linux-kernel - Re: [PATCH v2] mmc: sdhci: apply voltage range check only for non-fixed regulators

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Date:	Tue, 13 Nov 2012 09:14:18 -0500
From:	Chris Ball <cjb@...top.org>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>, Philip Rakity <prakity@...dia.com>
Subject: Re: [PATCH v2] mmc: sdhci: apply voltage range check only for non-fixed regulators

Hi,

On Tue, Nov 13 2012, Marek Szyprowski wrote:
>> On Tue, Nov 13 2012, Marek Szyprowski wrote:
>> > Fixed regulators cannot change their voltage, so disable all voltage
>> > range checking for them, otherwise the driver fails to operate with
>> > fixed regulators. Up to now it worked only by luck, because
>> > regulator_is_supported_voltage() function returned incorrect values.
>> > Commit "regulator: fix voltage check in regulator_is_supported_voltage()"
>> > fixed that function and now additional check is needed for fixed
>> > regulators.
>> >
>> > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>> > ---
>> >  drivers/mmc/host/sdhci.c |    2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> > index c7851c0..6f6534e 100644
>> > --- a/drivers/mmc/host/sdhci.c
>> > +++ b/drivers/mmc/host/sdhci.c
>> > @@ -2923,7 +2923,7 @@ int sdhci_add_host(struct sdhci_host *host)
>> >  		regulator_enable(host->vmmc);
>> >
>> >  #ifdef CONFIG_REGULATOR
>> > -	if (host->vmmc) {
>> > +	if (host->vmmc && regulator_count_voltages(host->vmmc) > 1) {
>> >  		ret = regulator_is_supported_voltage(host->vmmc, 3300000,
>> >  			3300000);
>> >  		if ((ret <= 0) || (!(caps[0] & SDHCI_CAN_VDD_330)))
>>
>> Thanks for the longer explanation.  I'm still missing something, though;
>> what's wrong with running the check as it was with the new regulator code?
>> (I haven't tried it yet.)
>>
>> #ifdef CONFIG_REGULATOR
>>          if (host->vmmc) {
>>                  ret = regulator_is_supported_voltage(host->vmmc, 3300000,
>>                          3300000);
>>                  if ((ret <= 0) || (!(caps[0] & SDHCI_CAN_VDD_330)))
>>                          caps[0] &= ~SDHCI_CAN_VDD_330;
>>                  ret = regulator_is_supported_voltage(host->vmmc, 3000000,
>>                          3000000);
>>                  if ((ret <= 0) || (!(caps[0] & SDHCI_CAN_VDD_300)))
>>                          caps[0] &= ~SDHCI_CAN_VDD_300;
>>                  ret = regulator_is_supported_voltage(host->vmmc, 1800000,
>>                          1800000);
>>                  if ((ret <= 0) || (!(caps[0] & SDHCI_CAN_VDD_180)))
>>                          caps[0] &= ~SDHCI_CAN_VDD_180;
>>          }
>> #endif /* CONFIG_REGULATOR */
>>
>> The point is to remove unsupported voltages, so if someone sets up a
>> fixed regulator at 3300000, all of the other caps are disabled.  Why
>> wouldn't that work without this change, and how are we supposed to
>> remove those caps on a fixed regulator after your patchset?
>>
>> Thanks, sorry if I'm missing something obvious,
>
> On our boards eMMC is connected to fixed 2.8V regulator, what results in
> clearing all available voltages and fail. The same situation is when one
> enable dummy regulator and try to use sdhci with it. My patch fixes this
> and restores sdhci to working state as it was before (before fixing
> regulator regulator_is_supported_voltage() function and earlier when
> MMC_BROKEN_VOLATGE capability was used).

I see.  Sounds like a separate bug -- Philip (or anyone else), any
idea how we should be treating eMMCs with a fixed voltage here?

Thanks,

- Chris.
-- 
Chris Ball   <cjb@...top.org>   <http://printf.net/>
One Laptop Per Child
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