Hi Doug, Thank you for the patch. On Thu, Apr 30, 2020 at 12:46:16PM -0700, Douglas Anderson wrote: > The ti-sn65dsi86 MIPI DSI to eDP bridge chip has a dedicated hardware > HPD (Hot Plug Detect) pin on it, but it's mostly useless for eDP > because of excessive debouncing in hardware. Specifically there is no > way to disable the debouncing and for eDP debouncing hurts you because > HPD is just used for knowing when the panel is ready, not for > detecting physical plug events. > > Currently the driver in Linux just assumes that nobody has HPD hooked > up. It relies on folks setting the "no-hpd" property in the panel > node to specify that HPD isn't hooked up and then the panel driver > using this to add some worst case delays when turning on the panel. > > Apparently it's also useful to specify "no-hpd" in the bridge node so > that the bridge driver can make sure it's doing the right thing > without peeking into the panel [1]. This would be used if anyone ever > found it useful to implement support for the HW HPD pin on the bridge. > Let's add this property to the bindings. > > NOTES: > - This is somewhat of a backward-incompatible change. All current > known users of ti-sn65dsi86 didn't have "no-hpd" specified in the > bridge node yet none of them had HPD hooked up. This worked because > the current Linux driver just assumed that HPD was never hooked up. > We could make it less incompatible by saying that for this bridge > it's assumed HPD isn't hooked up _unless_ a property is defined, but > "no-hpd" is much more standard and it's unlikely to matter unless > someone quickly goes and implements HPD in the driver. > - It is sensible to specify "no-hpd" at the bridge chip level and > specify "hpd-gpios" at the panel level. That would mean HPD is > hooked up to some other GPIO in the system, just not the hardware > HPD pin on the bridge chip. > > [1] https://lore.kernel.org/r/20200417180819.GE5861@xxxxxxxxxxxxxxxxxxxxxxxxxx > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx> > Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > --- > > Changes in v4: > - Tacked on "or is otherwise unusable." to description. > > Changes in v3: > - useful implement => useful to implement > > Changes in v2: > - ("dt-bindings: drm/bridge: ti-sn65dsi86: Document no-hpd") new for v2. > > .../devicetree/bindings/display/bridge/ti,sn65dsi86.yaml | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > index 6d7d40ad45ac..75c4e8b8e4b7 100644 > --- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > +++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > @@ -28,6 +28,12 @@ properties: > maxItems: 1 > description: GPIO specifier for GPIO1 pin on bridge (active low). > > + no-hpd: > + type: boolean > + description: > + Set if the HPD line on the bridge isn't hooked up to anything or is > + otherwise unusable. > + > vccio-supply: > description: A 1.8V supply that powers the digital IOs. > > @@ -207,6 +213,8 @@ examples: > clocks = <&rpmhcc RPMH_LN_BB_CLK2>; > clock-names = "refclk"; > > + no-hpd; > + > ports { > #address-cells = <1>; > #size-cells = <0>; -- Regards, Laurent Pinchart
