linux-kernel - Re: [PATCH v2 2/3] mmc: dw_mmc: Use mmc_regulator_set_vqmmc in start_signal_voltage

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Date:	Mon, 15 Dec 2014 16:09:05 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Andrew Bresticker <abrestic@...omium.org>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Mark Brown <broonie@...nel.org>,
	Alexandru Stan <amstan@...omium.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	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 v2 2/3] mmc: dw_mmc: Use mmc_regulator_set_vqmmc in start_signal_voltage_switch

Andrew,

On Mon, Dec 15, 2014 at 3:44 PM, Andrew Bresticker
<abrestic@...omium.org> wrote:
>> -       if (!IS_ERR(mmc->supply.vqmmc)) {
>> -               ret = regulator_set_voltage(mmc->supply.vqmmc, min_uv, max_uv);
>> -
>> -               if (ret) {
>> -                       dev_dbg(&mmc->class_dev,
>> -                                        "Regulator set error %d: %d - %d\n",
>> -                                        ret, min_uv, max_uv);
>> -                       return ret;
>> -               }
>> -       }
>> +       mmc_regulator_set_vqmmc(mmc, ios);
>
> Shouldn't we check the return value here and bail out of the voltage
> switch procedure if it fails?

My thought was to purposely _not_ check the return value.  The comment
right above this says:

* Program the voltage.  Note that some instances of dw_mmc may use
* the UHS_REG for this.  For other instances (like exynos) the UHS_REG
* does no harm but you need to set the regulator directly.  Try both.

...I'm not 100% sure that I understand how the UHS_REG is supposed to
be implemented since I've never seen a system that uses it.  I was
assuming that if you have UHS_REG you don't need the regulator...

...but probably a better solution is to return the error if "
!IS_ERR(mmc->supply.vqmmc)".  Let me fix that up and repost.


-Doug
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