linux-kernel - Re: [PATCH 1/2] cs5535-gpio: add AMD CS5535/CS5536 GPIO driver support

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Message-ID: <17be05570906200320t5be9393areaa39c7332d381bc@mail.gmail.com>
Date:	Sat, 20 Jun 2009 12:20:23 +0200
From:	Tobias Müller <Tobias_Mueller@...m.info>
To:	Andres Salomon <dilinger@...labora.co.uk>
Cc:	akpm@...ux-foundation.org, Randy Dunlap <randy.dunlap@...cle.com>,
	deepak@...top.org, Takashi Iwai <tiwai@...e.de>,
	linux-kernel@...r.kernel.org, linux-geode@...ts.infradead.org,
	jordan@...micpenguin.net, cjb@...top.org,
	David Brownell <david-b@...bell.net>
Subject: Re: [PATCH 1/2] cs5535-gpio: add AMD CS5535/CS5536 GPIO driver 
	support

2009/6/13 Andres Salomon <dilinger@...labora.co.uk>:
> On Thu, 11 Jun 2009 23:35:55 +0200
> Tobias Müller <Tobias_Mueller@...m.info> wrote:
>
>> >> /**
>> >> * Some GPIO pins
>> >> *  31-29,23 : reserved (always mask out)
>> >> *  28       : Power Button
>> >> *  26       : PME#
>> >> *  22-16    : LPC
>> >> *  14,15    : SMBus
>> >> *  9,8      : UART1
>> >> *  7        : PCI INTB
>> >> *  3,4      : UART2/DDC
>> >> *  2        : IDE_IRQ0
>> >> *  1        : AC_BEEP
>> >> *  0        : PCI INTA
>> >> *
>> >> * If a mask was not specified, be conservative and only allow:
>> >> *  1,2,5,6,10-13,24,25,27
>> >> */
>> >>
>> >> I'll add this in my patch to clear it out.
>> >>
>> >
>> > But why are you being conservative in the first place?  If
>> > something's using GPIOs, unless they're unmapped, you should allow
>> > it to use them without requiring a boot arg.
>> >
>> > For example, OLPC uses GPIO 7 for its DCON IRQ.  With the masking
>> > scheme, OLPC will need to set that mask from the default.  I don't
>> > see the point of having the mask at all if other drivers in the
>> > kernel are going to be requesting GPIOs (presumably they know what
>> > they're doing).
>> Hmm... OK, this makes sense. So default mask allow everything exept
>> reserved pins and pin 28 (power button).
>>
>> I think the mask is quite useful if you've critical things on GPIO
>> pins and they should be changeable (especially from userspace and when
>> non-root users are allowed to use userspace gpio).
>
> I agree that it would be useful for userspace, just not for
> kernelspace.  Is there a way that you can have it only enforce the
> mask if the request is coming from userspace?

I didn't find a way to find out if a request is coming from userspace, so at
the moment I think it's only possible to set it global.
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