linux-kernel - Re: [patch/rfc 2.6.19-rc5] arch-neutral GPIO calls

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Message-ID: <4558DC75.6040109@billgatliff.com>
Date:	Mon, 13 Nov 2006 14:58:29 -0600
From:	Bill Gatliff <bgat@...lgatliff.com>
To:	David Brownell <david-b@...bell.net>
CC:	Paul Mundt <lethal@...ux-sh.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Andrew Victor <andrew@...people.com>,
	Haavard Skinnemoen <hskinnemoen@...el.com>, jamey.hicks@...com,
	Kevin Hilman <khilman@...sta.com>,
	Nicolas Pitre <nico@....org>,
	Russell King <rmk@....linux.org.uk>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [patch/rfc 2.6.19-rc5] arch-neutral GPIO calls

David Brownell wrote:

>On Monday 13 November 2006 12:26 pm, Bill Gatliff wrote:
>
>  
>
>>>Nah; look at arch/arm/plat-omap/gpio.c and ignore the mess, but observe
>>>that what you see there is essentially a bunch of "gpio controller"
>>>classes using the ugly "switch(type)" dispatch scheme instead of the
>>>prettier "type->op()" dispatch scheme.  All that stuff needs to be
>>>cleaner, but for now it'd suffice to add a new FPGA typecode.
>>>      
>>>
>>Agreed.  But if we add to the machine descriptor, then not only do you 
>>not need to touch arch-omap/gpio.c, but you can take that switch 
>>statement out, too.  Just one less chunk of code to tweak when a new 
>>platform is supported.
>>    
>>
>
>Do non-ARM platforms have board/machine descriptors on Linux, though?
>I thought most didn't ...
>  
>


PPC does.  See arch/ppc/platforms/chestnut.c:platform_init().

>One could come up with an implementation that uses GPIO numbers
>as indices into a descriptor array, and using board-specific
>initialization of that array ... just like with IRQs and irq_chip.
>
>That could lead to heavier weight implementations than I'd prefer
>to see (since GPIOs are a very light weight notion!), but it'd
>certainly provide a more reusable way to add GPIO controllers.
>
>All behind the API I proposed, note -- no changes needed.
>  
>


Indeed.  I'm all for lightweight, but especially for nice and neat code.


b.g.

-- 
Bill Gatliff
bgat@...lgatliff.com

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