linux-kernel - Re: Any news on Runtime Interpreted Power Sequences

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Message-ID: <20131029111037.6e59499d@notabene.brown>
Date:	Tue, 29 Oct 2013 11:10:37 +1100
From:	NeilBrown <neilb@...e.de>
To:	Mark Brown <broonie@...nel.org>
Cc:	Alex Courbot <acourbot@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: Any news on Runtime Interpreted Power Sequences

On Mon, 28 Oct 2013 16:53:44 -0700 Mark Brown <broonie@...nel.org> wrote:

> On Mon, Oct 28, 2013 at 10:10:04PM +1100, NeilBrown wrote:
> 
> > I agree that this power-up sequence should be a property of the device.
> > However until the device has been powered up, Linux doesn't know about it.
> > Neither a board file or a devicetree can (as far as I can tell), tell the
> > MMC port that a particular card is attached.  Rather the host probes the card
> > to see what it is.
> > So there isn't any way for the device driver to get control at the
> > appropriate time to effect the proper sequencing.
> 
> If it is a genuinely pluggable MMC slot then I'd expect the sequence to
> be implementing whatever is required for standard MMC enumeration to
> work.  If the device is a soldered down one with extra control (as is
> quite common) then there shouldn't be a problem describing it?

Yes, the device is soldered down and has a reset line that needs to be pulsed
low at about the same time that the MMC port enables the regulator.

How do you propose that I describe this?  Which driver should know about the
reset GPIO, how to I tell it about the GPIO, and which function should do the
pulsing?

Thanks,
NeilBrown

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