drm/radeon: fix DP link training issue with second 4K monitor

[ Upstream commit 1a738347df2ee4977459a8776fe2c62196bdcb1b ]

There is an issue observed when we hotplug a second DP
4K monitor to the system. Sometimes, the link training
fails for the second monitor after HPD interrupt
generation.

The issue happens when some queued or deferred transactions
are already present on the AUX channel when we initiate
a new transcation to (say) get DPCD or during link training.

We set AUX_IGNORE_HPD_DISCON bit in the AUX_CONTROL
register so that we can ignore any such deferred
transactions when a new AUX transaction is initiated.

Signed-off-by: Arindam Nath <arindam.nath@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

diff --git a/drivers/gpu/drm/radeon/radeon_dp_auxch.c b/drivers/gpu/drm/radeon/radeon_dp_auxch.c
index 3b0c229..db64e00 100644 (file)
--- a/drivers/gpu/drm/radeon/radeon_dp_auxch.c
+++ b/drivers/gpu/drm/radeon/radeon_dp_auxch.c
@@ -105,7 +105,7 @@ radeon_dp_aux_transfer_native(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg
 
        tmp &= AUX_HPD_SEL(0x7);
        tmp |= AUX_HPD_SEL(chan->rec.hpd);
-       tmp |= AUX_EN | AUX_LS_READ_EN;
+       tmp |= AUX_EN | AUX_LS_READ_EN | AUX_HPD_DISCON(0x1);
 
        WREG32(AUX_CONTROL + aux_offset[instance], tmp);