On Thu, Oct 18, 2012 at 6:38 AM, Daniel Gl?ckner [off-list ref] wrote:

On Mon, Oct 15, 2012 at 10:30:15PM +0200, Linus Walleij wrote:

quoted

Another patch that is circulating concerns edge triggers and similar,
and it appear that some parts of the GPIO sysfs is for example
redefining and exporting IRQchip properties like trigger edge
in sysfs, while the settings of the irqchip actually used by the driver
is not reflected in the other direction. So you can *set* these things
by writing in the GPIO sysfs, but never trust what you *read* from
there. And you can set what edges an IRQ will trigger on a certain
GPIO, and the way to handle the IRQs from usespace is to poll
on a value. This is not really documented but well ...

Part of this sounds like you are not familiar with the GPIOlib sysfs
IRQ stuff.

Yeah you bet :-)

I'm just trying to maintain it, I think I need your help with this.

Do you think it'd be possible for you to augment the
Documentation/gpio.txt file with some userspace code examples?
I think this could be very useful.

The trigger edge set in sysfs is only used when userspace
polls the GPIO via sysfs. Drivers that want to register a gpio IRQ
should IMHO always explicitly request the edge/level to trigger on and
they should request the gpio beforehand. This prevents the gpio from
being exported to userspace. Only IRQ triggers accepted by the irq chip
are settable in sysfs, so you can trust the value read from that file.

OK.

quoted

Daniel: are you interested in helping us fixing the GPIOlib
sysfs ABI and kernel internals? I'm a bit afraid of it.

Actually I don't know what you want to change to fix the existing sysfs
ABI. Personally I'd like to see the following things changed:
 - /sys/gpio/.../direction does not correspond to hardware before first
   use of gpio_direction_* due to lack of gpio_get_direction.
 - Names given to gpios by the chip should just result in symlinks to
   the usual gpioX directories or (un)exporting of gpios should accept
   names.

Please send a patch! I'll merge.

Actually I'm mostly referring to another floating patch, I will try to
dig it up and CC you.

Yours,
Linus Walleij