Nouveau - Jun 2019 - [PATCH AUTOSEL 4.14 18/99] drm/nouveau/disp/dp: respect sink limits when selecting failsafe link configuration

From: Ben Skeggs <bskeggs at redhat.com>

[ Upstream commit 13d03e9daf70dab032c03dc172e75bb98ad899c4 ]

Where possible, we want the failsafe link configuration (one which won't
hang the OR during modeset because of not enough bandwidth for the mode)
to also be supported by the sink.

This prevents "link rate unsupported by sink" messages when link
training
fails.

Signed-off-by: Ben Skeggs <bskeggs at redhat.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
index 6160a6158cf26..5e51a5c1eb013 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
@@ -364,8 +364,15 @@ nvkm_dp_train(struct nvkm_dp *dp, u32 dataKBps)
 	 * and it's better to have a failed modeset than that.
 	 */
 	for (cfg = nvkm_dp_rates; cfg->rate; cfg++) {
-		if (cfg->nr <= outp_nr && cfg->nr <= outp_bw)
-			failsafe = cfg;
+		if (cfg->nr <= outp_nr && cfg->nr <= outp_bw) {
+			/* Try to respect sink limits too when selecting
+			 * lowest link configuration.
+			 */
+			if (!failsafe ||
+			    (cfg->nr <= sink_nr && cfg->bw <= sink_bw))
+				failsafe = cfg;
+		}
+
 		if (failsafe && cfg[1].rate < dataKBps)
 			break;
 	}
-- 
2.20.1