Re: [PATCH 2/4] dt-bindings: Document the Raspberry Pi Touchscreen nodes.

Laurent Pinchart
2017-05-15T21:56:06Z

Hi Rob,

On Monday 15 May 2017 15:44:57 Rob Herring wrote:
> On Thu, May 11, 2017 at 04:56:23PM -0700, Eric Anholt wrote:
> > The Raspberry Pi 7" Touchscreen is a DPI touchscreen panel with
> > DSI->DPI bridge and touchscreen controller integrated, that connects
> > to the Raspberry Pi through its 15-pin "DSI" connector (some lines are
> > DSI, some lines are I2C).
> >
> > This device is represented in the DT as three nodes (DSI device, I2C
> > device, panel). Input will be left to a separate binding later, as it
> > will be a basic I2C client device.
> >
> > Signed-off-by: Eric Anholt <eric@anholt.net>
> > ---
> >
> > .../raspberrypi,7inch-touchscreen-bridge.txt | 68
> > ++++++++++++++++++++++ .../panel/raspberrypi,7inch-touchscreen-panel.txt
> > | 7 +++
> > 2 files changed, 75 insertions(+)
> > create mode 100644
> > Documentation/devicetree/bindings/display/bridge/raspberrypi,7inch-touch
> > screen-bridge.txt create mode 100644
> > Documentation/devicetree/bindings/display/panel/raspberrypi,7inch-touchs
> > creen-panel.txt>
> > diff --git
> > a/Documentation/devicetree/bindings/display/bridge/raspberrypi,7inch-touc
> > hscreen-bridge.txt
> > b/Documentation/devicetree/bindings/display/bridge/raspberrypi,7inch-touc
> > hscreen-bridge.txt new file mode 100644
> > index 000000000000..a5669beaf68f
> > --- /dev/null
> > +++
> > b/Documentation/devicetree/bindings/display/bridge/raspberrypi,7inch-touc
> > hscreen-bridge.txt @@ -0,0 +1,68 @@
> > +Official 7" (800x480) Raspberry Pi touchscreen panel's bridge.
> > +
> > +This DSI panel contains:
> > +
> > +- TC358762 DSI->DPI bridge
> > +- Atmel microcontroller on I2C for power sequencing the DSI bridge and
> > + controlling backlight
> > +- Touchscreen controller on I2C for touch input
>
> This is 1 uC or 2?
>
> > +
> > +and this covers the TC358762 bridge and Atmel microcontroller, while
> > +../panel/raspberrypi,7inch-touchscreen-panel.txt covers the panel.
> > +
> > +Required properties:
> > +- compatible: Must be "raspberrypi,7inch-touchscreen-bridge"
> > +- raspberrypi,touchscreen-bridge:
> > + Handle to the I2C device for Atmel microcontroller
> > +
> > +Example:
> > +
> > +dsi1: dsi@7e700000 {
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > + <...>
> > +
> > + lcd-bridge@0 {
> > + compatible = "raspberrypi,7inch-touchscreen-bridge";
> > + reg = <0>;
> > +
> > + raspberrypi,touchscreen-bridge = <&pitouchscreen_bridge>;
>
> I think this should be a port with a graph connection from the DSI
> node to the i2c bridge device (and then to the panel).

No, this should actually not exist :-) The property references the I2C device
DT node corresponding to the microcontroller that controls the backlight (and,
if I understand correctly, handles power sequencing). The DSI driver (in patch
3/4) then grabs the I2C device and talks to it. I don't think this is right,
as commented separately on this patch, the bindings should be split, with a
standalone binding for the TC358762 (and a separate standalone driver too).

> It's also how other DSI bridges like the tc358767 are done.
>
> > + ports {
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > + port@0 {
> > + reg = <0>;
>
> BTW, you don't need this when there is only 1.
>
> > + pitouchscreen_bridge_port: endpoint {
> > + remote-endpoint =
<&pitouchscreen_panel_port>;
> > + };
> > + };
> > + };
> > + };
> > +};
> > +
> > +i2c_dsi: i2c {
> > + compatible = "i2c-gpio";
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > + gpios = <&gpio 28 0
> > + &gpio 29 0>;
> > +
> > + pitouchscreen_bridge: bridge@45 {
> > + compatible = "raspberrypi,touchscreen-bridge-i2c";
> > + reg = <0x45>;
> > + };
> > +};
> > +
> > +lcd {
> > + compatible = "raspberrypi,7inch-touchscreen-panel";
> > + ports {
> > + #address-cells = <1>;
> > + #size-cells = <0>;
> > + port@0 {
> > + reg = <0>;
> > + pitouchscreen_panel_port: endpoint {
> > + remote-endpoint =
<&pitouchscreen_bridge_port>;
> > + };
> > + };
> > + };
> > +};
> > diff --git
> > a/Documentation/devicetree/bindings/display/panel/raspberrypi,7inch-touch
> > screen-panel.txt
> > b/Documentation/devicetree/bindings/display/panel/raspberrypi,7inch-touch
> > screen-panel.txt new file mode 100644
> > index 000000000000..1e84f97b3b20
> > --- /dev/null
> > +++
> > b/Documentation/devicetree/bindings/display/panel/raspberrypi,7inch-touch
> > screen-panel.txt @@ -0,0 +1,7 @@
> > +Official 7" (800x480) Raspberry Pi touchscreen panel's panel.
> > +
> > +This binding is compatible with the simple-panel binding, which is
> > specified +in simple-panel.txt in this directory.
> > +
> > +Required properties:
> > +- compatible: Must be "raspberrypi,7inch-touchscreen-panel"

--
Regards,

Laurent Pinchart