On Friday, February 18th, 2022 at 11:38, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > What I'm reading in the above is that it is being considered to allow > changing the panel-orientation value after the connector has been made > available to userspace; and let userspace know about this through a uevent. > > I believe that this is a bad idea, it is important to keep in mind here > what userspace (e.g. plymouth) uses this prorty for. This property is > used to rotate the image being rendered / shown on the framebuffer to > adjust for the panel orientation. > > So now lets assume we apply the correct upside-down orientation later > on a device with an upside-down mounted LCD panel. Then on boot the > following could happen: > > 1. amdgpu exports a connector for the LCD panel to userspace without > setting panel-orient=upside-down > 2. plymouth sees this and renders its splash normally, but since the > panel is upside-down it will now actually show upside-down At this point amdgpu hasn't probed the connector yet. So the connector will be marked as disconnected, and plymouth shouldn't render anything. > 3. amdgpu adjusts the panel-orient prop to upside-down, sends out > uevents That's when amdgpu marks the connector as connected. So everything should be fine I believe, no bad frame. > 4. Lets assume plymouth handles this well (i) and now adjust its > rendering and renders the next frame of the bootsplash 180° rotated > to compensate for the panel being upside down. Then from now on > the user will see the splash normally > > So this means that the user will briefly see the bootsplash rendered > upside down which IMHO is not acceptable behavior. Also see my footnote > about how I seriously doubt plymouth will see the panel-orient change > at all. > > I'm also a bit unsure about: > > a) How you can register the panel connector with userspace before > reading the edid, don't you need the edid to give the physical size + > modeline to userspace, which you cannot just leave out ? Yup. The KMS EDID property is created before the EDID is read, and is set to zero (NULL blob). The width/height in mm and other info are also zero. You can try inspecting the state printed by drm_info on any disconnected connector to see for yourself. > I guess the initial modeline is inherited from the video-bios, but > what about the physical size? Note that you cannot just change the > physical size later either, that gets used to determine the hidpi > scaling factor in the bootsplash, and changing that after the initial > bootsplash dislay will also look ugly > > b) Why you need the edid for the panel-orientation property at all, > typically the edid prom is part of the panel and the panel does not > know that it is mounted e.g. upside down at all, that is a property > of the system as a whole not of the panel as a standalone unit so > in my experience getting panel-orient info is something which comes > from the firmware /video-bios not from edid ? This is an internal DRM thing. The orientation quirks logic uses the mode size advertised by the EDID. I agree that at least in the Steam Deck case it may not make a lot of sense to use any info from the EDID, but that's needed for the current status quo. Also note, DisplayID has a bit to indicate the panel orientation IIRC. Would be nice to support parsing this at some point.
