On 2018-06-26 05:43 PM, Emil Velikov wrote: > Hi Jerry, > > On 25 June 2018 at 22:45, Zuo, Jerry <jerry....@amd.com> wrote: >> Hello all: >> >> >> >> We are working on an issue affecting 4K@60 HDMI display not to light up, but >> only showing up 4K@30 from: >> https://bugs.freedesktop.org/show_bug.cgi?id=106959 and others. >> >> >> >> Some displays (e.g., ASUS PA328) HDMI port shows YCbCr420 CEA extension >> block with 4K@60 supported. Such HDMI 4K@60 is not real HDMI 2.0, but still >> following HDMI 1.4 spec. with maximum TMDS clock of 300MHz instead of >> 600MHz. >> >> To get such 4K@60 supported, it needs to limit the bandwidth by reducing the >> color space to YCbCr420 only. We’ve already raised YCbCr420 only flag >> (attached patch) from kernel side to pass the mode validation, and expose it >> to user space. >> >> >> >> We think that one of the issues that causes this problem is due to >> usermode pruning the 4K@60 mode from the modelist (attached Xorg.0.log). It >> seems like when usermode receives all the modes, it doesn't take in account >> the 4K@60 YCbCr4:2:0 specific mode. In order to pass validation of being >> added to usermode modelist, its pixel clk needs to be divided by 2 so that >> it won't exceed TMDS max physical pixel clk (300MHz). That might explain the >> difference in modes between our usermode and modeset. >> >> >> >> Such YCbCr4:2:0 4K@60 special mode is marked in DRM by raising a flag >> (y420_vdb_modes) inside connector's display_info which can be seen in >> do_y420vdb_modes(). Usermode could rely on that flag to pick up such mode >> and halve the required pclk to prevent such mode getting pruned out. >> >> >> >> We were hoping for someone helps to look at it from usermode perspective. >> Thanks a lot. >> > Just some observations, while going through some coffee. Take them > with a pinch of salt. > > Currently the kernel edid parser (in drm core) handles the > EXT_VIDEO_DATA_BLOCK_420 extended block. > Additionally, the kernel allows such modes only as the (per connector) > ycbcr_420_allowed bool is set by the driver. > > Quick look shows that it's only enabled by i915 on gen10 && geminilake > hardware. > > At the same time, X does it's own fairly partial edid parsing and > doesn't handle any(?) extended blocks. > > One solution is to update the X parser, although it seems like a > endless game of cat and mouse. > IMHO a much better approach is to not use edid codepaths for KMS > drivers (where AMDGPU is one). > On those, the supported modes is advertised by the kernel module via > drmModeGetConnector.
We are getting the modes from the kernel; the issue is they are then pruned (presumably by xf86ProbeOutputModes => xf86ValidateModesClocks) due to violating the clock limits, as described by Jerry above. -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer _______________________________________________ xorg-devel@lists.x.org: X.Org development Archives: http://lists.x.org/archives/xorg-devel Info: https://lists.x.org/mailman/listinfo/xorg-devel
