linux-kernel - Re: FW: [PATCH v2] mmc: sdhci: apply voltage range check only for non-fixed regulators

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Date:	Wed, 14 Nov 2012 16:36:28 +0800
From:	Kevin Liu <keyuan.liu@...il.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	m.szyprowski@...sung.com, Chris Ball <cjb@...top.org>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	kyungmin.park@...sung.com, lrg@...com,
	Philip Rakity <prakity@...dia.com>
Subject: Re: FW: [PATCH v2] mmc: sdhci: apply voltage range check only for
 non-fixed regulators

2012/11/14 Mark Brown <broonie@...nsource.wolfsonmicro.com>:
> On Wed, Nov 14, 2012 at 03:11:37PM +0800, Kevin Liu wrote:
>
>> -             ret = regulator_set_voltage(host->vqmmc, 3300000, 3300000);
>> +             ret = regulator_set_voltage(host->vqmmc, 2700000, 3600000);
>
> Should this be regulator_set_voltage_tol()?  Otherwise it'd be good to
> explain where the numbers come from.
In SD physical layer spec 3.01 chapter 6.6.1, the threshold level for
voltage range is defined as below:
Vdd(min) = 2.7V while Vdd(max) = 3.6V.
The card should work within the voltage range.

If you are afraid the voltage value is too aggressive, maybe we can
use regulator_set_voltage_tol() to set a smaller range.
But which range should be reasonable?

>> +             ret = regulator_is_supported_voltage(host->vmmc, 1700000,
>> +                     1950000);
>
> We should really add a regulator_is_supported_voltage_tol...  let me
> just do that.
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