Re: [PATCH] HID: cp2112: fix gpio value in gpio_direction_output

[Jiri Kosina <jkosina@suse.cz>]

On Mon, 7 Jul 2014, Benjamin Tissoires wrote:

> > CP2112 does not offer an atomic method to set both gpio
> > direction and value.
> > Also it does not permit to set gpio value before putting
> > gpio in output. In fact, accordingly to Silicon Labs
> > AN495, Rev. 0.2, cpt. 4.4, the HID report to set gpio
> > values "does not affect any pins that are not configured
> > as outputs".
> >
> > This is confirmed on evaluation board CP2112-EK.
> > With current driver, after execute:
> >         echo in > /sys/class/gpio/gpio248/direction
> >         echo low > /sys/class/gpio/gpio248/direction
> > gpio output is still high. Only after a following
> >         echo low > /sys/class/gpio/gpio248/direction
> > gpio output gets low.
> >
> > Fix driver by changing order of operations; first set
> > direction then set value.
> >
> > The drawback of this new sequence is that we can have
> > a pulse on gpio pin when direction is changed from
> > input to output-low, but this cannot be avoided on
> > current CP2112.
> 
> In this case, does keeping the first cp2112_gpio_set() before setting
> the output direction prevents the pulse?
> If so, then you can just keep the current code, and simply add the
> cp2112_gpio_set() at the end of cp2112_gpio_direction_output().
> 
> In both case, this is:
> Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

I am queuing this for 3.17, thanks.

-- 
Jiri Kosina
SUSE Labs