On Thu, Feb 11, 2021 at 4:12 PM Mario Kleiner <mario.kleiner.de@xxxxxxxxx> wrote: > > On Wed, Feb 10, 2021 at 10:36 PM Alex Deucher <alexdeucher@xxxxxxxxx> wrote: >> >> On Wed, Feb 10, 2021 at 4:08 PM Mario Kleiner >> <mario.kleiner.de@xxxxxxxxx> wrote: >> > >> > Resending this one as well, in the hope of some clarification or background information. >> > >> > > Thanks Alex. > >> I suspect this may have been a limitation from DCE11.0 (E.g., >> carrizo/stoney APUs). They had some bandwidth limitations with >> respect to high bit depth IIRC. I suspect it should be fine on the >> relevant dGPUs. The code was probably originally added for the APUs > > > That sounds as if it would make sense for me to try to submit a patch to you that restricts this limitation to DCE 11.0 only? I suspect older DCE 8.x APUs have similar limitations. Although it may only be an issue with multiple monitors or something like that. I don't remember the details. @Harry Wentland do you remember? > > All i can say is during my testing with DCE-8.3 over HDMI and DCE-11.2 over DP under amdvlk with fp16 mode and ouptut_bpc set to 10 bpc, ie. dithering down from 12 bpc to 10 bpc, i didn't notice any problems when hacking this out, and photometer measurements showed good improvements of luminance reproduction with dithering. > >> and just never updated or the changes were accidentally lost when we >> consolidated the DCE code. Unfortunately, there are not a lot of apps >> that work properly in Linux with >8 bits per channel. >> > > Mine does ;-). As does apparently the Kodi media player. And at least Gnome/X11 works now, whereas KDE's Kwin/X11 used to work nicely, but regressed. And amdvlk does have fp16 support now since a while ago, so that's one way to get high precision without disturbing conventional desktop apps. I'll probably look into Mesa's Vulkan/WSI for 10 bpc / fp16 sometime this year if nobody beats me to it. > Sounds good. Alex > -mario > > >> Alex >> >> >> > Thanks, >> > -mario >> > >> > On Mon, Jan 25, 2021 at 3:56 AM Mario Kleiner <mario.kleiner.de@xxxxxxxxx> wrote: >> >> >> >> Hi Harry and Nicholas, >> >> >> >> I'm still on an extended quest to squeeze as much HDR out of Linux + your hw as possible, although the paid contract with Vesa has officially ended by now, and stumbled over this little conundrum: >> >> >> >> DC's set_spatial_dither() function (see link below) has this particular comment: >> >> "/* no 10bpc on DCE11*/" followed by code that skips dithering setup if the target output depth is 10 bpc: >> >> >> >> https://elixir.bootlin.com/linux/v5.11-rc4/source/drivers/gpu/drm/amd/display/dc/dce/dce_opp.c#L219 >> >> >> >> I couldn't find any hint in the commit messages towards the reason, so why is that? >> >> >> >> This gets in the way if one has a HDR-10 monitor with 10 bit native output depth connected and wants to output a fp16 framebuffer and retain some of the > 10 bit linear precision by use of spatial dithering down to 10 bit. One only gets the same precision as a 10 bpc unorm fb. Also the routine is called for all DCE's, not only DCE11, so it affects all of them. >> >> >> >> The same restrictions don't exist in the old kms code for amdgpu-kms and radeon-kms. I added a mmio hack to Psychtoolbox to go behind the drivers back and hack the FMT_BIT_DEPTH_CONTROL register to use spatial dithering down to 10 bpc anyway to circumvent this limitation. My photometer measurements on fp16 framebuffers feeding into 10 bit output show that I get a nice looking response consistent with dithering to 10 bpc properly working on DCE. Also i don't see any visual artifacts in displayed pictures, so the hw seems to be just fine. This on DCE-11.2, and more lightly tested on DCE-8.3. >> >> >> >> So i wonder if this is some leftover from some hw bringup, or if there is a good reason for it being there? Maybe it could be removed or made more specific to some problematic asic? >> >> >> >> Thanks for any insights you could provide. Stay safe, >> >> -mario >> >> >> > _______________________________________________ >> > amd-gfx mailing list >> > amd-gfx@xxxxxxxxxxxxxxxxxxxxx >> > https://lists.freedesktop.org/mailman/listinfo/amd-gfx _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
