GPIO sysfs 'default' values

GPIO sysfs 'default' values

[Tony Prisk]

Hi Grant, Linus.

I was testing our new gpio/pinctrl driver today and noticed something a
little weird.

I exported gpio0 via sysfs and echoed the direction value - it was 'in'.
This pin is used to control an LCD panel, and is actually in 'out' mode.
If I write 'in' to direction, it changes mode to 'in' and the panel
turns off. Setting it back to 'out' and value=0, and the panel turns on
again.

I noticed that I had no gpiochip->get_direction, so I added it, but the
result was the same.

Any idea what I've missed?

Regards
Tony Prisk

GPIO sysfs 'default' values

[Tony Prisk]

On Thu, 2013-02-21 at 20:11 +1300, Tony Prisk wrote:
> Hi Grant, Linus.
> 
> I was testing our new gpio/pinctrl driver today and noticed something a
> little weird.
> 
> I exported gpio0 via sysfs and echoed the direction value - it was 'in'.
> This pin is used to control an LCD panel, and is actually in 'out' mode.
> If I write 'in' to direction, it changes mode to 'in' and the panel
> turns off. Setting it back to 'out' and value=0, and the panel turns on
> again.
> 
> I noticed that I had no gpiochip->get_direction, so I added it, but the
> result was the same.
> 
> Any idea what I've missed?
> 
> Regards
> Tony Prisk

Sorted it out.
->get_direction was all that was needed.

Apologies,
Tony P

GPIO sysfs 'default' values

[Lothar Waßmann]

Hi,

Tony Prisk writes:
> Hi Grant, Linus.
> 
> I was testing our new gpio/pinctrl driver today and noticed something a
> little weird.
> 
> I exported gpio0 via sysfs and echoed the direction value - it was 'in'.
> This pin is used to control an LCD panel, and is actually in 'out' mode.
> If I write 'in' to direction, it changes mode to 'in' and the panel
> turns off. Setting it back to 'out' and value=0, and the panel turns on
> again.
> 
> I noticed that I had no gpiochip->get_direction, so I added it, but the
> result was the same.
> 
> Any idea what I've missed?
> 
You missed to report on what platform this happens.
The platform specific GPIO driver obviously does not initialize the
shadow variables for the hardware registers correctly.


Lothar Wa?mann
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