linux-kernel - Re: [PATCH] mmc: dw_mmc: Change signal voltage error to dev

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Date:	Wed, 15 Oct 2014 01:34:00 +0530
From:	Alim Akhtar <alim.akhtar@...il.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Addy Ke <addy.ke@...k-chips.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Chris Ball <chris@...ntf.net>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: dw_mmc: Change signal voltage error to dev_dbg()

Hi Doug,

On Tue, Oct 14, 2014 at 9:57 PM, Doug Anderson <dianders@...omium.org> wrote:
> Alim,
>
> On Tue, Oct 14, 2014 at 5:02 AM, Alim Akhtar <alim.akhtar@...il.com> wrote:
>>> --- a/drivers/mmc/host/dw_mmc.c
>>> +++ b/drivers/mmc/host/dw_mmc.c
>>> @@ -1075,7 +1075,7 @@ static int dw_mci_switch_voltage(struct mmc_host *mmc, struct mmc_ios *ios)
>>>                 ret = regulator_set_voltage(mmc->supply.vqmmc, min_uv, max_uv);
>>>
>>>                 if (ret) {
>>> -                       dev_err(&mmc->class_dev,
>>> +                       dev_dbg(&mmc->class_dev,
>>>                                          "Regulator set error %d: %d - %d\n",
>>>                                          ret, min_uv, max_uv);
>>>                         return ret;
>> Well, I am ok with this but this info is very useful, what if PMIC
>> failed to actually set the voltage? may be because of some PMIC driver
>> bug or i2c driver bug? Ofcourse this can be found by turning MMC_DEBUG
>> ON, but is that worth in this case. Or is there a way to print that,
>> this failure is because of a regulator re-try?
>> your thoughts?
>
> I think that the regulator framework and the i2c framework are
> supposed to be reliable.  If they aren't reliable there will be lots
> of places that will have problems.  I think that you _could_:
>
> * In your regulator driver print an error when an i2c transfer fails.
>
> * In your regulator driver print an error if some unexpected event
> happens (like a regulator reports that the voltage didn't actually
> change).
>
> That would get you want you want, right?  ...but an error here doesn't
> belong and that's pretty much determined by (28f92b5 mmc: core: Try
> other signal levels during power up).  That patch wants to be able to
> try several different voltage levels and if we print an error in that
> case then it's going to be very confusing to the user.
>
Hmm...Ok, convincing enough to me, so
Reviewed-by: Alim Akhtar <alim.akhtar@...sung.com>
> -Doug



-- 
Regards,
Alim
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