[RFC PATCH 09/13] dt-bindings: drm/tegra: Add DPAUX pinctrl documentation

[Thierry Reding]

On Fri, Jun 17, 2016 at 01:03:43PM +0100, Jon Hunter wrote:
> On Tegra124, Tegra132 and Tegra210 devices the pads used by the Display
> Port Auxiliary (DPAUX) channel are multiplexed such that they can also
> be used by one of the internal i2c controllers. Note that this is
> different from i2c-over-AUX supported by the DPAUX controller. The
> register that configures these pads is part of the DPAUX controllers
> register set and so a pinctrl driver is being added for the DPAUX device
> to share these pads. Add the device-tree binding documentation for the
> DPAUX pad controller.

There are a couple more "i2c" vs. "I2C" in the above. Please use the
latter consistently.

Also the subject line should be something different. drm is a linuxism
and hence shouldn't be used anywhere near DT bindings.

> Please note that although the "off" function for the DPAUX pads is not
> technically a pin-mux setting but more of a pin-conf setting it is
> simpler to expose these as a function so that the user can simply select
> either "aux", "i2c" or "off" as the current function/mode.
> 
> Update the main DPAUX binding documentation to reference the DPAUX pad
> controller binding document and add the 'i2c-bus' subnode. The 'i2c-bus'
> subnode is used for populating I2C slaves for the DPAUX device so that
> the I2C driver core does not attempt to add the DPAUX pad controller
> nodes as I2C slaves.
> 
> Signed-off-by: Jon Hunter <jonathanh at nvidia.com>
> ---
>  .../display/tegra/nvidia,tegra20-host1x.txt        |  4 ++
>  .../pinctrl/nvidia,tegra124-dpaux-padctl.txt       | 60 ++++++++++++++++++++++
>  2 files changed, 64 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pinctrl/nvidia,tegra124-dpaux-padctl.txt
> 
> diff --git a/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.txt b/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.txt
> index 361a472eac4b..6759554b7b8f 100644
> --- a/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.txt
> +++ b/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.txt
> @@ -242,6 +242,10 @@ of the following host1x client modules:
>    - reset-names: Must include the following entries:
>      - dpaux
>    - vdd-supply: phandle of a supply that powers the DisplayPort link
> +  - i2c-bus: Subnode where I2C slave devices should be listed.

Should we perhaps say at this point that the subnode should always be
added, oven if empty? Otherwise we'll still run into a conflict with the
pinmux nodes.

> +
> +  See ../pinctrl/nvidia,tegra124-dpaux-padctl.txt for information
> +  regarding the DPAUX pad controller bindings.
>  
>  Example:
>  
> diff --git a/Documentation/devicetree/bindings/pinctrl/nvidia,tegra124-dpaux-padctl.txt b/Documentation/devicetree/bindings/pinctrl/nvidia,tegra124-dpaux-padctl.txt
> new file mode 100644
> index 000000000000..3be0ced01680
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pinctrl/nvidia,tegra124-dpaux-padctl.txt
> @@ -0,0 +1,60 @@
> +Device tree binding for NVIDIA Tegra DPAUX pad controller
> +========================================================
> +
> +The Tegra Display Port Auxiliary (DPAUX) pad controller manages two pins
> +which can be assigned to either the DPAUX channel or to an I2C
> +controller.
> +
> +This document defines the device-specific binding for the DPAUX pad
> +controller. Refer to pinctrl-bindings.txt in this directory for generic
> +information about pin controller device tree bindings. Please refer to
> +the binding document ../display/tegra/nvidia,tegra20-host1x.txt for more
> +details on the DPAUX binding.
> +
> +Pin muxing:
> +-----------
> +
> +Child nodes contain the pinmux configurations following the conventions
> +from the pinctrl-bindings.txt document.
> +
> +Since only three configurations are possible, only three child nodes are
> +needed to describe the pin mux'ing options for the DPAUX pads.
> +Furthermore, given that the pad functions are only applicable to a
> +single set of pads, the child nodes do not need to describe the pads the
> +functions are being applied to.
> +
> +Required properties:
> +- groups: Must be "dpaux-io"

Above you say that we don't need to describe the pads, but then the
groups property does describe the pads. Why?

Thierry
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