[PATCH 35/87] drm/amd/display: Read max down spread

[sunpeng.li at amd.com]

From: Derek Lai <Derek.Lai at amd.com>

[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 at amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng at amd.com>
Acked-by: Leo Li <sunpeng.li at amd.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 7 +++++++
 1 file changed, 7 insertions(+)

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 1e051e953610..4b82b86f1e6a 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -530,6 +530,7 @@ 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++) {
@@ -574,6 +575,12 @@ 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(
-- 
2.22.0