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

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Message-ID: <74CDBE0F657A3D45AFBB94109FB122FF04B327A2A4@HQMAIL01.nvidia.com>
Date:	Thu, 1 Sep 2011 08:36:53 -0700
From:	Stephen Warren <swarren@...dia.com>
To:	Arnd Bergmann <arnd@...db.de>, Jonathan Cameron <jic23@....ac.uk>
CC:	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()

Arnd Bergmann wrote at Thursday, September 01, 2011 5:07 AM:
> On Thursday 01 September 2011, Jonathan Cameron wrote:
> > On 08/31/11 20:45, Andrew Chew wrote:
> > >> Subject: [PATCH 1/3] staging:iio:magnetometer:ak8975 Don't
> > >> use irq_to_gpio()
> > >>
> > >> Tegra doesn't have irq_to_gpio() any more, and ak8975 is included in
> > >> tegra_defconfig. This causes a build failure. Solve this with
> > >> a heavy-handed
> > >> method for now.
> > >>
> > >> I suspect the long-term solution is to pass both the IRQ and GPIO IDs
> > >> to the driver; the GPIO ID coming from either platform data,
> > >> or perhaps
> > >> enhancing struct i2c_client to add a gpio field alongside irq.
> > >>
> > >> Signed-off-by: Stephen Warren <swarren@...dia.com>
> > >> ---
> > >
> > > The three patches in this set LGTM.
> > >
> > > Acked-by: Andrew Chew <achew@...dia.com>
> > >
> >
> > Hmm.. I'd like to see some means of passing that in. Perhaps as simple as passing
> > a pointer to an int in as platform_data.  Patch to follow.
> 
> My feeling is that we should just add another field to
> struct i2c_client. There are probably more drivers that
> need the same thing, making it appropriate to increase
> the size of that struct for everything device instead of
> adding platform_data to a subset of the devices.

That sounds reasonable to me.

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?

-- 
nvpublic

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