linux-kernel - Re: [PATCH] regulator: fixed: support deferred probe for DT GPIOs

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Date:	Fri, 29 Jun 2012 09:30:51 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	Liam Girdwood <lrg@...com>, linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCH] regulator: fixed: support deferred probe for DT GPIOs

On 06/28/2012 07:25 PM, Mark Brown wrote:
> On Thu, Jun 28, 2012 at 04:31:32PM -0600, Stephen Warren wrote:
> 
>> static struct fixed_voltage_config * 
>> -of_get_fixed_voltage_config(struct device *dev) 
>> +of_get_fixed_voltage_config(struct device *dev, bool
>> *defer_probe)
> 
> This is pretty contorted, we should just be able to pass the
> return value back more directly and of course ideally gpiolib would
> be doing the -EPROBE_DEFER for us anyway (I did send a patch for
> this, Grant didn't apply it due to a mostly unrelated issue in the
> current probe deferral implementation).  Or just defer if we don't
> get a config passed back or something.

I did consider making of_get_fixed_voltage_config() return a result
code, but then it needs some other way of returning the pointer, so
that seemed just as convoluted. Oh, I suppose it could use ERR_PTR()
to do that; that'd be nice and simple. Would that do?

Re: gpiolib doing it: How is that possible? of_get_named_gpio()
certainly can return -EPROBE_DEFER, but the caller would still need to
check it. The ideal case might be to just do:

ret = gpio_request(of_get_named_gpio(...));
if (ret)
    return ret;

and have gpio_request pass -EPROBE_DEFER from input to output.

i.e. only check the gpio_request() result code, not the
of_get_named_gpio() result code, and rely on gpio_request() to do
validation later.

But gpio_request takes an unsigned int, so the error code wouldn't
survive the translation:-(
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