UPSTREAM: drm/msm/dp: force link training for display resolution change

Display resolution change is implemented through drm modeset. Older
modeset (resolution) has to be disabled first before newer modeset
(resolution) can be enabled. Display disable will turn off both
pixel clock and main link clock so that main link have to be
re-trained during display enable to have new video stream flow
again. At current implementation, display enable function manually
kicks up irq_hpd_handle which will read panel link status and start
link training if link status is not in sync state.

However, there is rare case that a particular panel links status keep
staying in sync for some period of time after main link had been shut
down previously at display disabled. In this case, main link retraining
will not be executed by irq_hdp_handle(). Hence video stream of newer
display resolution will fail to be transmitted to panel due to main
link is not in sync between host and panel.

This patch will bypass irq_hpd_handle() in favor of directly call
dp_ctrl_on_stream() to always perform link training in regardless of
main link status. So that no unexpected exception resolution change
failure cases will happen. Also this implementation are more efficient
than manual kicking off irq_hpd_handle function.

Changes in v2:
-- set force_link_train flag on DP only (is_edp == false)

Changes in v3:
-- revise commit  text
-- add Fixes tag

Changes in v4:
-- revise commit  text

Changes in v5:
-- fix spelling at commit text

Changes in v6:
-- split dp_ctrl_on_stream() for phy test case
-- revise commit text for modeset

Changes in v7:
-- drop 0 assignment at local variable (ret = 0)

Changes in v8:
-- add patch to remove pixel_rate from dp_ctrl

Changes in v9:
-- forward declare dp_ctrl_on_stream_phy_test_report()

Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
Signed-off-by: Kuogee Hsieh <>
Reviewed-by: Stephen Boyd <>
Signed-off-by: Rob Clark <>
(cherry picked from commit a6e2af64a79afa7f1b29375b5231e840a84bb845)

TEST=emerge-trogdor chromeos-kernel-5_4; Switch DP to 640x480 and then back
     to higher resolution and see it work

Signed-off-by: Stephen Boyd <>
Change-Id: If3d0fac2af6c41ca446a018fb29112f9e3d4bfe5
Commit-Queue: Douglas Anderson <>
Reviewed-by: St├ęphane Marchesin <>
Reviewed-by: Douglas Anderson <>
Reviewed-by: Sean Paul <>
3 files changed