drm/amd/display: Read max down spread

[Why]
When launch D10.2, driver will write DPCD 0x107 with 0x00

[How]
Read MAX_DOWNSPREAD (0x0003h) then keep in current
link settings

Signed-off-by: Derek Lai <Derek.Lai@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index 07533cc..d685cde 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -532,6 +532,7 @@ static void read_edp_current_link_settings_on_detect(struct dc_link *link)
        uint32_t read_dpcd_retry_cnt = 10;
        enum dc_status status = DC_ERROR_UNEXPECTED;
        int i;
+       union max_down_spread max_down_spread = { {0} };
 
        // Read DPCD 00101h to find out the number of lanes currently set
        for (i = 0; i < read_dpcd_retry_cnt; i++) {
@@ -576,6 +577,12 @@ static void read_edp_current_link_settings_on_detect(struct dc_link *link)
                link->cur_link_settings.link_rate = link_bw_set;
                link->cur_link_settings.use_link_rate_set = false;
        }
+       // Read DPCD 00003h to find the max down spread.
+       core_link_read_dpcd(link, DP_MAX_DOWNSPREAD,
+                       &max_down_spread.raw, sizeof(max_down_spread));
+       link->cur_link_settings.link_spread =
+               max_down_spread.bits.MAX_DOWN_SPREAD ?
+               LINK_SPREAD_05_DOWNSPREAD_30KHZ : LINK_SPREAD_DISABLED;
 }
 
 static bool detect_dp(