[PATCH 04/11] drm/i915/dp_mst: Account for channel coding efficiency in the DSC DPT bpp limit

[Imre Deak]

The DSC DPT interface BW limit check should take into account the link
clock's (aka DDI clock in bspec) channel coding efficiency overhead.
Bspec doesn't mention this, however this matches how the link BW limit
is checked (that is the BW limit on wire as opposed to the above DPT
limit) for which Bspec doesn't mention the overhead either.

This fixes the DPT bpp limit for at least the 5k at 60Hz/DSC mode on a Dell
UHBR monitor/link I tested.

Bspec: 49259

Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index c21fd7a2cd44f..79f34be5c89da 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -59,11 +59,14 @@ static int intel_dp_mst_check_constraints(struct drm_i915_private *i915, int bpp
 	if (intel_dp_is_uhbr(crtc_state) && DISPLAY_VER(i915) < 14 && dsc) {
 		int output_bpp = bpp;
 		int symbol_clock = intel_dp_link_symbol_clock(crtc_state->port_clock);
+		int available_bw = mul_u32_u32(symbol_clock * 72,
+					       drm_dp_bw_channel_coding_efficiency(true)) /
+				   1000000;
 
 		if (output_bpp * adjusted_mode->crtc_clock >
-		    symbol_clock * 72) {
+		    available_bw) {
 			drm_dbg_kms(&i915->drm, "UHBR check failed(required bw %d available %d)\n",
-				    output_bpp * adjusted_mode->crtc_clock, symbol_clock * 72);
+				    output_bpp * adjusted_mode->crtc_clock, available_bw);
 			return -EINVAL;
 		}
 	}
-- 
2.43.3