On 9/12/2022 11:39 AM, Dmitry Baryshkov wrote:
On 12/09/2022 19:23, Kuogee Hsieh wrote:
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
Fixes: 154b5a7da0fd ("drm/msm/dp: add displayPort driver support")
Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
---
drivers/gpu/drm/msm/dp/dp_ctrl.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c
b/drivers/gpu/drm/msm/dp/dp_ctrl.c
index ab6aa13..2c74c59 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;
It would be simpler to call drm_dp_dpcd_write(ssc, DP_DOWNSPREAD_CTRL,
1) unconditionally here. You won't have to change the
encoding/DP_MAIN_LINK_CHANNEL_CODING_SET/etc.
The difference is one write with 2 bytes against two writes with one
byte each.
I think it is more efficient to combine two bytes into one write since
these two bytes are consecutive address.
- 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;
