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@xxxxxxxxxxxx> > --- > > 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@xxxxxxxxxx>
