linux-kernel - Re: [PATCH 3/3 v2] at91/atmel-mci: inclusion of sd/mmc driver in at91sam9g45 chip and board

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Date:	Tue, 03 Nov 2009 15:30:56 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
CC:	Ben Nizette <bn@...sdigital.com>,
	Andrew Victor <avictor.za@...il.com>,
	linux-arm-kernel@...ts.infradead.org, linux-mmc@...r.kernel.org,
	"\"Thiago A.\" Corrêa" 
	<thiago.correa@...il.com>, kernel@...32linux.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	David Brownell <david-b@...bell.net>,
	David Brownell <dbrownell@...rs.sourceforge.net>
Subject: Re: [PATCH 3/3 v2] at91/atmel-mci: inclusion of sd/mmc driver in
 at91sam9g45 chip and board

Nicolas Ferre wrote:
> Ben Nizette :
>   
>> On Wed, 2009-10-28 at 21:53 +0200, Andrew Victor wrote:
>>     
>>> hi,
>>>
>>>       
>>>> Then I think it would be best to use GPIO_PIN_NONE. Makes it clear
>>>> what is expected and avoids confusion on what should be the proper
>>>> value.
>>>> I hope I'm not saying non-sense, but even if I am, I guess you can see
>>>> that I'm advocating against the magic numbers :)
>>>>         
>>> What magic numbers ?
>>>       
>> I think Thiago was referring to the "-1" in the original patch as the
>> magic number.
>>
>> Leaving the field blank to be initialised to 0 is certainly the
>> cleanest, I agree, but it doesn't actually /work/.  On many archs 0 is a
>> valid gpio number; the gpio_is_valid check used throughout the kernel
>> (including atmel-mci.c) looks like
>>
>> static inline int gpio_is_valid(int number)
>> {
>> 	/* only some non-negative numbers are valid */
>> 	return ((unsigned)number) < ARCH_NR_GPIOS;
>> }
>>     
>
> I understand that the better way to solve this issue is to:
> - keep the AT91 way of specifying not connected pins (= 0)
> - code the gpio_is_valid() function for at91 that tests this way of
> handling not connected gpio
>   
It doesn't appear that the gpio_is_valid function can be overridden by a
platform specific version. However, as you point out, on AT91 it appears
broken since anything less than AT91_PIN_PA0 (32) is not a valid gpio.

IIRC, we can't mark static inline functions as weak, and we don't want
to turn gpio_is_valid into an actual function call. We could do some
preprocessor magic, but that gets a bit messy.

CC'ed David Brownell, who does most of the gpiolib stuff. Any ideas?

~Ryan

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