> @@ -8,6 +8,7 @@
>>
>>   	chosen {
>>   		bootargs = "earlyprintk console=ttyAMA0";
>> +		stdout-path = &uart;
>>   	};
>>
>>   	soc {
>> @@ -16,6 +17,7 @@
>>   		#size-cells = <1>;
>>   		ranges = <0x7e000000 0x20000000 0x02000000>;
>>   		dma-ranges = <0x40000000 0x00000000 0x20000000>;
>> +		u-boot,dm-pre-reloc;
>
> Why do you need this and why should upstream carry your favourite
> bootloaders configuration? This is in no way hardware description.


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#1205399

Am Dienstag, den 11.08.2015, 11:29 -0600 schrieb Stephen Warren:
> On 08/11/2015 11:05 AM, Lucas Stach wrote:
> > Hi Simon,
> >
> > why did you send this to the Tegra ML?
> 
> At my request, so that the DT changes could be reviewed by the kernel DT 
> reviewers and added to the copy of the DT files in the kernel source 
> tree if approved.
> 
This doesn't really answer the question why it was sent to the Tegra
list if it is an RPi change, but that's just a side note.

> My assertion is that DT content should be independent of SW stack. Or 
> put another way, all SW stacks should use the same DT content. As such, 
> if these properties are needed by U-Boot, and contained in the copy of 
> the DT files in the U-Boot source tree, they should also be present in 
> the copy of the DT files in the kernel source tree, so the two do not 
> become out of sync.
> 
I agree with that overall goal to have a common DT base between
different software stacks. After all I lobbied for keeping the Tegra
pinctrl setting in the DT even though Linux doesn't use them any more.

For my question below I honestly want an answer as to why U-Boot needs
those DT changes and why it can't work with the current DT contents.
It's really just the same question we also have to answer for each and
every DT addition that we do for Linux.

Regards,
Lucas

> > Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
> >> This updates the device tree from the kernel version to something suitable
> >> for U-Boot:
> >>
> >> - Add stdout-path alias for console
> >> - Mark the /soc node to be available pre-relocation so that the early
> >> serial console works (we need the 'ranges' property to be available)
> 
> >> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
> >> index 301c73f..bd6bff6 100644
> >> --- a/arch/arm/boot/dts/bcm2835.dtsi
> >> +++ b/arch/arm/boot/dts/bcm2835.dtsi
> >> @@ -8,6 +8,7 @@
> >>
> >>   	chosen {
> >>   		bootargs = "earlyprintk console=ttyAMA0";
> >> +		stdout-path = &uart;
> >>   	};
> >>
> >>   	soc {
> >> @@ -16,6 +17,7 @@
> >>   		#size-cells = <1>;
> >>   		ranges = <0x7e000000 0x20000000 0x02000000>;
> >>   		dma-ranges = <0x40000000 0x00000000 0x20000000>;
> >> +		u-boot,dm-pre-reloc;
> >
> > Why do you need this and why should upstream carry your favourite
> > bootloaders configuration? This is in no way hardware description.
> 
> 


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#1206089

Hi Lucas,

On 11 August 2015 at 11:05, Lucas Stach <dev@lynxeye.de> wrote:
> Hi Simon,
>
> why did you send this to the Tegra ML?
>
> Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
>> This updates the device tree from the kernel version to something suitable
>> for U-Boot:
>>
>> - Add stdout-path alias for console
>> - Mark the /soc node to be available pre-relocation so that the early
>> serial console works (we need the 'ranges' property to be available)
>>
>> Signed-off-by: Simon Glass <sjg@chromium.org>
>> ---
>>
>>  arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
>> index 301c73f..bd6bff6 100644
>> --- a/arch/arm/boot/dts/bcm2835.dtsi
>> +++ b/arch/arm/boot/dts/bcm2835.dtsi
>> @@ -8,6 +8,7 @@
>>
>>       chosen {
>>               bootargs = "earlyprintk console=ttyAMA0";
>> +             stdout-path = &uart;
>>       };
>>
>>       soc {
>> @@ -16,6 +17,7 @@
>>               #size-cells = <1>;
>>               ranges = <0x7e000000 0x20000000 0x02000000>;
>>               dma-ranges = <0x40000000 0x00000000 0x20000000>;
>> +             u-boot,dm-pre-reloc;
>
> Why do you need this and why should upstream carry your favourite
> bootloaders configuration? This is in no way hardware description.

I'm not sure how much you know about U-Boot, so let me know if you
need more info.

U-Boot normally starts up by setting up its serial UART and displaying
a banner message. At this stage typically only a few devices are
initialised (e.g. maybe just the UART). It then relocates itself to
the top of memory and starts up all the devices. It throws away any
previous devices that it set up before relocation and starts again.

U-Boot uses a thing called driver model (dm) which handles driver
binding and probing. Driver model has the device tree and would
normally scan through it and create devices for everything it finds.

Before relocation we don't need every device. Also the CPU is often
running slowly, perhaps without the cache enabled. SDRAM may not be
available yet so space is short. We want to avoid starting up things
that will not be used.

So this property indicates that the device is needed before relocation
and should be set up by driver model. We need it to avoid a very slow
and memory-hungry startup.

As to why upstream should accept it, my understanding of upstream is
that people can send patches to it and in fact are encouraged to do
so, to avoid misunderstandings and duplication. The device tree files
are stored in Linux so any binding or source file changes should end
up there. Otherwise the files tend to diverge and we end up with
multiple bindings and multiple versions of the same source file.

Regards,
Simon
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#1207847

-linux-tegra

Hi,

On 12 August 2015 at 07:21, Simon Glass <sjg@chromium.org> wrote:
> Hi Lucas,
>
> On 11 August 2015 at 11:05, Lucas Stach <dev@lynxeye.de> wrote:
>> Hi Simon,
>>
>> why did you send this to the Tegra ML?
>>
>> Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
>>> This updates the device tree from the kernel version to something suitable
>>> for U-Boot:
>>>
>>> - Add stdout-path alias for console
>>> - Mark the /soc node to be available pre-relocation so that the early
>>> serial console works (we need the 'ranges' property to be available)
>>>
>>> Signed-off-by: Simon Glass <sjg@chromium.org>
>>> ---
>>>
>>>  arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
>>> index 301c73f..bd6bff6 100644
>>> --- a/arch/arm/boot/dts/bcm2835.dtsi
>>> +++ b/arch/arm/boot/dts/bcm2835.dtsi
>>> @@ -8,6 +8,7 @@
>>>
>>>       chosen {
>>>               bootargs = "earlyprintk console=ttyAMA0";
>>> +             stdout-path = &uart;
>>>       };
>>>
>>>       soc {
>>> @@ -16,6 +17,7 @@
>>>               #size-cells = <1>;
>>>               ranges = <0x7e000000 0x20000000 0x02000000>;
>>>               dma-ranges = <0x40000000 0x00000000 0x20000000>;
>>> +             u-boot,dm-pre-reloc;
>>
>> Why do you need this and why should upstream carry your favourite
>> bootloaders configuration? This is in no way hardware description.
>
> I'm not sure how much you know about U-Boot, so let me know if you
> need more info.
>
> U-Boot normally starts up by setting up its serial UART and displaying
> a banner message. At this stage typically only a few devices are
> initialised (e.g. maybe just the UART). It then relocates itself to
> the top of memory and starts up all the devices. It throws away any
> previous devices that it set up before relocation and starts again.
>
> U-Boot uses a thing called driver model (dm) which handles driver
> binding and probing. Driver model has the device tree and would
> normally scan through it and create devices for everything it finds.
>
> Before relocation we don't need every device. Also the CPU is often
> running slowly, perhaps without the cache enabled. SDRAM may not be
> available yet so space is short. We want to avoid starting up things
> that will not be used.
>
> So this property indicates that the device is needed before relocation
> and should be set up by driver model. We need it to avoid a very slow
> and memory-hungry startup.
>
> As to why upstream should accept it, my understanding of upstream is
> that people can send patches to it and in fact are encouraged to do
> so, to avoid misunderstandings and duplication. The device tree files
> are stored in Linux so any binding or source file changes should end
> up there. Otherwise the files tend to diverge and we end up with
> multiple bindings and multiple versions of the same source file.

Is the above explanation sufficient? Will this patch be applied?

Regards,
Simon
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#1207893

On Fri, Aug 14, 2015 at 1:34 PM, Simon Glass <sjg@chromium.org> wrote:
> -linux-tegra
>
> Hi,
>
> On 12 August 2015 at 07:21, Simon Glass <sjg@chromium.org> wrote:
>> Hi Lucas,
>>
>> On 11 August 2015 at 11:05, Lucas Stach <dev@lynxeye.de> wrote:
>>> Hi Simon,
>>>
>>> why did you send this to the Tegra ML?
>>>
>>> Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
>>>> This updates the device tree from the kernel version to something suitable
>>>> for U-Boot:
>>>>
>>>> - Add stdout-path alias for console
>>>> - Mark the /soc node to be available pre-relocation so that the early
>>>> serial console works (we need the 'ranges' property to be available)

I find it quite strange that you must explicitly enable the parent
node, but not the uart node.

>>>>
>>>> Signed-off-by: Simon Glass <sjg@chromium.org>
>>>> ---
>>>>
>>>>  arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
>>>> index 301c73f..bd6bff6 100644
>>>> --- a/arch/arm/boot/dts/bcm2835.dtsi
>>>> +++ b/arch/arm/boot/dts/bcm2835.dtsi
>>>> @@ -8,6 +8,7 @@
>>>>
>>>>       chosen {
>>>>               bootargs = "earlyprintk console=ttyAMA0";
>>>> +             stdout-path = &uart;
>>>>       };
>>>>
>>>>       soc {
>>>> @@ -16,6 +17,7 @@
>>>>               #size-cells = <1>;
>>>>               ranges = <0x7e000000 0x20000000 0x02000000>;
>>>>               dma-ranges = <0x40000000 0x00000000 0x20000000>;
>>>> +             u-boot,dm-pre-reloc;
>>>
>>> Why do you need this and why should upstream carry your favourite
>>> bootloaders configuration? This is in no way hardware description.
>>
>> I'm not sure how much you know about U-Boot, so let me know if you
>> need more info.
>>
>> U-Boot normally starts up by setting up its serial UART and displaying
>> a banner message. At this stage typically only a few devices are
>> initialised (e.g. maybe just the UART). It then relocates itself to
>> the top of memory and starts up all the devices. It throws away any
>> previous devices that it set up before relocation and starts again.
>>
>> U-Boot uses a thing called driver model (dm) which handles driver
>> binding and probing. Driver model has the device tree and would
>> normally scan through it and create devices for everything it finds.

How do you debug the DM itself? It seems like you still would need
something earlier for debug like earlycon in the kernel. u-boot DM is
probably simple enough you can get away with using it early, but you
often can't as the complexity increases. Ultimately you need something
simple that just hits all the registers needed to get characters out.
What happens when you add pinmux, clocks, PMIC, power domains, etc. to
the DM and they all become dependencies for the UART?

>> Before relocation we don't need every device. Also the CPU is often
>> running slowly, perhaps without the cache enabled. SDRAM may not be
>> available yet so space is short. We want to avoid starting up things
>> that will not be used.
>>
>> So this property indicates that the device is needed before relocation
>> and should be set up by driver model. We need it to avoid a very slow
>> and memory-hungry startup.

Can't the need for that property change over time? Either as more
drivers are converted to DM you need to add this or you add some
feature that depends on a driver (e.g. get a board rev or boot mode
from GPIO). You would have backwards compatibility issues with this.
I'm somewhat less worried about that for u-boot as we should be
bundling the dtb and bootloader rather than kernel and dtb. For the
UART, you can just get which UART to initialize early from
stdout-path. But for other cases, couldn't you just have the platform
provide the list of needed drivers. Then when u-boot needs change, you
just change u-boot.

>> As to why upstream should accept it, my understanding of upstream is
>> that people can send patches to it and in fact are encouraged to do
>> so, to avoid misunderstandings and duplication. The device tree files
>> are stored in Linux so any binding or source file changes should end
>> up there. Otherwise the files tend to diverge and we end up with
>> multiple bindings and multiple versions of the same source file.
>
> Is the above explanation sufficient? Will this patch be applied?

Well, for starters bindings need to be documented, so you need to send
this as a binding doc with this detail.

Rob
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#1208087

Hi Rob,

On 14 August 2015 at 14:29, Rob Herring <robherring2@gmail.com> wrote:
> On Fri, Aug 14, 2015 at 1:34 PM, Simon Glass <sjg@chromium.org> wrote:
>> -linux-tegra
>>
>> Hi,
>>
>> On 12 August 2015 at 07:21, Simon Glass <sjg@chromium.org> wrote:
>>> Hi Lucas,
>>>
>>> On 11 August 2015 at 11:05, Lucas Stach <dev@lynxeye.de> wrote:
>>>> Hi Simon,
>>>>
>>>> why did you send this to the Tegra ML?
>>>>
>>>> Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
>>>>> This updates the device tree from the kernel version to something suitable
>>>>> for U-Boot:
>>>>>
>>>>> - Add stdout-path alias for console
>>>>> - Mark the /soc node to be available pre-relocation so that the early
>>>>> serial console works (we need the 'ranges' property to be available)
>
> I find it quite strange that you must explicitly enable the parent
> node, but not the uart node.

U-Boot tries hard to find and bind the UART using the stdout-path
link. I would like to add it in the UART node also but we were able to
work around it so far.

>
>>>>>
>>>>> Signed-off-by: Simon Glass <sjg@chromium.org>
>>>>> ---
>>>>>
>>>>>  arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
>>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
>>>>> index 301c73f..bd6bff6 100644
>>>>> --- a/arch/arm/boot/dts/bcm2835.dtsi
>>>>> +++ b/arch/arm/boot/dts/bcm2835.dtsi
>>>>> @@ -8,6 +8,7 @@
>>>>>
>>>>>       chosen {
>>>>>               bootargs = "earlyprintk console=ttyAMA0";
>>>>> +             stdout-path = &uart;
>>>>>       };
>>>>>
>>>>>       soc {
>>>>> @@ -16,6 +17,7 @@
>>>>>               #size-cells = <1>;
>>>>>               ranges = <0x7e000000 0x20000000 0x02000000>;
>>>>>               dma-ranges = <0x40000000 0x00000000 0x20000000>;
>>>>> +             u-boot,dm-pre-reloc;
>>>>
>>>> Why do you need this and why should upstream carry your favourite
>>>> bootloaders configuration? This is in no way hardware description.
>>>
>>> I'm not sure how much you know about U-Boot, so let me know if you
>>> need more info.
>>>
>>> U-Boot normally starts up by setting up its serial UART and displaying
>>> a banner message. At this stage typically only a few devices are
>>> initialised (e.g. maybe just the UART). It then relocates itself to
>>> the top of memory and starts up all the devices. It throws away any
>>> previous devices that it set up before relocation and starts again.
>>>
>>> U-Boot uses a thing called driver model (dm) which handles driver
>>> binding and probing. Driver model has the device tree and would
>>> normally scan through it and create devices for everything it finds.
>
> How do you debug the DM itself? It seems like you still would need
> something earlier for debug like earlycon in the kernel. u-boot DM is
> probably simple enough you can get away with using it early, but you
> often can't as the complexity increases. Ultimately you need something
> simple that just hits all the registers needed to get characters out.
> What happens when you add pinmux, clocks, PMIC, power domains, etc. to
> the DM and they all become dependencies for the UART?

This doesn't seem like a device tree binding question but let me try
to answer it.

This is a problem - one of the challenges of driver model is that the
UART gets further away from the reset vector.

In U-Boot there is a single debug UART which can be supported by the
various serial drivers (only one can be selected on each platform).
There is a special debug_uart_init() function which is supposed to set
up the UART for that platform. After that, and until driver model UART
is up, console output can go through the debug UART.

>
>>> Before relocation we don't need every device. Also the CPU is often
>>> running slowly, perhaps without the cache enabled. SDRAM may not be
>>> available yet so space is short. We want to avoid starting up things
>>> that will not be used.
>>>
>>> So this property indicates that the device is needed before relocation
>>> and should be set up by driver model. We need it to avoid a very slow
>>> and memory-hungry startup.
>
> Can't the need for that property change over time? Either as more
> drivers are converted to DM you need to add this or you add some
> feature that depends on a driver (e.g. get a board rev or boot mode
> from GPIO). You would have backwards compatibility issues with this.
> I'm somewhat less worried about that for u-boot as we should be
> bundling the dtb and bootloader rather than kernel and dtb. For the
> UART, you can just get which UART to initialize early from
> stdout-path. But for other cases, couldn't you just have the platform
> provide the list of needed drivers. Then when u-boot needs change, you
> just change u-boot.

Yes U-Boot and its device tree are normally built from the same tree
at the same time. We don't expect to have to support an older or newer
device tree with the same U-Boot binary. So I don't see a problem
here.

The UART should have as few dependencies as possible. But if the
particular platform needs to check a GPIO to find out the UART number
(i.e. stdout-path cannot be used) then we would need to support that
case. It hasn't come up yet but it might. I certainly see platforms
where we need some other nodes before relocation and would like to
mark them as such. But I hope that for UART we can generally use
stdout-path.

The list of drivers doesn't help that much. What would I do with such
a list, and where would I keep such platform-specific information
other than in the device tree? It seems much simpler to hold the
information about what the platform needs to get through early boot in
one place. Then we have just a few lines of generic code to deal with
it.

>
>>> As to why upstream should accept it, my understanding of upstream is
>>> that people can send patches to it and in fact are encouraged to do
>>> so, to avoid misunderstandings and duplication. The device tree files
>>> are stored in Linux so any binding or source file changes should end
>>> up there. Otherwise the files tend to diverge and we end up with
>>> multiple bindings and multiple versions of the same source file.
>>
>> Is the above explanation sufficient? Will this patch be applied?
>
> Well, for starters bindings need to be documented, so you need to send
> this as a binding doc with this detail.

OK I'll update the patch and resend it.

Regards.
Simon
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#1208000

On 08/12/2015 07:21 AM, Simon Glass wrote:
> Hi Lucas,
> 
> On 11 August 2015 at 11:05, Lucas Stach <dev@lynxeye.de> wrote:
>> Hi Simon,
>>
>> why did you send this to the Tegra ML?
>>
>> Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
>>> This updates the device tree from the kernel version to something suitable
>>> for U-Boot:
>>>
>>> - Add stdout-path alias for console
>>> - Mark the /soc node to be available pre-relocation so that the early
>>> serial console works (we need the 'ranges' property to be available)
>>>
>>> Signed-off-by: Simon Glass <sjg@chromium.org>
>>> ---
>>>
>>>  arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
>>> index 301c73f..bd6bff6 100644
>>> --- a/arch/arm/boot/dts/bcm2835.dtsi
>>> +++ b/arch/arm/boot/dts/bcm2835.dtsi
>>> @@ -8,6 +8,7 @@
>>>
>>>       chosen {
>>>               bootargs = "earlyprintk console=ttyAMA0";
>>> +             stdout-path = &uart;
>>>       };
>>>
>>>       soc {
>>> @@ -16,6 +17,7 @@
>>>               #size-cells = <1>;
>>>               ranges = <0x7e000000 0x20000000 0x02000000>;
>>>               dma-ranges = <0x40000000 0x00000000 0x20000000>;
>>> +             u-boot,dm-pre-reloc;
>>
>> Why do you need this and why should upstream carry your favourite
>> bootloaders configuration? This is in no way hardware description.
> 
> I'm not sure how much you know about U-Boot, so let me know if you
> need more info.
> 
> U-Boot normally starts up by setting up its serial UART and displaying
> a banner message. At this stage typically only a few devices are
> initialised (e.g. maybe just the UART). It then relocates itself to
> the top of memory and starts up all the devices. It throws away any
> previous devices that it set up before relocation and starts again.
> 
> U-Boot uses a thing called driver model (dm) which handles driver
> binding and probing. Driver model has the device tree and would
> normally scan through it and create devices for everything it finds.
> 
> Before relocation we don't need every device. Also the CPU is often
> running slowly, perhaps without the cache enabled. SDRAM may not be
> available yet so space is short. We want to avoid starting up things
> that will not be used.
> 
> So this property indicates that the device is needed before relocation
> and should be set up by driver model. We need it to avoid a very slow
> and memory-hungry startup.
> 
> As to why upstream should accept it, my understanding of upstream is
> that people can send patches to it and in fact are encouraged to do
> so, to avoid misunderstandings and duplication. The device tree files
> are stored in Linux so any binding or source file changes should end
> up there. Otherwise the files tend to diverge and we end up with
> multiple bindings and multiple versions of the same source file.

On many platforms, we have U-Boot SPL running first, then the main
U-Boot. The main U-Boot binary contains both the code to do the
relocation and the binary that runs after relocation. It seems like it'd
be simpler to split these up into 3 binaries that each do a single job:

1) SPL, roughly as-is today (varying jobs depending on platform)

2) Relocator, which does nothing but work out where to copy U-Boot,
memcpy()s it there, relocates the image (if not PIE), and jumps to it.

3) The main U-Boot.

Item (2) above should be simple enough that it can use a very simple
debug mechanism rather like DEBUG_LL in the Linux kernel. Similar to
what Rob mentioned in his email.

Item (3) could use DM and DT/ACPI/... to get device information in a
complete non-hard-coded manner.
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#1208085

Hi Stephen,

On 14 August 2015 at 21:46, Stephen Warren <swarren@wwwdotorg.org> wrote:
> On 08/12/2015 07:21 AM, Simon Glass wrote:
>> Hi Lucas,
>>
>> On 11 August 2015 at 11:05, Lucas Stach <dev@lynxeye.de> wrote:
>>> Hi Simon,
>>>
>>> why did you send this to the Tegra ML?
>>>
>>> Am Dienstag, den 11.08.2015, 08:25 -0600 schrieb Simon Glass:
>>>> This updates the device tree from the kernel version to something suitable
>>>> for U-Boot:
>>>>
>>>> - Add stdout-path alias for console
>>>> - Mark the /soc node to be available pre-relocation so that the early
>>>> serial console works (we need the 'ranges' property to be available)
>>>>
>>>> Signed-off-by: Simon Glass <sjg@chromium.org>
>>>> ---
>>>>
>>>>  arch/arm/boot/dts/bcm2835.dtsi | 4 +++-
>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi
>>>> index 301c73f..bd6bff6 100644
>>>> --- a/arch/arm/boot/dts/bcm2835.dtsi
>>>> +++ b/arch/arm/boot/dts/bcm2835.dtsi
>>>> @@ -8,6 +8,7 @@
>>>>
>>>>       chosen {
>>>>               bootargs = "earlyprintk console=ttyAMA0";
>>>> +             stdout-path = &uart;
>>>>       };
>>>>
>>>>       soc {
>>>> @@ -16,6 +17,7 @@
>>>>               #size-cells = <1>;
>>>>               ranges = <0x7e000000 0x20000000 0x02000000>;
>>>>               dma-ranges = <0x40000000 0x00000000 0x20000000>;
>>>> +             u-boot,dm-pre-reloc;
>>>
>>> Why do you need this and why should upstream carry your favourite
>>> bootloaders configuration? This is in no way hardware description.
>>
>> I'm not sure how much you know about U-Boot, so let me know if you
>> need more info.
>>
>> U-Boot normally starts up by setting up its serial UART and displaying
>> a banner message. At this stage typically only a few devices are
>> initialised (e.g. maybe just the UART). It then relocates itself to
>> the top of memory and starts up all the devices. It throws away any
>> previous devices that it set up before relocation and starts again.
>>
>> U-Boot uses a thing called driver model (dm) which handles driver
>> binding and probing. Driver model has the device tree and would
>> normally scan through it and create devices for everything it finds.
>>
>> Before relocation we don't need every device. Also the CPU is often
>> running slowly, perhaps without the cache enabled. SDRAM may not be
>> available yet so space is short. We want to avoid starting up things
>> that will not be used.
>>
>> So this property indicates that the device is needed before relocation
>> and should be set up by driver model. We need it to avoid a very slow
>> and memory-hungry startup.
>>
>> As to why upstream should accept it, my understanding of upstream is
>> that people can send patches to it and in fact are encouraged to do
>> so, to avoid misunderstandings and duplication. The device tree files
>> are stored in Linux so any binding or source file changes should end
>> up there. Otherwise the files tend to diverge and we end up with
>> multiple bindings and multiple versions of the same source file.
>
> On many platforms, we have U-Boot SPL running first, then the main
> U-Boot. The main U-Boot binary contains both the code to do the
> relocation and the binary that runs after relocation. It seems like it'd
> be simpler to split these up into 3 binaries that each do a single job:
>
> 1) SPL, roughly as-is today (varying jobs depending on platform)
>
> 2) Relocator, which does nothing but work out where to copy U-Boot,
> memcpy()s it there, relocates the image (if not PIE), and jumps to it.
>
> 3) The main U-Boot.
>
> Item (2) above should be simple enough that it can use a very simple
> debug mechanism rather like DEBUG_LL in the Linux kernel. Similar to
> what Rob mentioned in his email.
>
> Item (3) could use DM and DT/ACPI/... to get device information in a
> complete non-hard-coded manner.

This comment does no seem to relate to my patch. We could certainly
re-architect U-Boot to work this way. There are  lot of reasons why
U-Boot works as it does and many platforms don't have SPL.

Relating what you said to the current U-Boot, your item (2) is
analogous to us not setting up driver model before relocation at all,
and just having a debug UART. That's a huge topic though, well beyond
the scope of my original patch. I think it would be better for you to
start a thread on the U-Boot mailing list with your proposal. At least
on x86 (which has no SPL) there are all sorts of things that currently
happen before relocation.

Regards,
Simon
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