There's at least two firmware versions on the CalDigit DP20-HDMI21 adapter, which is powered by the ParadeTech PS196G chip. The first version has a bug where it incorrectly neglects to set the DOWN_STREAM_PORT_PRESENT field in the DPCD:
$ sudo dpcd_reg read --offset=0x2205 --count=1 --device=0 0x2205: 00 $ sudo dpcd_reg read --offset=0x0005 --count=1 --device=0 0x0005: 00 The newer one fixes this, and with this patch correctly negotiates VRR. [~]$ sudo dpcd_reg read --offset=0x5 --count=1 --device=2 0x0005: 1d [~]$ sudo dpcd_reg read --offset=0x2205 --count=1 --device=2 0x2205: 1d So if you're using a Paradetech adapter and it doesn't negotiate VRR, check that it has a firmware that produces the correct DPCD. Signed-off-by: Charles Munger <[email protected]> --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c index 6c827e6703a0..f463495d1c87 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c @@ -1410,6 +1410,7 @@ bool dm_helpers_is_vrr_pcon_allowed(const struct dc_link *link, const struct drm case DP_BRANCH_DEVICE_ID_00E04C: case DP_BRANCH_DEVICE_ID_90CC24: case DP_BRANCH_DEVICE_ID_2B02F0: + case DP_BRANCH_DEVICE_ID_001CF8: return true; } -- 2.54.0
