On Wed, Feb 23, 2022 at 10:20:18AM -0800, Doug Anderson wrote: > On Wed, Feb 23, 2022 at 10:05 AM Kieran Bingham wrote: > > > > > > > + /* For DisplayPort, disable scrambling mode. */ > > > > > + if (pdata->bridge.type == DRM_MODE_CONNECTOR_DisplayPort) > > > > > + regmap_update_bits(pdata->regmap, SN_TRAINING_SETTING_REG, > > > > > + SCRAMBLE_DISABLE, SCRAMBLE_DISABLE); > > > > > > > > I'm assuming that this is the important part of your patch? Would be > > > > sorta nice to include the "why" in your comment. Why do you want to > > > > disable scrambling mode for DP but not for eDP? Maybe you care about > > > > compatibility but not EMI if you're hooking up to random DP things? > > > > > > I'll investigate and include proper documentation in v2 (or drop the > > > change altogether if it's not required). > > > > And indeed, this part is important. If I drop this hunk - then I get no > > display output. > > > > I'm afraid I don't (yet) know the reasons 'why' to extend the comment, > > beyond "Scrambling is not supported for DP". > > > > If anyone already does, please feel free to provide the text, and I'll > > include it in the next revision, or I'll try to do some more digging > > into this part. > > I don't know _tons_ about it, but I later learned that the "alternate" > scrambler is used for eDP and the normal scrambler is used for DP. I > don't have any background about why they are different other than what > looks to be intentionally making the two things incompatible. I think it was done for DRM purpose, to prevent signals meant for a panel to be connected to a device that could capture video from a DP source. > ...so I guess that would make it pretty clear why you can't use the > alternate scrambler for DP. I haven't personally done the research to > know if you can be officially DP compliant with the scrambler > disabled. I also don't know why the ti-sn65dsi86 makes it so difficult > to switch to the standard scrambler or if it works at all... ;-) -- Regards, Laurent Pinchart
