linux-kernel - Re: [PATCH 1/3] staging:iio:magnetometer:ak8975 Don't use irq_to

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Date:	Thu, 1 Sep 2011 18:20:25 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Jonathan Cameron <jic23@....ac.uk>, Andrew Chew <AChew@...dia.com>,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	Russell King <linux@....linux.org.uk>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 1/3] staging:iio:magnetometer:ak8975 Don't use irq_to_gpio()

On Thursday 01 September 2011, Stephen Warren wrote:
> One question: When we add this field, how do drivers tell whether a value
> of 0 is an uninitialized field, or a legitimate GPIO value of 0? Should we
> add a flag to indicate validity, or just work hard to not enable driver-
> side code to use this value until we've fixed up all places that instantiate
> the driver to initialize the field to some invalid value like -1?

I think it's enough to coordinate the driver with the initialization of the
i2c data. If a driver requires a GPIO number, it can assume that it's valid.
Drivers that don't need one don't care. If it's an optional feature, you
might want to either use platform_data after all, or use different identifiers
for devices that have a gpio vs. those that have none -- in effect those are
different types of devices handled by the same driver.

	Arnd
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