linux-kernel - Re: [PATCH RFC] x86: Add user configurable GPIO-lib support

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Message-ID: <20080701110436.GA32365@elte.hu>
Date:	Tue, 1 Jul 2008 13:04:37 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Michael Buesch <mb@...sch.de>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	linux-kernel <linux-kernel@...r.kernel.org>,
	florian.fainelli@...ecomint.eu,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH RFC] x86: Add user configurable GPIO-lib support


* Michael Buesch <mb@...sch.de> wrote:

> So this adds user-configurable GPIO support through gpiolib on 
> subarchitectures that do not implement a GPIO implementation, yet. 
> Currently that's everything except X86_RDC321X.
> 
> The advantage of this is to make it possible to use generic PCI (or 
> other bus) GPIO extention cards in standard PCs through the standard 
> GPIO API.
> 
> If another subarch implements its own GPIO, it needs to add itself as 
> an inverted dependency to GPIO_USERSELECTION to make sure the user 
> does not enable two GPIO API implementations.
> 
> About the asm-x86/gpio.h:
> I'm not sure what this <gpio.h> include currently is.
> Can somebody explain that to me? Where is this supposed
> to include a gpio.h file from?
> 
> What's your opinion on this?

( i've Cc:-ed Florian on this who's maintaining the RDC R-321X bits. )

The longer-term goal is that we'd like to remove the explicit RDC 
sub-arch and just support such systems out of box on x86.

We are almost there - Florian already moved a few special drivers out of 
arch/x86, the only missing piece is this complication in 
include/asm-x86/timex.h:

 #ifdef CONFIG_X86_ELAN
 #  define PIT_TICK_RATE 1189200 /* AMD Elan has different frequency! */
 #elif defined(CONFIG_X86_RDC321X)
 #  define PIT_TICK_RATE 1041667 /* Underlying HZ for R8610 */
 #else
 #  define PIT_TICK_RATE 1193182 /* Underlying HZ */
 #endif

... once that is made dynamic/quirkable we are there.

And we could even remove the AMD Elan subarch that way: AFAICS it's a 
486 compatible with an A20 quirk and this PIT_TICK quirk.

... and if we do that we'll also remove these:

        select GENERIC_GPIO
        select LEDS_CLASS
        select LEDS_GPIO
        select NEW_LEDS

... and thus perhaps your GPIO_USERSELECTION patch should move into 
drivers/ and be generally accessible, not special to x86?

	Ingo
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