linux-kernel - Re: [PATCH] mmc/sdio: don't allow interface to runtime-suspend until probe is finished.

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Date:	Mon, 5 Dec 2011 21:37:07 +0200
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	NeilBrown <neilb@...e.de>
Cc:	linux-mmc@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	Daniel Drake <dsd@...top.org>,
	Joe Woodward <jw@...rafix.co.uk>, Chris Ball <cjb@...top.org>,
	Bing Zhao <bzhao@...vell.com>
Subject: Re: [PATCH] mmc/sdio: don't allow interface to runtime-suspend until
 probe is finished.

On Mon, Dec 5, 2011 at 9:06 PM, NeilBrown <neilb@...e.de> wrote:
> Challenge accepted.

cool :)

> Even if I don't find a better solution, this seems backwards.  Sure the
> default should be that PM is enabled, but individual board can request no
> PM on MMC interfaces where it is a problem.

I somewhat tend to pick a white listing approach, so we don't keep on
inflicting further pain on random sdio users (at least until we learn
more about the issues at hand), but I wouldn't object black listing.

> The chip has a requirement that the reset line is held down during power-on,
> and raised shortly after (I don't know exactly how short).  So if you just
> remove power and give it back, the chip doesn't come up properly.

Well, not according to Bing Zhao from Marvell:

http://www.mail-archive.com/linux-mmc@vger.kernel.org/msg08257.html

Though I agree that if we do find this reset line helping (and get it
to work cleanly with the help of some regulator code), the solution
might be much more robust.

> "It *should be* perfectly fine ..." :-)

heh, yeah :)

> We just have to make sure the bug powers up the card properly.
> Maybe I need to create a virtual regulator that powers on the real regulator,
> then raises the reset line.  I wonder how hard that is.

Btw did you try toggling the reset line manually and see if it really helps ?

> I'll spend some more time on this and get back to you - probably next week.

Very cool, thanks a lot.

Ohad.
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