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

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Message-ID: <1903581972.81288.e9d48a65-997b-4986-a9d0-10632895df40.open-xchange@email.1und1.de>
Date:   Fri, 23 Sep 2016 20:39:01 +0200 (CEST)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Eric Anholt <eric@...olt.net>
Cc:     linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        bcm-kernel-feedback-list@...adcom.com,
        Mark Rutland <mark.rutland@....com>,
        Alexandre Courbot <gnurou@...il.com>,
        linux-rpi-kernel@...ts.infradead.org,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] dt-bindings: Add a binding for the RPi firmware
 GPIO driver.

Hi Eric,

> Eric Anholt <eric@...olt.net> 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@...olt.net>
> ---
>  .../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.

> +- gpio-controller:	Marks the device node as a gpio controller
> +- #gpio-cells:		Should be <2> for GPIO number and flags
> +- ngpios:		Number of GPIO lines to control.  See gpio.txt
> +- firmware:		Reference to the RPi firmware device node
> +- raspberrypi,firmware-gpio-offset:
> +			Number the firmware uses for the first GPIO line
> +			  controlled by this driver

We should avoid such properties because they don't really describe the hardware.

Stefan