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

Laurent Pinchart
2017-05-16T16:54:25Z

Hi Eric,

On Tuesday 16 May 2017 09:47:49 Eric Anholt wrote:
> Rob Herring <robh+dt@kernel.org> writes:
> > On Mon, May 15, 2017 at 7:03 PM, Eric Anholt <eric@anholt.net> wrote:
> >> Laurent Pinchart <laurent.pinchart@ideasonboard.com> writes:
> >>> Hi Eric,
> >>>
> >>> Thank you for the patch.
> >>>
> >>> On Thursday 11 May 2017 16:56:23 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-touc
> >>>> hscreen-bridge.txt create mode 100644
> >>>> Documentation/devicetree/bindings/display/panel/raspberrypi,7inch-touch
> >>>> screen-panel.txt
> >>>>
> >>>> diff --git
> >>>> a/Documentation/devicetree/bindings/display/bridge/raspberrypi,7inch-to
> >>>> uchscreen-bridge.txt
> >>>> b/Documentation/devicetree/bindings/display/bridge/raspberrypi,7inch-to
> >>>> uchscreen-bridge.txt new file mode 100644
> >>>> index 000000000000..a5669beaf68f
> >>>> --- /dev/null
> >>>> +++
> >>>> b/Documentation/devicetree/bindings/display/bridge/raspberrypi,7inch-to
> >>>> uchscreen-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
> >>>> +
> >>>> +and this covers the TC358762 bridge and Atmel microcontroller, while
> >>>> +../panel/raspberrypi,7inch-touchscreen-panel.txt covers the panel.
> >>>
> >>> The TC358762 is a standalone bridge that doesn't depend on the ATTiny
> >>> microcontroller used by the RPI. As it's usable standalone, I believe
> >>> this binding should be split in two.
> >>
> >> Do you have a plan for how I would implement a driver on top of that
> >> binding change, though? Note that we don't program the Toshiba
> >> directly, we only send commands to the Atmel.
> >
> > I agree. If it is a black box and the interface to the host is defined
> > by the Atmel uC firmware, then that's what the DT should describe.
> > Perhaps a diagram here or pointer to one would help and remove
> > mentioning what kind of bridge chip it is.
>
> It's a *very* black box. I have some non-public schematics that don't
> even say what panel is involved, and no documentation of the uc
> interface. The driver code is just replicating the firmware's
> programming sequence.
>
> I would certainly love to be building a generic TC358762 driver, which
> would be a lot more satisfying. I just don't think it's doable for this
> panel. Given that, what do I need to do to the DT? Should I just drop
> mention of the Toshiba and talk about this being a bridge with a custom
> microcontroller firmware?

I think that would be best, yes. Could you share a simple block-diagram of the
hardware ? It would help turning my random advices into semi-random advices
:-)

--
Regards,

Laurent Pinchart