linux-kernel - Re: [PATCH RESEND 4/6 v13] gpiolib: Fix default attributes for class

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Date:	Fri, 15 Feb 2013 22:55:14 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Roland Stigge <stigge@...com.de>, gregkh@...uxfoundation.org,
	linus.walleij@...aro.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, w.sang@...gutronix.de,
	jbe@...gutronix.de, plagnioj@...osoft.com, highguy@...il.com,
	broonie@...nsource.wolfsonmicro.com, daniel-gl@....net,
	rmallon@...il.com, sr@...x.de, wg@...ndegger.com,
	tru@...k-microwave.de, mark.rutland@....com
Cc:	Roland Stigge <stigge@...com.de>
Subject: Re: [PATCH RESEND 4/6 v13] gpiolib: Fix default attributes for class

On Tue, 15 Jan 2013 12:51:54 +0100, Roland Stigge <stigge@...com.de> wrote:
> There is a race condition between creating a gpio or gpiochip device and adding
> default attributes. This patch fixes this by defining the default attributes as
> dev_attrs of the class. For this, it was necessary to create a separate
> gpiochip_class besides gpio_class.
> 
> Signed-off-by: Roland Stigge <stigge@...com.de>

Hi Roland,

Yup, that's a bug. Thanks for looking at this. Unfortunately creating a
new class creates a new problem because it changes the userspace ABI
(the gpiochip simlinks move to a different class directory).

Instead, I think the correct solution here is to use (struct device *)->groups
to add attributes to a device. Unfortunately that means that
create_device() won't work anymore. It does some useful setup work
though that I don't want to have to reproduce. You could create a
variant that also allows groups to be set, or you could factor out the
allocation/setup stuff so we can do an allocate/fixup/register sequence.

g.

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