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

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Date:	Thu, 11 Jun 2009 17:28:50 -0400
From:	Andres Salomon <dilinger@...labora.co.uk>
To:	Tobias_Mueller@...m.info
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

On Thu, 11 Jun 2009 22:11:58 +0200
Tobias Müller <Tobias_Mueller@...m.info> wrote:

> >>  #define DRV_NAME "cs5535-gpio"
> >>  #define GPIO_BAR 1
> >> +#define GPIO_DEFAULT_MASK 0x0B003C66
> >
> > Where does this mask of available GPIOs originate from?
> 
> I had a comment in my original patch:
> 
> /**
> * 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).


> >> +     /* 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..


> 
> >> -             .ngpio = 28,
> >> +             .ngpio = 32,
> >
> > Since GPIOs 29-31 aren't externally available, and 28 is
> > unavailable anyways, shouldn't we just set ngpio to 28?
> I thought that 32 is in consistency with the datasheet as it always
> talks about 32 GPIO pins.

Fair enough.
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