linux-kernel - Re: [PATCH v2] pinctrl: bcm2835: Start GPIO numeration at zero

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Message-ID: <54503F9D.7080808@wwwdotorg.org>
Date:	Tue, 28 Oct 2014 19:15:09 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Matthias Klein <matthias.klein@...ux.com>,
	linux-rpi-kernel@...ts.infradead.org, linus.walleij@...aro.org
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] pinctrl: bcm2835: Start GPIO numeration at zero

On 10/28/2014 01:03 AM, Matthias Klein wrote:
> 
> Am 28.10.2014 um 01:00 schrieb Stephen Warren:
>> On 10/27/2014 05:05 PM, Matthias Klein wrote:
>>
>>> - To be in sync with the GPIO numbers in the datasheet / documentation
>>
>> I assume that's only relevant because of the second point; the GPIO
>> IDs in DT files already match the datasheet.
>>
>>> - For userland applications which rely on these GPIO numbers
>>
>> This isn't a scalable solution for that; this "fix" can only work for
>> a single GPIO controller in any one system. It'd be better for all
>> usage to search for the correct GPIO controller in sysfs, find the
>> base address of that, and then add on the controller-relative GPIO ID.
>> That way, the same approach is taken irrespective of which GPIO
>> controller is in use, and there are no special cases.
>>
>> Perhaps this could be simplified (removing the need to adding
>> base+offset to get the Linux ID) if the GPIO core exported a
>> per-controller directory in sysfs for GPIO manipulation (the files in
>> which used controller-relative numbering), rather than having a single
>> directory using Linux-internal global GPIO numbering; something like
>> /sys/class/gpio/gpio@...00000/export which uses ID 0..N vs.
>> /sys/class/gpio/export which uses IDs X..X+N where X is arbitary.
> 
> Would you accept a patch which implements the "gpio-base" property into
> the device tree for pinctrl-bcm2835?

DT is supposed to represent HW features, in an OS-agnostic way, and a
"GPIO base" is a Linux-specific SW concept.
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