Re: [PATCH 1/3] dt-bindings: Add a binding for the RPi firmware GPIO driver.

[Stefan Wahren]

> Stephen Warren <swarren@xxxxxxxxxxxxx> hat am 26. September 2016 um 18:38
> geschrieben:
> 
> 
> On 09/23/2016 12:39 PM, Stefan Wahren wrote:
> > Hi Eric,
> >
> >> Eric Anholt <eric@xxxxxxxxxx> hat am 19. September 2016 um 18:13
> >> geschrieben:
> >>
> >>
> >> The RPi firmware exposes all of the board's GPIO lines through
> >> property calls.  Linux chooses to control most lines directly through
> >> the pinctrl driver, but for the FXL6408 GPIO expander on the Pi3, we
> >> need to access them through the firmware.
> >>
> >> Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
> >> ---
> >>  .../bindings/gpio/gpio-raspberrypi-firmware.txt    | 22
> >> ++++++++++++++++++++++
> >>  1 file changed, 22 insertions(+)
> >>  create mode 100644
> >> Documentation/devicetree/bindings/gpio/gpio-raspberrypi-firmware.txt
> >>
> >> diff --git
> >> a/Documentation/devicetree/bindings/gpio/gpio-raspberrypi-firmware.txt
> >> b/Documentation/devicetree/bindings/gpio/gpio-raspberrypi-firmware.txt
> >> new file mode 100644
> >> index 000000000000..2b635c23a6f8
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/gpio/gpio-raspberrypi-firmware.txt
> >> @@ -0,0 +1,22 @@
> >> +Raspberry Pi power domain driver
> >> +
> >> +Required properties:
> >> +
> >> +- compatible:		Should be "raspberrypi,firmware-gpio"
> >
> > i think the compatible should be more specific like
> >
> > raspberrypi,rpi3-firmware-gpio
> >
> > and all information which aren't requestable from the firmware should be
> > stored
> > in a info structure. This makes the driver easier to extend in the future by
> > adding new compatibles and their info structures.
> 
> Is this actually specific to the Pi3 at all? 

AFAIK only the Raspberry Pi 3 has a GPIO expander which is accessible via the
common FW. My suggestion tries to follow the basic guideline "A precise
compatible string is better than a vague one" from Device Tree for Dummies [1].
So in case the next Raspberry Pi would have a different GPIO expander with
different parameters we could add a new compatible.

But you are right the word order in "rpi3-firmware-gpio" suggests that there are
different FW which is wrong. At the end it's only a compatible string. So no
strong opinion about the naming.

[1] -
https://events.linuxfoundation.org/sites/events/files/slides/petazzoni-device-tree-dummies.pdf

> Isn't the FW the same 
> across all Pis; the part that's specific to the Pi3 is whether it's 
> useful to use that API?
> 
> As such, I'd suggest just raspberrypi,firmware-gpio as the compatible value.
>