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Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power

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  Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power Ludovic Desroches <ludovic.desroches@atmel.com> - 2015-11-24 10:30 +0100
    Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power Ulf Hansson <ulf.hansson@linaro.org> - 2015-11-24 12:10 +0100
      Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power Ludovic Desroches <ludovic.desroches@atmel.com> - 2015-11-24 14:20 +0100
        Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power Ulf Hansson <ulf.hansson@linaro.org> - 2015-11-24 15:00 +0100
          Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power Ludovic Desroches <ludovic.desroches@atmel.com> - 2015-11-24 15:10 +0100
            Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power Ulf Hansson <ulf.hansson@linaro.org> - 2015-11-24 16:20 +0100

#1276188 — Re: [PATCH 1/2] mmc: sdhci: set bus voltage before enabling bus power

Hi Ulf,

On Mon, Nov 09, 2015 at 05:30:26PM +0100, Ludovic Desroches wrote:
> On Mon, Nov 09, 2015 at 05:00:46PM +0100, Ulf Hansson wrote:

[...]

> > Now, this discussion was interesting, but I forgot what problem you
> > actually where trying to solve? :-)
> 
> There is this discussion because of two things:
> - Fixing something I consider as a bug: when I have a VMMC, only
>   setting/clearing bit 0. Our controller strictly obeys to the spec and
>   check the 'SD Bus Voltage Select' field. Since we put a reserved value
>   (000), the Power On is not performed.
> - I was trying to get help to understand what is this 'SD Bus Voltage'.
>   For our controller and sdhci_set_power(), it seems to stand for VMMC.
>   For me, everything concerning bus voltage is related to VQMMC, so I was
>   disappointed.

Do you plan to take the patch for VMMC? If yes, I will send a new patch
for the device tree (I'll only add vmmc, not vqmmc as discussed); if
not, forget these two patches.

Regards

Ludovic
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#1276322

On 24 November 2015 at 10:23, Ludovic Desroches
<ludovic.desroches@atmel.com> wrote:
> Hi Ulf,
>
> On Mon, Nov 09, 2015 at 05:30:26PM +0100, Ludovic Desroches wrote:
>> On Mon, Nov 09, 2015 at 05:00:46PM +0100, Ulf Hansson wrote:
>
> [...]
>
>> > Now, this discussion was interesting, but I forgot what problem you
>> > actually where trying to solve? :-)
>>
>> There is this discussion because of two things:
>> - Fixing something I consider as a bug: when I have a VMMC, only
>>   setting/clearing bit 0. Our controller strictly obeys to the spec and
>>   check the 'SD Bus Voltage Select' field. Since we put a reserved value
>>   (000), the Power On is not performed.
>> - I was trying to get help to understand what is this 'SD Bus Voltage'.
>>   For our controller and sdhci_set_power(), it seems to stand for VMMC.
>>   For me, everything concerning bus voltage is related to VQMMC, so I was
>>   disappointed.
>
> Do you plan to take the patch for VMMC? If yes, I will send a new patch
> for the device tree (I'll only add vmmc, not vqmmc as discussed); if
> not, forget these two patches.
>

Which patch do you refer to for "VMMC"?

Kind regards
Uffe
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#1276429

On Tue, Nov 24, 2015 at 12:01:53PM +0100, Ulf Hansson wrote:
> On 24 November 2015 at 10:23, Ludovic Desroches
> <ludovic.desroches@atmel.com> wrote:
> > Hi Ulf,
> >
> > On Mon, Nov 09, 2015 at 05:30:26PM +0100, Ludovic Desroches wrote:
> >> On Mon, Nov 09, 2015 at 05:00:46PM +0100, Ulf Hansson wrote:
> >
> > [...]
> >
> >> > Now, this discussion was interesting, but I forgot what problem you
> >> > actually where trying to solve? :-)
> >>
> >> There is this discussion because of two things:
> >> - Fixing something I consider as a bug: when I have a VMMC, only
> >>   setting/clearing bit 0. Our controller strictly obeys to the spec and
> >>   check the 'SD Bus Voltage Select' field. Since we put a reserved value
> >>   (000), the Power On is not performed.
> >> - I was trying to get help to understand what is this 'SD Bus Voltage'.
> >>   For our controller and sdhci_set_power(), it seems to stand for VMMC.
> >>   For me, everything concerning bus voltage is related to VQMMC, so I was
> >>   disappointed.
> >
> > Do you plan to take the patch for VMMC? If yes, I will send a new patch
> > for the device tree (I'll only add vmmc, not vqmmc as discussed); if
> > not, forget these two patches.
> >
> 
> Which patch do you refer to for "VMMC"?
> 

This one to not write an invalid voltage in the power control register
even if we have an external regulator for vmmc.

Regards

Ludovic
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#1276493

On 24 November 2015 at 14:12, Ludovic Desroches
<ludovic.desroches@atmel.com> wrote:
> On Tue, Nov 24, 2015 at 12:01:53PM +0100, Ulf Hansson wrote:
>> On 24 November 2015 at 10:23, Ludovic Desroches
>> <ludovic.desroches@atmel.com> wrote:
>> > Hi Ulf,
>> >
>> > On Mon, Nov 09, 2015 at 05:30:26PM +0100, Ludovic Desroches wrote:
>> >> On Mon, Nov 09, 2015 at 05:00:46PM +0100, Ulf Hansson wrote:
>> >
>> > [...]
>> >
>> >> > Now, this discussion was interesting, but I forgot what problem you
>> >> > actually where trying to solve? :-)
>> >>
>> >> There is this discussion because of two things:
>> >> - Fixing something I consider as a bug: when I have a VMMC, only
>> >>   setting/clearing bit 0. Our controller strictly obeys to the spec and
>> >>   check the 'SD Bus Voltage Select' field. Since we put a reserved value
>> >>   (000), the Power On is not performed.
>> >> - I was trying to get help to understand what is this 'SD Bus Voltage'.
>> >>   For our controller and sdhci_set_power(), it seems to stand for VMMC.
>> >>   For me, everything concerning bus voltage is related to VQMMC, so I was
>> >>   disappointed.
>> >
>> > Do you plan to take the patch for VMMC? If yes, I will send a new patch
>> > for the device tree (I'll only add vmmc, not vqmmc as discussed); if
>> > not, forget these two patches.
>> >
>>
>> Which patch do you refer to for "VMMC"?
>>
>
> This one to not write an invalid voltage in the power control register
> even if we have an external regulator for vmmc.
>

As I stated earlier, according to the SDHCI spec in the section for
the Power Control Register. Bit 0 needs to be set when communicating
with the card as it will for
example enable the clock.

I suspect if I apply your patch several sdhci variants would break,
don't you think?

Kind regards
Uffe
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#1276504

On Tue, Nov 24, 2015 at 02:56:21PM +0100, Ulf Hansson wrote:
> On 24 November 2015 at 14:12, Ludovic Desroches
> <ludovic.desroches@atmel.com> wrote:
> > On Tue, Nov 24, 2015 at 12:01:53PM +0100, Ulf Hansson wrote:
> >> On 24 November 2015 at 10:23, Ludovic Desroches
> >> <ludovic.desroches@atmel.com> wrote:
> >> > Hi Ulf,
> >> >
> >> > On Mon, Nov 09, 2015 at 05:30:26PM +0100, Ludovic Desroches wrote:
> >> >> On Mon, Nov 09, 2015 at 05:00:46PM +0100, Ulf Hansson wrote:
> >> >
> >> > [...]
> >> >
> >> >> > Now, this discussion was interesting, but I forgot what problem you
> >> >> > actually where trying to solve? :-)
> >> >>
> >> >> There is this discussion because of two things:
> >> >> - Fixing something I consider as a bug: when I have a VMMC, only
> >> >>   setting/clearing bit 0. Our controller strictly obeys to the spec and
> >> >>   check the 'SD Bus Voltage Select' field. Since we put a reserved value
> >> >>   (000), the Power On is not performed.
> >> >> - I was trying to get help to understand what is this 'SD Bus Voltage'.
> >> >>   For our controller and sdhci_set_power(), it seems to stand for VMMC.
> >> >>   For me, everything concerning bus voltage is related to VQMMC, so I was
> >> >>   disappointed.
> >> >
> >> > Do you plan to take the patch for VMMC? If yes, I will send a new patch
> >> > for the device tree (I'll only add vmmc, not vqmmc as discussed); if
> >> > not, forget these two patches.
> >> >
> >>
> >> Which patch do you refer to for "VMMC"?
> >>
> >
> > This one to not write an invalid voltage in the power control register
> > even if we have an external regulator for vmmc.
> >
> 
> As I stated earlier, according to the SDHCI spec in the section for
> the Power Control Register. Bit 0 needs to be set when communicating
> with the card as it will for
> example enable the clock.
> 

I am okay with bit 0. I don't want to change this part, it will be done
later in sdhci_set_power(). My concern is only about bit 3-1, I want to
go through the switch statement.

> I suspect if I apply your patch several sdhci variants would break,
> don't you think?

I wouldn't sign it with my blood but I don't think so. It seems they
don't care about the SD bus Voltage since they work with an unsupported
voltage.

Regards

Ludovic
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#1276564

[...]

>> > This one to not write an invalid voltage in the power control register
>> > even if we have an external regulator for vmmc.
>> >
>>
>> As I stated earlier, according to the SDHCI spec in the section for
>> the Power Control Register. Bit 0 needs to be set when communicating
>> with the card as it will for
>> example enable the clock.
>>
>
> I am okay with bit 0. I don't want to change this part, it will be done
> later in sdhci_set_power(). My concern is only about bit 3-1, I want to
> go through the switch statement.

For those variants that have a VMMC and don't care about the other
bits (1->3), it means executing code that isn't needed.

Instead, as I have been telling people several times by now, let's
convert the "sdhci core" into a library, so each variant can pick and
do what suite them best.

>
>> I suspect if I apply your patch several sdhci variants would break,
>> don't you think?
>
> I wouldn't sign it with my blood but I don't think so. It seems they
> don't care about the SD bus Voltage since they work with an unsupported
> voltage.

You may very well be right, that it doesn't break anything. But in
this case I really don't want to take the risk.

As stated above, the proper solution would be that sdhci_set_power()
should be split up in smaller pieces, where each piece may become a
library function. Each host variant can then decide what to use.

Future wise, that would mean when changing a library function, it will
affect the subset of the sdhci variants that actually use it and not
*all* sdhci variants. Moreover it will lead to optimized code.

Kind regards
Uffe
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