linux-kernel - Re: [PATCH 1/2] leds: Add generic support for memory mapped LEDs

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Date:	Mon, 26 Nov 2012 16:10:35 +0000
From:	Pawel Moll <pawel.moll@....com>
To:	Vasily Khoruzhick <anarsoul@...il.com>
Cc:	Bryan Wu <cooloney@...il.com>, Richard Purdie <rpurdie@...ys.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>
Subject: Re: [PATCH 1/2] leds: Add generic support for memory mapped LEDs

On Mon, 2012-11-26 at 15:37 +0000, Vasily Khoruzhick wrote:
> On Thu, Nov 1, 2012 at 8:58 PM, Pawel Moll <pawel.moll@....com> wrote:
> > LEDs are often controlled by writing to memory mapped
> > register. This patch adds:
> >
> > 1. Generic functions for platform code and drivers to create
> >    class device for LEDs controlled by arbitrary bit masks.
> >    The control register value is read, modified by logic AND
> >    and OR operations with respective mask and written back.
> >
> > 2. A platform driver for simple use case when one or more LED
> >    are controlled by consecutive bits in a register pointed
> >    at by the platform device's memory resource. It can be
> >    particularly useful for MFD cells being part of an other
> >    device.
>
> This MMIO controls some latch (or whatever) which is actually GPIO.
> So implementing generic GPIO MMIO driver and using leds-gpio on top of
> it appears to be a better solution for me.

I won't argue that it is doable - I don't even have to implement the
MMIO GPIO driver, because my MFD already has a set of pseudo-GPIO lines
and extending those won't be a problem at all an I'll do exactly that if
there is no other choice. But at the same time I hope you would agree
that my_code->gpio_controller->gpio_led_description->register_device
chain is longer than my_code->mmio_led one if you want to add a single
"status" led for your little board ;-). I don't event mention that at
least couple of the existing drivers follow the same "MMIO pattern"
blindly.

Nevertheless I'd really like to hear from the maintainers...

Thanks!

Paweł


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