On Mon, Apr 28, 2025 at 02:15:12PM -0700, Doug Anderson wrote: Hello Jayesh,
> Hi, > > On Thu, Apr 24, 2025 at 6:32 PM Kumar, Udit <u-kum...@ti.com> wrote: > > > > Hello Jayesh, > > > > On 4/24/2025 4:24 PM, Jayesh Choudhary wrote: > > > For TI SoC J784S4, the display pipeline looks like: > > > TIDSS -> CDNS-DSI -> SN65DSI86 -> DisplayConnector -> DisplaySink > > > This requires HPD to detect connection form the connector. > > > By default, the HPD is disabled for eDP. So enable it conditionally > > > based on a new flag 'keep-hpd' as mentioned in the comments in the > > > driver. > > > > > > Signed-off-by: Jayesh Choudhary <j-choudh...@ti.com> > > > --- > > > > > > Hello All, > > > > > > Sending this RFC patch to get some thoughts on hpd for sn65dsi86. > > > > > > Now that we have a usecase for hpd in sn65dsi86, I wanted to get > > > some comments on this approach to "NOT DISABLE" hpd in the bridge. > > > As the driver considers the eDP case, it disables hpd by default. > > > So I have added another property in the binding for keeping hpd > > > functionality (the name used is still debatable) and used it in > > > the driver. > > > > > > Is this approach okay? > > > Also should this have a "Fixes" tag? > > > > > > > > .../bindings/display/bridge/ti,sn65dsi86.yaml | 6 ++++++ > > > drivers/gpu/drm/bridge/ti-sn65dsi86.c | 14 +++++++++----- > > > 2 files changed, 15 insertions(+), 5 deletions(-) > > > > > > diff --git > > > a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > > b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > > index c93878b6d718..5948be612849 100644 > > > --- a/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > > +++ b/Documentation/devicetree/bindings/display/bridge/ti,sn65dsi86.yaml > > > @@ -34,6 +34,12 @@ properties: > > > Set if the HPD line on the bridge isn't hooked up to anything or > > > is > > > otherwise unusable. > > > > > > + keep-hpd: > > > + type: boolean > > > + description: > > > + HPD is disabled in the bridge by default. Set it if HPD line makes > > > + sense and is used. > > > + > > > > Here are my suggestions > > > > 1) use interrupt in binding as optional instead of keep-hpd > > > > 2) use interrupt field (if present to enable of disable HPD functions in > > driver) > > Officially we've already got a "no-hpd" specified in the device tree. > You're supposed to be specifying this if HPD isn't hooked up. It would > be best if we could use that property if possible. If we think that > using the lack of "no-hpd" will break someone then we should be > explicit about that. > > I'd also note that unless you've figured out a way to turn off the > awful debouncing that ti-sn65dsi86 does on HPD that using HPD (at > least for initial panel power on) only really makes sense for when > we're using ti-sn65dsi86 in "DP" mode. For initial eDP panel poweron > it was almost always faster to just wait the maximum delay of the > panel than to wait for ti-sn65dsi86 to finally report that HPD was > asserted. > > I could also note that it's possible to use the ti-sn65dsi86's "HPD" > detection even if the interrupt isn't hooked up, so I don't totally > agree with Udit's suggestion. > > I guess the summary of my thoughts then: If you want to enable HPD for > eDP, please explain why in the commit message. Are you using this to > detect "panel interrupt"? Somehow using it for PSR? Using it during > panel power on? If using it for panel power on, have you confirmed > that this has a benefit compared to using the panel's maximum delay? > > -Doug I'm working on a similar issue where the bridge is used to provide a connector to a display port monitor and hot pluging would be needed. Related, but not the issue here: We have two display outputs and the reported connected display without an actual monitor to report a video mode then confuses the system to also not use the second display. As I already have a solution which fixes my issue, hopefully not affecting the eDP use case a proposed that here: https://lore.kernel.org/all/20250501074805.3069311-1-max.oss...@gmail.com/ Regards, Max
