[PATCH] drm/dp: follow DP link CTS spec to read link status back

[Lee Shawn C <shawn.c.lee@intel.com>]

Refer to DP link CTS 1.2/1.4 spec, the following test case request
source read DPCD 200h - 205h to get latest link status from sink.

(4.3.2.4) Handling of IRQ HPD Pulse with No Error Status Bits Set
(400.3.2.1) Successful Link Re-training After IRQ HPD Pulse
            Due to Loss of Symbol Lock: HBR2 Extension
(400.3.2.2) Successful Link Re-training After IRQ HPD Pulse Due
            to Loss of Clock Recovery Lock: HBR2 Extension
(400.3.2.3) Successful Link Re-training After IRQ HPD Pulse Due
            to Loss of Inter-lane Alignment Lock: HBR2 Extension

So far, DRM DP driver just read back the link status from 202h
to 207h. DPR-120 would judge source can't pass these cases and
shows below error messages.

"Test FAILED, Source DUT does not read DPCD registers 200h-205h
within 100 ms".

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Cooper Chiou <cooper.chiou@intel.com>
Cc: William Tseng <william.tseng@intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 24bbc710c825..2b4d1f498ce3 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -410,17 +410,19 @@ int drm_dp_dpcd_read_phy_link_status(struct drm_dp_aux *aux,
 				     u8 link_status[DP_LINK_STATUS_SIZE])
 {
 	int ret;
+	u8 full_link_stat[DP_LINK_STATUS_SIZE + 2];
 
 	if (dp_phy == DP_PHY_DPRX) {
 		ret = drm_dp_dpcd_read(aux,
-				       DP_LANE0_1_STATUS,
-				       link_status,
-				       DP_LINK_STATUS_SIZE);
+				       DP_SINK_COUNT,
+				       full_link_stat,
+				       DP_LINK_STATUS_SIZE + 2);
 
 		if (ret < 0)
 			return ret;
 
-		WARN_ON(ret != DP_LINK_STATUS_SIZE);
+		memcpy(link_status, full_link_stat + 2, DP_LINK_STATUS_SIZE);
+		WARN_ON(ret != DP_LINK_STATUS_SIZE + 2);
 
 		return 0;
 	}
-- 
2.17.1