[PATCH 0/3] drm/amd/display: HDMI FRL training fixes for slow sinks

["Andrzej Piątyszek" <andrzej.piatyszek@gmail.com>]

With FRL on by default since commit 5fd3b60d9b80 ("drm/amd/display:
Enable HDMI FRL by default"), an RX 9070 XT mostly trains a Samsung
QE65Q80T (2020) at 6 Gbps x 3, where 4K 120 Hz needs DSC. Windows on
the same machine trains it at 10 Gbps x 4.

The TV needs one TxFFE step at 10 Gbps x 4, but requested levels never
reach the PHY; with patch 1, the driver programs them right away. The
TV sometimes answers an LTP request only after up to 967 ms, while the
driver waits only 220 ms in LTS:3; patch 2 raises the limit to 1 s.
After waking up, the TV can stay silent at 10 Gbps x 4 for up to about
four seconds, but link verification gives up on that rate after one
attempt; with patch 3, verification tries the same rate again first, as
the enable path does.

Tested on 7.3 with an equivalent backport. Without the series, 4 of 6
boots and TV wake-ups ended at 6 Gbps x 3. With patches 1 and 2, 16 of
20 reached 10 Gbps x 4, and the other 4 are the case patch 3 handles.
With all three, all 63 boots and TV wake-ups over 12 days reached
10 Gbps x 4. In 13 of them the sink stayed silent at first during link
verification and answered after one to three more attempts at the same
rate. On amd-staging-drm-next the series is build-tested only.

Andrzej Piątyszek (3):
  drm/amd/display: Apply requested TxFFE level right away in FRL
    training
  drm/amd/display: Wait up to 1 s for slow sinks in FRL link training
  drm/amd/display: Retry the same FRL rate after a sink timeout

 .../display/dc/link/protocols/link_hdmi_frl.c | 56 +++++++++++--------
 1 file changed, 33 insertions(+), 23 deletions(-)


base-commit: 47df73aa49d1988c8f684b7caf8be6570e966844
-- 
2.56.0