linux-kernel - Re: [PATCH v2] leds: provide helper to register "leds-gpio" devices

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Message-ID: <1302097097.22904.41.camel@rex>
Date:	Wed, 06 Apr 2011 06:38:17 -0700
From:	Richard Purdie <rpurdie@...ys.net>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	H Hartley Sweeten <hartleys@...ionengravers.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Sascha Hauer <s.hauer@...gutronix.de>, kernel@...gutronix.de
Subject: Re: [PATCH v2] leds: provide helper to register "leds-gpio" devices

On Wed, 2011-04-06 at 14:33 +0200, Uwe Kleine-König wrote:
> On Wed, Apr 06, 2011 at 04:52:18AM -0700, Richard Purdie wrote:
> > I guess the motivation might be that if a given platform has many
> > different LED configurations, you're trying to remove the ones you don't
> > need from memory? Given all the above I'd suggest that this function
> > should really be added to the platform device code if anywhere and
> "platform device code" means e.g. arch/arm/plat-mxc or drivers/base
> here?

Yes.

> > doesn't belong in the LED subsystem as its not an LED specific problem.
> yeap, that's it. Note that this thread[1] started on the linux-arm-kernel
> mailing list with a imx-specific version of this function. With the
> background of Linus' recent rant against churn in arch/arm several
> people pointed out that this can better go to a more generic place where
> not only arm/imx, but also arm/omap and even powerpc can use the same
> code. So the (IMHO) obvious place to put the code is near the driver.
> 
> And yes, the problem is not LED specific, but a function that creates
> and registers a leds-gpio device *is* LED specific. A while back I
> thought about introducing something like drivers/register/*, but I'm
> sure this won't scale. Either you need a header per device type (or at
> subsystem) or a single header. Both look ugly in my eyes. Having the
> prototype in include/linux/leds.h seems the right thing, because
> platform code needs to include that anyhow to provide a struct
> gpio_led_platform_data.
> 
> I don't consider something wrong here, because the Linux device model
> requires that you have a driver and a device. Both have to match and the
> device (usually) is created at boot time. Because of the needed match
> it's natural to have device use (aka driver) and device creation at the
> same place. Because of the boot time thing the code needs to be
> built-in.

It should only be built-in on platforms that both use leds-gpio and want
to use this function at boot time. This is not the description of
leds-core.c.

I understand the issue and the desire to move it into common code, I
think that is good but I don't think you've found the most appropriate
place yet.

I'm tempted to suggest making the function a static inline in leds.h (or
create an leds-gpio.h and move the struct definition there too).

Cheers,

Richard
-- 
Linux Foundation
http://www.yoctoproject.org/

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