path: root/drivers/gpu
diff options
authorMatt Atwood <>2018-11-29 14:00:58 -0800
committerManasi Navare <>2018-12-05 15:45:04 -0800
commita1d926527b79576615839db39e3a5c7a7845f31c (patch)
treeec7d8348a933ebb18e02f13c548573c1da9e66f9 /drivers/gpu
parent79960227d93b81496365c35f5df162216f94d8e4 (diff)
According to DP spec ( of DP 1.4) if EXTENDED_RECEIVER_CAPABILITY_FIELD_PRESENT is set the addresses in DPCD 02200h through 0220Fh shall contain the DPRX's true capability. These values will match 00000h through 0000Fh, except for DPCD_REV, MAX_LINK_RATE, DOWN_STREAM_PORT_PRESENT. Read from DPCD once for all 3 values as this is an expensive operation. Spec mentions that all of address space 02200h through 0220Fh should contain the right information however currently only 3 values can differ. There is no address space in the intel_dp->dpcd struct for addresses 02200h through 0220Fh, and since so much of the data is a identical, simply overwrite the values stored in 00000h through 0000Fh with the values that can be overwritten from addresses 02200h through 0220Fh. This patch helps with backward compatibility for devices pre DP1.3. v2: read only dpcd values which can be affected, remove incorrect check, split into drm include changes into separate patch, commit message, verbose debugging statements during overwrite. v3: white space fixes v4: make path dependent on DPCD revision > 1.2 v5: split into function, removed DPCD rev check v6: add debugging prints for early exit conditions v7 (From Manasi): * Memcpy, memcmp and debig logging based on sizeof(dpcd_ext) (Jani N) * Exit early (Jani N) v8 (From Manasi): * Get rid of superfluous debug prints (Jani N) * Print entire base DPCD before memcpy (Jani N) v9 (From Manasi): * Add uniform newlines (Rodrigo) Cc: Jani Nikula <> Cc: Ville Syrjala <> Signed-off-by: Matt Atwood <> Signed-off-by: Manasi Navare <> Tested-by: Manasi Navare <> Acked-by: Manasi Navare <> Reviewed-by: Rodrigo Vivi <> Link:
Diffstat (limited to 'drivers/gpu')
1 files changed, 38 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index fdd2cbc56fa3..de4219721cbc 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3991,6 +3991,42 @@ intel_dp_link_down(struct intel_encoder *encoder,
+static void
+intel_dp_extended_receiver_capabilities(struct intel_dp *intel_dp)
+ u8 dpcd_ext[6];
+ /*
+ * Prior to DP1.3 the bit represented by
+ * if it is set DP_DPCD_REV at 0000h could be at a value less than
+ * the true capability of the panel. The only way to check is to
+ * then compare 0000h and 2200h.
+ */
+ if (!(intel_dp->dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
+ return;
+ if (drm_dp_dpcd_read(&intel_dp->aux, DP_DP13_DPCD_REV,
+ &dpcd_ext, sizeof(dpcd_ext)) != sizeof(dpcd_ext)) {
+ DRM_ERROR("DPCD failed read at extended capabilities\n");
+ return;
+ }
+ if (intel_dp->dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
+ DRM_DEBUG_KMS("DPCD extended DPCD rev less than base DPCD rev\n");
+ return;
+ }
+ if (!memcmp(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext)))
+ return;
+ DRM_DEBUG_KMS("Base DPCD: %*ph\n",
+ (int)sizeof(intel_dp->dpcd), intel_dp->dpcd);
+ memcpy(intel_dp->dpcd, dpcd_ext, sizeof(dpcd_ext));
intel_dp_read_dpcd(struct intel_dp *intel_dp)
@@ -3998,6 +4034,8 @@ intel_dp_read_dpcd(struct intel_dp *intel_dp)
sizeof(intel_dp->dpcd)) < 0)
return false; /* aux transfer failed */
+ intel_dp_extended_receiver_capabilities(intel_dp);
DRM_DEBUG_KMS("DPCD: %*ph\n", (int) sizeof(intel_dp->dpcd), intel_dp->dpcd);
return intel_dp->dpcd[DP_DPCD_REV] != 0;