1. Jun 12, 2021
    • Douglas Anderson's avatar
      dt-bindings: display: simple: List hpd properties in panel-simple · 557acb5f
      Douglas Anderson authored
      
      
      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: default avatarDouglas Anderson <dianders@chromium.org>
      Reviewed-by: default avatarRob Herring <robh@kernel.org>
      Link: https://patchwork.freedesktop.org/patch/msgid/20210611101711.v10.1.Ieb731d23680db4700cc41fe51ccc73ba0b785fb7@changeid
      557acb5f
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