linux-kernel - Re: [PATCH v2] mmc: core: Allow specifying current consumption

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Date:	Sat, 17 Oct 2015 10:09:38 -0700
From:	Bjorn Andersson <bjorn.andersson@...ymobile.com>
To:	Ulf Hansson <ulf.hansson@...aro.org>
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mmc <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH v2] mmc: core: Allow specifying current consumption

On Fri 16 Oct 05:55 PDT 2015, Ulf Hansson wrote:

> On 13 October 2015 at 03:00, Bjorn Andersson
> <bjorn.andersson@...ymobile.com> wrote:
> > This allows us to specify expected current consumption of the vmmc and
> > vqmmc regulators. This is needed to bring the supplying regulators out
> > of their low-power-mode while accessing the mmc.
> 
> This indeed makes sense, still I need to think a bit more on this.
> 

Thanks.

We can currently work around this by using "regulator-system-load" on
the vmmc regulator, but a proper fix would be nice.

> For example, can we allow these regulators to enter low power again at
> some times? If so, when and what should that current value be.
> 

The regulator framework recalculates the total load on a regulator upon
enable/disable, but currently it doesn't depend on the state of the
regulator.

I talked to Mark about this a while back and he was positive to us
correcting this, so disabled regulators wouldn't count towards the total
load of a regulator. (So that still is on my todo)

The second option would be to do what is done in the Qualcomm codeaurora
kernels, where the regulators are never disabled and there's a smaller
current specified for the suspend case.

This would require bigger changes to the mmc core I presume, but the
naming of the dt properties support such future adaption.

> Moreover, wouldn't vmmc|vqmmc-active-current be depending what eMMC/SD
> card that is attached?
> 

I would say so, I do however not know how to acquire or encode that
information. Any suggestions here are welcome.

Regards,
Bjorn
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