[PATCH 2/3] drm/i915: Displayport compliance test 4.2.2.7 support

[Todd Previte <tprevite@gmail.com>]

Adds support for complying with the requirements for test 4.2.2.7 Branch
Device Detection upon HPD Plug Event in the Displayport Link CTS 1.2 Core
rev1.1. This test checks to see if the source device can properly detect
a downstream branch device connected to the attached sink. It does so by
advertising the presence of a downstream port through the DPCD. The sink
count and content protection readiness bits are saved in the intel_dp
struct.

Note that as of HDCP 1.3 Displayport amendment, the CP_READY bit (bit 6)
in the SINK_COUNT register (DPCD 0x200) is no longer used. This bit
is stored here for compatibility for pre-HDCP 1.3 devices.

V1:
- Fixed formatting errors
V2:
- Updated for versioning

Signed-off-by: Todd Previte <tprevite@gmail.com>
---
 drivers/gpu/drm/i915/intel_dp.c  | 12 +++++++++++-
 drivers/gpu/drm/i915/intel_drv.h |  4 ++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 14147d0..697857a 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3856,8 +3856,18 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 	intel_dp_print_rates(intel_dp);
 
 	if (!(intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
-	      DP_DWN_STRM_PORT_PRESENT))
+	      DP_DWN_STRM_PORT_PRESENT)) {
 		return true; /* native DP sink */
+	} else {
+		uint8_t dpcd_byte;
+		/* Read Sink Count - DP Link CTS 1.2a rev1.1 4.2.2.7 */
+		intel_dp_dpcd_read_wake(&intel_dp->aux, DP_SINK_COUNT,
+					&dpcd_byte, 1);
+		intel_dp->sink_count = DP_GET_SINK_COUNT(dpcd_byte);
+		intel_dp->cp_ready = (dpcd_byte & DP_SINK_CP_READY) >> 6;
+		DRM_DEBUG_KMS("Sink count: %d  CP: %02x\n",
+			      intel_dp->sink_count, intel_dp->cp_ready);
+	}
 
 	if (intel_dp->dpcd[DP_DPCD_REV] == 0x10)
 		return true; /* no per-port downstream info */
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 6c71be9..f9a935c 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -744,6 +744,10 @@ struct intel_dp {
 	unsigned long compliance_test_type;
 	unsigned long compliance_test_data;
 	bool compliance_test_active;
+
+	/* Branch device support */
+	uint8_t sink_count;
+	uint8_t cp_ready;
 };
 
 struct intel_digital_port {
-- 
1.9.1

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