Mark Brown wrote at Thursday, August 04, 2011 11:35 PM:

On Thu, Aug 04, 2011 at 08:53:34PM -0700, Stephen Warren wrote:

quoted

Well, things break. This is essentially the problem I was describing in
the PATCH 0 email, just with a slightly different motivation.

There's a bunch of existing code using that idiom.

Certainly.

quoted

I suppose that an alternative here would be to simply ignore any errors
from gpio_request. This might have the benefit of removing the need for
the other two patches I posted in the series. However, it seems a little
dirty; one benefit of the IRQ code calling gpio_request and honoring
errors would be to detect when some completely unrelated code had a bug
and had called gpio_request on the GPIO before. Such detection would be
non-existent if we don't error out on gpio_request. Perhaps some mechanism
is needed to indicate that the driver has explicitly already called
gpio_request for a legitimate shared purpose, and only then ignore
errors?

But it's not a bug to use a GPIO as an IRQ source, otherwise we wouldn't
have gpio_to_irq() in the first place.

True, but I think there are two cases:

1) Some code legitimately uses a pin as both a GPIO and IRQ, and is fully
cognizant of the fact, just like in your example -> no bug.

2) Two pieces of unrelated code somehow accidentally get a GPIO and IRQ
number that map to the same resource, e.g. due to incorrect board files or
Device Tree content. This is probably a bug, but ends up looking exactly
the same as far as the IRQ code's gpio_request call failing in the patch I
posted.

Feels like we need a backchannel
between gpiolib and the IRQ code to do this.  Or perhaps the drivers
that implement this should be taking care of setting up the GPIO mode?

-- 
nvpublic