linux-kernel - Re: [PATCH] gpio: of_get_named_gpio_flags() return -EPROBE

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Date:	Mon, 18 Jun 2012 11:19:15 +0200
From:	Roland Stigge <stigge@...com.de>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	cjb@...top.org, grant.likely@...retlab.ca, rob.herring@...xeda.com,
	rmk+kernel@....linux.org.uk, ulf.hansson@...ricsson.com,
	linus.walleij@...aro.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org, aletes.xgr@...il.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] gpio: of_get_named_gpio_flags() return -EPROBE_DEFER
 if GPIO not yet available

On 06/18/2012 04:06 AM, Stephen Warren wrote:
> On 06/17/2012 04:11 AM, Roland Stigge wrote:
>> of_get_named_gpio_flags() and of_get_named_gpio() return -EPROBE_DEFER if the
>> respective GPIO is not (yet) available. This is useful if driver's probe()
>> functions try to get a GPIO whose controller isn't probed yet. Thus, the driver
>> can be probed again later on.
>>
>> The function still returns -EINVAL on other errors (parse error or node doesn't
>> exist). This way, the case of an optional/intentionally missing GPIO is handled
>> appropriately.
> 
> While I agree this is a correct change, it is going to break some
> existing code - at least sound/soc/tegra/tegra_{wm8903.c,alc5632.c}.

Can you please tell in which way the patch breaks those drivers?
However, I can see that those drivers solved the same problem in a
different way (deferring of_get_named_gpio(), via the sound init()). So
they could be adjusted to take advantage of new -EPROBE_DEFER.

> I'm
> happy to send patches for those files though (is this going into 3.5 or
> 3.6?).

For 3.6 would be best, IMO.

> However, have you audited all existing callers (including
> indirect, e.g. through plain of_get_named_gpio()) for issues this will
> cause?

Thanks for the hint, I searched the code and found

drivers/spi/spi-pl022.c

to be using -ENODEV as indication to return -EPROBE_DEFER from probe().
Will send a patch that adjusts to our of_get_named_gpio_flags() patch
and if it's good, we should join the two.

Some drivers possibly suffer from the same issue that the patch adresses:

drivers/mfd/twl6040-core.c
drivers/staging/nvec/nvec.c
drivers/usb/host/ohci-at91.c
drivers/usb/host/ehci-tegra.c
drivers/usb/gadget/at91_udc.c
drivers/spi/spi-imx.c
drivers/spi/spi-sirf.c
drivers/mmc/host/sdhci-tegra.c
drivers/mmc/host/omap_hsmmc.c
drivers/mmc/host/mxs-mmc.c
drivers/mmc/host/sdhci-esdhc-imx.c
drivers/regulator/tps62360-regulator.c
drivers/regulator/fixed.c

But the breakage therefore exists even before the patch.

Other drivers don't handle the result of of_get_named_gpio*() correctly
at all:

drivers/power/sbs-battery.c

I can help the respective maintainers to work out this issue when we
have the EPROBE_DEFER ready in gpiolib-of.c.

Thanks,

Roland
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