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 22:23:17 +0100
From:	Philip Rakity <prakity@...dia.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
CC:	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>, Chris Ball <cjb@...top.org>
Subject: Re: [PATCH v2] mmc: sdhci: apply voltage range check only for
 non-fixed regulators


Hi Marek,

Is the regulator dedicated ?  or is it shared ?   Is it used for eMMC ?

If it cannot be turned off -- then just don't list it in the regulators list for vmmc.  

If it CAN be turned off then need to get back to you.

Philip 

On Nov 13, 2012, at 2:14 PM, Chris Ball <cjb@...top.org> wrote:

> 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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