linux-kernel - Re: [PATCH V3 1/5] i2c: Add irq_gpio field to struct i2c_client, i2c_board

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Message-ID: <20110920041629.GC30517@ponder.secretlab.ca>
Date:	Mon, 19 Sep 2011 22:16:29 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Stephen Warren <swarren@...dia.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Ben Dooks <ben-linux@...ff.org>,
	Jonathan Cameron <jic23@....ac.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Russell King <linux@....linux.org.uk>,
	Andrew Chew <achew@...dia.com>, linux-iio@...r.kernel.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-i2c@...r.kernel.org,
	spi-devel-general@...ts.sourceforge.net
Subject: Re: [PATCH V3 1/5] i2c: Add irq_gpio field to struct i2c_client,
 i2c_board_info.

On Fri, Sep 02, 2011 at 08:56:20AM +0200, Jean Delvare wrote:
> Stephen,
> 
> Can you please fix your e-mail client / system / whatever so that your
> patch series are no longer sent duplicated?
> 
> On Thu,  1 Sep 2011 16:04:27 -0600, Stephen Warren wrote:
> > Some devices use a single pin as both an IRQ and a GPIO. In that case,
> > irq_gpio is the GPIO ID for that pin. Not all drivers use this feature.
> > Where they do, and the use of this feature is optional, and the system
> > wishes to disable this feature, this field must be explicitly set to a
> > defined invalid GPIO ID, such as -1.
> > 
> > Signed-off-by: Stephen Warren <swarren@...dia.com>
> > ---
> > v3: Also add the field to i2c_board_info, and copy the field from
> >     i2c_board_info to i2c_client upon instantiation
> 
> I don't get the idea. The i2c core doesn't make any use of the field,
> and that field will only be used by a few drivers amongst the 420+
> i2c drivers in the tree. This looks like a waste of memory. What's wrong
> with including the new field in the private platform or arch data
> structure for drivers which need it?

I have to second the concern; but for a different reason.  This
shouldn't even remotely be necessary.  If the pin is used as an
interrupt, then interrupt controller driver (which I would assume is
also the gpio controller driver) should be responsible for setting up
the pin so that it can be used correctly as a irq line.  Why does the
gpio number need to be explicitly passed?

g.

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