On Mon, 22 Apr 2024, Michael Olbrich <m.olbrich@xxxxxxxxxxxxxx> wrote: > Hi, > > In short: I have a HDMI monitor attached to Intel graphics. I'm trying to > set a non-CEA mode but the driver always maps it to the corresponding CEA > mode. Please file a bug as described at [1], and attach dmesg with debugs enabled, so we can see what's going on and what kernel and hardware you're using exactly, and so on. BR, Jani. [1] https://drm.pages.freedesktop.org/intel-docs/how-to-file-i915-bugs.html > > More specifically, the monitor has two 1920x1080@60 modes in the EDID: > 1. The CEA mode with VIC 16 > 2. A custom DTD mode with exactly the same timings (this is the preferred > mode). > > From a userspace perspective, the two modes are mostly identical, except > for the 16:9 aspect ratio flag in the CEA mode and the preferred type in > the other. > > I want to select the second (preferred) mode, but that does not seem > possible: > intel_hdmi_compute_avi_infoframe() tries to determine which VIC should be > added to the avi infoframe and if limited or full range is used. > It uses various DRM helpers here but in the end drm_match_cea_mode() is > called. And here lies the problem: > The mode provided by the userspace has explicitly no aspect ratio. But > here, it is interpreted as "the aspect ration is undefined". So matching > ignored the aspect ratio and the CEA mode with VIC 16 is found and limited > range is used. > > The commit that introduces this fuzzy matching > 357768cc9e3fdacf6551da0ae1483bc87dbcb4e8 ("drm/edid: Fix cea mode aspect > ratio handling") made sense at the time. The capability > DRM_CLIENT_CAP_ASPECT_RATIO that exposes aspect ratios to userspace was > introduced later in the same merge request, from what I can tell > 7595bda2fb4378ccbb8db1d0e8de56d15ea7f7fa ("drm: Add DRM client cap for > aspect-ratio"). > > Am I missing something here, or is it just not possible to select the > non-CEA mode right now? In my specific example, the selected CEA mode is > actually supported by the monitor, but as far as I can tell, the CEA mode > is used even if the monitor does not support it at all. > > I've only tested this on Intel, but I assume that other drivers that use > the same helpers have the same problem. > > So how can this be fixed? I've considered matching the aspect ratio based > on the DRM_CLIENT_CAP_ASPECT_RATIO capability, but I'm not sure if that is > valid. The documentation is limited and I found nothing that describes what > the userspace should do here. > Or would a new capability make sense here? Or something entirely different? > I'm not sure how I should proceed here. Any help would be appreciated. > > Regards, > Michael -- Jani Nikula, Intel
