[PATCH 2/3] drm/amd/display: Wait up to 1 s for slow sinks in FRL link training

[Andrzej Piątyszek]

LTS:3 gives the sink 220 ms (320 ms at 16 Gbps and above) to answer an
LTP request before the driver gives up on the rate. A Samsung QE65Q80T
(2020) sometimes answers at 10 Gbps x 4 only after 225 to 967 ms, so
link verification falls back to 6 Gbps x 3.

Wait up to 1 s at every rate. Sinks that answer within the old limit
are unaffected; a sink that never answers costs up to 1 s per rate in
the polling loop instead of 220 ms.

Fixes: cbb8e2044b9e ("drm/amd/display: Add DC link support for FRL")
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Andrzej Piątyszek <andrzej.piatyszek@xxxxxxxxx>
---
 .../drm/amd/display/dc/link/protocols/link_hdmi_frl.c    | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c
index 78e62bfec..97b2b9b74 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_hdmi_frl.c
@@ -612,10 +612,13 @@ static enum link_result hdmi_frl_perform_link_training(struct ddc_service *ddc_s
 
 		FRL_INFO("FRL LINK TRAINING:  Poll for FLT_UPDATE.\n");
 		/*LTS:3: Start Link Training*/
-		/*Start FLT Timer = 200 ms, or 300ms if link rate >= 16Gbps*/
+		/*
+		 * Start FLT Timer. Some sinks need longer than the nominal 200 ms
+		 * (300 ms at 16 Gbps and above) to answer an LTP request, so wait
+		 * up to 1 s before giving up on this rate.
+		 */
 		num_polls = 0;
-		if (link_settings->frl_link_rate >= HDMI_FRL_LINK_RATE_16GBPS)
-			poll_timeout_ns = 320 * 1000 * 1000;
+		poll_timeout_ns = 1000 * 1000 * 1000;
 
 		flt_poll_start = dm_get_timestamp(ddc_service->ctx);
 		uint8_t prev_flt_update = 0;
-- 
2.56.0