linux-kernel - Re: [PATCH] mmc: mmci.c: Defer probe() in case of missing GPIOs

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Date:	Sat, 16 Jun 2012 16:57:48 +0200
From:	Roland Stigge <stigge@...com.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	cjb@...top.org, grant.likely@...retlab.ca, rob.herring@...xeda.com,
	ulf.hansson@...ricsson.com, linus.walleij@...aro.org,
	sebastian.rasmussen@...ricsson.com, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org, aletes.xgr@...il.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] mmc: mmci.c: Defer probe() in case of missing GPIOs

On 16/06/12 16:26, Russell King - ARM Linux wrote:
> On Sat, Jun 16, 2012 at 04:14:59PM +0200, Roland Stigge wrote:
>> If the GPIOs used by the MMCI driver are not registered yet when the
>> driver is probe()d, they can't be used. This happens if the mmci driver
>> is probed before the respective GPIO controller (e.g. on the LPC32xx
>> EA3250 board, the PCA9532 GPIO controller would be initialized via DT
>> after mmci). Therefore, we defer mmci in this case.
> 
> This code is wrong.  There are platforms where plat->gpio_cd is negative
> (because there isn't an associated GPIO) and we still expect the driver
> to successfully bind.  In that case, the driver gets the CD and WP
> information via the status callback.
> 
> So this is an incompatible change with existing (and required) driver
> behaviour.

As someone just told me, in the case of no GPIO, we would have gpio_cd
== -ENODEV. Would it be sufficient to check for -ENODEV (in which case
we would do without GPIO), and otherwise return -EPROBE_DEFER?

Or is it necessary to flag DT-bound GPIOs somehow additionally to handle
this new case?

Thanks in advance,

Roland
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