[Intel-gfx] [PATCH v2] drm/i915: fix lane bandwidth capping for DP 1.2 sinks

[Imre Deak]

DP 1.2 compatible displays may report a 5.4Gbps maximum bandwidth which
the driver will treat as an invalid value and use 1.62Gbps instead. Fix
this by capping to 2.7Gbps for sinks reporting a 5.4Gbps max bw.

Also add a warning for reserved values.

v2:
- allow only bw values explicitly listed in the DP standard (Daniel,
  Chris)

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 11eb697..7db2cd7 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -75,7 +75,12 @@ intel_dp_max_link_bw(struct intel_dp *intel_dp)
 	case DP_LINK_BW_1_62:
 	case DP_LINK_BW_2_7:
 		break;
+	case DP_LINK_BW_5_4: /* 1.2 capable displays may advertise higher bw */
+		max_link_bw = DP_LINK_BW_2_7;
+		break;
 	default:
+		WARN(1, "invalid max DP link bw val %x, using 1.62Gbps\n",
+		     max_link_bw);
 		max_link_bw = DP_LINK_BW_1_62;
 		break;
 	}
-- 
1.8.1.2