linux-kernel - Re: [PATCH v4 2/4] mmc: core: Add mmc_regulator_set

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Date:	Wed, 18 Mar 2015 21:09:33 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Mark Brown <broonie@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Alexandru Stan <amstan@...omium.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Addy Ke <addy.ke@...k-chips.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	"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>,
	Johan Rudholm <johan.rudholm@...s.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Tim Kryger <tim.kryger@...il.com>,
	Andrew Gabbasov <andrew_gabbasov@...tor.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/4] mmc: core: Add mmc_regulator_set_vqmmc()

Ulf,

On Tue, Mar 17, 2015 at 3:23 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> This will get us within .3V of whatever vmmc is.  If vmmc is 3.3V, it
>> will allow vqmmc of 3.0V - 3.6V.
>>
>> This _seems_ sane to me and given any sane system design we should be
>> fine here, I think.  I can't see someone designing a system where
>> vqmmc was not within .3V of vmmc, can you?  If we think someone will
>> actually build a system where vmmc is 3.3V and vqmmc can't go higher
>> than 2.7V then we'll either need to increase the tolerance here or add
>> a new asymmetric system call like my original patches did.
>
> I know about SoC that supports 3.4V vmmc and 2.9V vqmmc.
>
> What I think we need is the option to have a policy here. We need to
> allow voltage levels stated by the spec and at the same time try chose
> the one best suited. That's not being accomplished here.
>
> Moreover, I wonder whether it's okay (from spec perspective) to have
> vqmmc at a higher voltage level than vmmc. I don't think that's
> allowed, but I might be wrong.

OK, so sounds like I need to add a regulator_set_voltage_tol2()
function that takes in an upper tolerance and a lower.  We can use the
same rough implementation in the core we have today (if Mark is OK
with that) with regulator_set_voltage_tol() but just allow it to be
asymmetric.

>From what I see in the spec for 3.3V cards are supposed to react to a
high signal that is .625 * VDD - VDD + .3


I might not be able to get to this till next week, though...

-Doug
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