Patch "drm/msm/dp: cleared DP_DOWNSPREAD_CTRL register before start link training" has been added to the 6.0-stable tree

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This is a note to let you know that I've just added the patch titled

    drm/msm/dp: cleared DP_DOWNSPREAD_CTRL register before start link training

to the 6.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-msm-dp-cleared-dp_downspread_ctrl-register-befor.patch
and it can be found in the queue-6.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7886ef163f3542d5b49591cbb61765a95295caa4
Author: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
Date:   Mon Sep 12 09:23:48 2022 -0700

    drm/msm/dp: cleared DP_DOWNSPREAD_CTRL register before start link training
    
    [ Upstream commit 70445dee1b4cf44c9fecc580dfa08079011866f1 ]
    
    DOWNSPREAD_CTRL (0x107) shall be cleared to 0 upon power-on reset or an
    upstream device disconnect. This patch will enforce this rule by always
    cleared DOWNSPREAD_CTRL register to 0 before start link training. At rare
    case that DP MSA timing parameters may be mis-interpreted by the sink
    which causes audio sampling rate be calculated wrongly and cause audio
    did not work at sink if DOWNSPREAD_CTRL register is not cleared to 0.
    
    Changes in v2:
    1) fix spelling at commit text
    2) merge ssc variable into encoding[0]
    
    Changes in v3:
    -- correct spelling of DOWNSPREAD_CTRL
    -- replace err with len of ssize_t
    
    Changes in v4:
    -- split into 2 patches
    
    Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
    Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
    Fixes: c943b4948b58 ("drm/msm/dp: add displayPort driver support")
    Patchwork: https://patchwork.freedesktop.org/patch/502532/
    Link: https://lore.kernel.org/r/1662999830-13916-2-git-send-email-quic_khsieh@xxxxxxxxxxx
    Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
index 013ca02e17cb..3ac139a4bbe8 100644
--- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
+++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
@@ -1245,8 +1245,7 @@ static int dp_ctrl_link_train(struct dp_ctrl_private *ctrl,
 {
 	int ret = 0;
 	const u8 *dpcd = ctrl->panel->dpcd;
-	u8 encoding = DP_SET_ANSI_8B10B;
-	u8 ssc;
+	u8 encoding[] = { 0, DP_SET_ANSI_8B10B };
 	u8 assr;
 	struct dp_link_info link_info = {0};
 
@@ -1258,13 +1257,11 @@ static int dp_ctrl_link_train(struct dp_ctrl_private *ctrl,
 
 	dp_aux_link_configure(ctrl->aux, &link_info);
 
-	if (drm_dp_max_downspread(dpcd)) {
-		ssc = DP_SPREAD_AMP_0_5;
-		drm_dp_dpcd_write(ctrl->aux, DP_DOWNSPREAD_CTRL, &ssc, 1);
-	}
+	if (drm_dp_max_downspread(dpcd))
+		encoding[0] |= DP_SPREAD_AMP_0_5;
 
-	drm_dp_dpcd_write(ctrl->aux, DP_MAIN_LINK_CHANNEL_CODING_SET,
-				&encoding, 1);
+	/* config DOWNSPREAD_CTRL and MAIN_LINK_CHANNEL_CODING_SET */
+	drm_dp_dpcd_write(ctrl->aux, DP_DOWNSPREAD_CTRL, encoding, 2);
 
 	if (drm_dp_alternate_scrambler_reset_cap(dpcd)) {
 		assr = DP_ALTERNATE_SCRAMBLER_RESET_ENABLE;



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