Re: Any news on Runtime Interpreted Power Sequences

From: NeilBrown
Date: Mon Oct 28 2013 - 20:10:56 EST

On Mon, 28 Oct 2013 16:53:44 -0700 Mark Brown <broonie@xxxxxxxxxx> 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


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