linux-kernel - Re: [PATCH 1/2] mmc: core: allow a reset gpio to be configured.

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Date:	Fri, 28 Nov 2014 12:56:33 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	NeilBrown <neilb@...e.de>
Cc:	Chris Ball <chris@...ntf.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	GTA04 owners <gta04-owner@...delico.com>,
	Doug Anderson <dianders@...omium.org>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH 1/2] mmc: core: allow a reset gpio to be configured.

On 8 November 2014 at 01:14, NeilBrown <neilb@...e.de> wrote:
> If the regulator supplying an SDIO device is shared
> with another device, the turning the regulator 'on' and 'off'
> will not actually cycle power and so will not reset
> the device.
>
> This is particularly a problem for some wi2si wireless modules which
> have a BT module on chip and can share power lines.
> Without the power-cycle, subsequent reset commands fail.
>
> So allow a 'reset' gpio to be specified.  If provided, the
> line is asserted during power-up.

There have been several attempts to fix similar issues as this patch
does. The latest one I posted a few month ago, which wasn't accepted.
http://comments.gmane.org/gmane.linux.power-management.general/46635

There has also been some off-list discussions on especially how we
should describe this in DT and there were actually some consensus made
around that. Still I haven't seen any patches on the mailing lists.

So to summarize, I am really concerned that we keep having these power
sequence issues for SDIO devices and right now the discussion has been
on hold. I am considering to hack on it myself, since I am tired of
waiting. :-)

Regarding this patch, I don't intent to apply it.

Kind regards
Uffe
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