On Mon, 24 May 2021 17:01:49 -0700, Douglas Anderson wrote:
The HPD (Hot Plug Detect) signal is present in many (probably even "most") eDP panels. For eDP, this signal isn't actually used for detecting hot-plugs of the panel but is more akin to a "panel ready" signal. After you provide power to the panel, panel timing diagrams typically say that you should wait for HPD to be asserted (or wait a fixed amount of time) before talking to the panel.
The panel-simple bindings describes many eDP panels and many of these panels provide the HPD signal. We should add the HPD-related properties to the panel-simple bindings. The HPD properties are actually defined in panel-common.yaml, so adding them here just documents that they are OK for panels handled by the panel-simple bindings.
NOTE: whether or not we'd include HPD properties in the panel node is more a property of the board design than the panel itself. For most boards using these eDP panels everything "magically" works without specifying any HPD properties and that's been why we haven't needed to allow the HPD properties earlier. On these boards the HPD signal goes directly to a dedicated "HPD" input to the eDP controller and this connection doesn't need to be described in the device tree. The only time the HPD properties are needed in the device tree are if HPD is hooked up to a GPIO or if HPD is normally on the panel but isn't used on a given board. That means that if we don't allow the HPD properties in panel-simple then one could argue that we've got to boot all eDP panels (or at least all those that someone could conceivably put on a system where HPD goes to a GPIO or isn't hooked up) from panel-simple.
Signed-off-by: Douglas Anderson dianders@chromium.org
Changes in v8:
- Explain better why HPD needs to be in panel-simple in commit msg.
Changes in v7:
- List hpd properties bindings patch new for v7.
.../devicetree/bindings/display/panel/panel-simple.yaml | 2 ++ 1 file changed, 2 insertions(+)
Reviewed-by: Rob Herring robh@kernel.org