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

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Date:	Thu, 11 Jun 2009 23:35:55 +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

>> /**
>> * 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).

>> >> +     /* disable output aux 1 & 2 on this pin */
>> >> +     __cs5535_gpio_clear(chip, offset, GPIO_OUTPUT_AUX1);
>> >> +     __cs5535_gpio_clear(chip, offset, GPIO_OUTPUT_AUX2);
>> >> +
>> >> +     /* disable input aux 1 on this pin */
>> >> +     __cs5535_gpio_clear(chip, offset, GPIO_INPUT_AUX1);
>> >> +
>> >> +     /* disable output */
>> >> +     __cs5535_gpio_clear(chip, offset, GPIO_OUTPUT_ENABLE);
>> >> +
>> >> +     /* enable input */
>> >> +     __cs5535_gpio_set(chip, offset, GPIO_INPUT_ENABLE);
>> >
>> > I don't think this is the right place for all of this.  Your earlier
>> > email mentioned disabling OUT_AUX{1,2} for outputs, and IN_AUX for
>> > inputs.  I'm fine with doing that here, but I don't see why you're
>> > also disabling output and enabling input by default.
>>
>> I mentioned this in an ealier mail too. When I request the GPIO from
>> userspace the direction file always contains "in", so I thought
>> this is the standard direction after resetting as I should be in a
>> defined state after requesting. But I didn't found anything
>> about this in GPIO lib documentation, so I would be fine to change
>> this if there is any common default behavoir.
>
> To be honest, I'd have to play around with it a bit before I
> knew whether it actually breaks anything or not. I'm not sure if
> it would break anything on OLPC, and I don't have any other geode
> machines that do anything interesting w/ GPIOs.
>
> Maybe David can clear up whether this behavior is correct from the
> userspace GPIO usage standpoint..
This would be nice. But I wouldn't have a problem when those
two statements are removed. I just thought it's better to put them
in a defined state.
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