linux-kernel - Re: [PATCH 3/8] mmc: core: Add mmc_regulator_set

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Date:	Thu, 10 Sep 2015 14:40:26 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Heiko Stuebner <heiko@...ech.de>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"tgih.jun@...sung.com" <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	linux-mmc <linux-mmc@...r.kernel.org>, linux-clk@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/8] mmc: core: Add mmc_regulator_set_vqmmc()

On 2 September 2015 at 18:20, Doug Anderson <dianders@...omium.org> wrote:
> Ulf,
>
> On Wed, Sep 2, 2015 at 4:38 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>> +/**
>>> + * mmc_regulator_set_vqmmc - Set VQMMC as per the ios
>>> + *
>>> + * For 3.3V signaling, we try to match VQMMC to VMMC as closely as possible.
>>
>> Looking at the code, I don't think this statement is entirely true.
>> Isn't it so that we will be trying with a maximum tolerance of 0.3 V
>> towards the VMMC voltage level (then fall-back to the complete range)?
>> Perhaps you can find a better way to describe that in the change log.
>
> If regulator_set_voltage_triplet() is ever implemented more correctly
> then the description here is correct.  ...the problem is that
> regulator_set_voltage_triplet() is still using the same shortcut that
> regulator_set_voltage_tol() was using.

Okay, let's mention that somehow.

>
>
>>> +int mmc_regulator_set_vqmmc(struct mmc_host *mmc, struct mmc_ios *ios)
>>> +{
>>> +       int volt, min_uV, max_uV;
>>> +
>>> +       /* If no vqmmc supply then we can't change the voltage */
>>> +       if (IS_ERR(mmc->supply.vqmmc))
>>> +               return -EINVAL;
>>
>> In general vqmmc is considered as an optional regulator and that's
>> also how host drivers treat it. So perhaps it would make sense to
>> return 0 here instead of an error code or what do you think?
>
> The idea is that since this is intended to be called by
> start_signal_voltage_switch() and having no vqmmc should be considered
> an error for start_signal_voltage_switch() then it should be an error
> here.  What do you think?

Okay!

>
>
>>> +
>>> +               /* try to stay close to vmmc at first */
>>> +               if (!mmc_regulator_set_voltage_if_supported(mmc->supply.vqmmc,
>>> +                                               min_uV, volt, max_uV))
>>> +                       return 0;
>>> +
>>> +               return mmc_regulator_set_voltage_if_supported(mmc->supply.vqmmc,
>>> +                                               2700000, volt, 3600000);
>
> The whole fact that there are two calls here is really just because of
> the limitations of the current implementation of
> regulator_set_voltage_triplet().  If that implementation is ever fixed
> then we'd just need a single call.  Probably worth a comment saying
> that?

Yes, please!

Kind regards
Uffe
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