Re: FW: [PATCH v2] mmc: sdhci: apply voltage range check only fornon-fixed regulators

From: Marek Szyprowski
Date: Tue Nov 20 2012 - 10:02:33 EST

Hello,

On 11/20/2012 3:14 PM, Kevin Liu wrote:
2012/11/20 Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>:
> Hello,
>
>
> On 11/20/2012 12:36 PM, Kevin Liu wrote:
>>
>> 2012/11/20 Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>:
>> > On 11/20/2012 9:59 AM, Kevin Liu wrote:
>> >> 2012/11/20 Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>:
>> >> > On 11/14/2012 8:11 AM, Kevin Liu wrote:
>> >> >>
>> >> >> > From: linux-mmc-owner@xxxxxxxxxxxxxxx
>> >> >> > [mailto:linux-mmc-owner@xxxxxxxxxxxxxxx] On Behalf Of Chris Ball
>> >> >> > Sent: Tuesday, November 13, 2012 10:14 PM
>> >> >> > To: Marek Szyprowski
>> >> >> > Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mmc@xxxxxxxxxxxxxxx;
>> >> >> > Kyungmin
>> >> >> > Park; Mark Brown; Liam Girdwood; Philip Rakity
>> >> >> > Subject: Re: [PATCH v2] mmc: sdhci: apply voltage range check only
>> >> >> > for non-fixed regulators
>> >> >> > 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@xxxxxxxxxxx>
>> >> >> >>> > ---
>> >> >> >>> > 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?
>> >> >> >
>> >> >>
>> >> >> I think we should check the voltage range rather than the voltage
>> >> >> point accoring to the spec.
>> >> >> Otherwise some valid voltage like 2.8v will be discarded by mistake.
>> >> >> My below old patch aim to fix this issue.
>> >> >> How do you think?
>> >> >>
>> >> >> -----Original Message-----
>> >> >> From: Kevin Liu [mailto:keyuan.liu@xxxxxxxxx]
>> >> >> Sent: Friday, September 28, 2012 3:56 PM
>> >> >> To: linux-mmc@xxxxxxxxxxxxxxx; cjb@xxxxxxxxxx; pierre@xxxxxxxxx;
>> >> >> ulf.hansson@xxxxxxxxxx; Zhangfei Gao
>> >> >> Cc: Haojian Zhuang; Chao Xie; Philip Rakity; Kevin Liu; Jialing Fu
>> >> >> Subject: [PATCH v5 03/13] mmc: sdhci: use regulator min/max voltage
>> >> >> range according to spec
>> >> >>
>> >> >> From: Kevin Liu <kliu5@xxxxxxxxxxx>
>> >> >>
>> >> >> For regulator vmmc/vmmcq, use voltage range as below
>> >> >> 3.3v/3.0v: (2.7v, 3.6v)
>> >> >> 1.8v: (1.7v, 1.95v)
>> >> >> Original code use the specific value which may fail in regulator
>> >> >> driver if it does NOT support the specific voltage.
>> >> >>
>> >> >> Signed-off-by: Jialing Fu <jlfu@xxxxxxxxxxx>
>> >> >> Signed-off-by: Kevin Liu <kliu5@xxxxxxxxxxx>
>> >> >
>> >> >
>> >> > Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>> >> >
>> >> > This patch restores sdhci devices to working state on Samsung boards
>> >> > (tested on GONI and UniversalC210) after merging "regulator: fix
>> >> > voltage
>> >> > check in regulator_is_supported_voltage()" patch to v3.7-rc6 (commit
>> >> > f0f98b19e23d4426ca185e3d4ca80e6aff5ef51b). Would be great to have it
>> >> > merged before the final v3.7 is out.
>> >> >
>> >> Marek,
>> >>
>> >> thanks a lot for the verification!
>> >> And your patch "mmc: sdhci: apply voltage range check only for
>> >> non-fixed regulators" (commit
>> >> d5b5205f2d480a47863dda0772d2d9dc47c2b51b, which has been merged in
>> >> mmc-next) can be reverted if this patch merged?
>> >
>> >
>> > Yes, it can be replaced with it, although there is still an issue that
>> > need
>> > to be resolved somehow. Right now SDHCI driver fails to initialize if
>> > support
>> > for dummy regulator is enabled.
>> >
>> Then I think the dummy issue can be resolved with your patch merged
>> and if you can just update your patch from
>> "regulator_count_voltages(host->vmmc) > 1"
>> to
>> "regulator_count_voltages(host->vmmc) > 0"
>> to let fix regulator work.
>
>
> regulator_count_voltages() returns 1 for both fixed regulators and for
> virtual dummy regulator, so the above change makes no sense.

I think regulator_count_voltage should return -EINVAL for dummy
regulator since n_voltages is not defined for dummy regulator:
int regulator_count_voltages(struct regulator *regulator)
{
struct regulator_dev *rdev = regulator->rdev;

return rdev->desc->n_voltages ? : -EINVAL;
}
can you double check this?

Err, right. I looked at the wrong SDHCI device :/ I have 3 of them on my
board - one with fixed regulator, one with 'real' and one without (with
virtual dummy regulator). I've applied my earlier patch and noticed that
it cured sdhci driver with dummy regulator, so I concluded that it did
the right job. Sorry for the confusion.

> However I was so focused on fixing the 2.8V supply case that I missed the
> fact that my "mmc: sdhci: apply voltage range check only for non-fixed
> regulators" patch also fixed the dummy regulator case.
>
> The conclusion is that applying both patches should finally fix the
> regulator issues with for the Samsung boards (2.8V supply for eMMC) and
> 'dummy-regulators' cases.
>

After thinking again, I think we don't need the check for
regulator_count_voltages.
In fact, dummy regulator should NOT be used for the sd/mmc power
supply. We should use controllable or fixed regulator. If dummy
regulator is used, then it means we won't control it and we don't know
its voltage. It's not reasonable for sd/mmc power supply. If dummy
regulator is used, I think it's ok to return error and disable all
voltage support caps.

The problem with dummy regulator is the fact that it can be enabled only
globally for all devices in the system. I think that the best solution
would be to introduce regulator_can_change_voltage() as Mark suggested.
I will post patches soon.

Best regards
--
Marek Szyprowski
Samsung Poland R&D Center


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