[PATCH] drm/i915: Preserve value of fec_enable calculated before DSC compute config

[Chaitanya Kumar Borah]

Before DSC compute config, fec_enable value is set in other functions
(e.g. intel_dp_mst_find_vcpi_slots_for_bpp). We are ignoring the value by
OR'ing its value in DSC compute config. One unintended effect of this is
setting fec_enable in UHBR use-cases which is not needed for Intel
hardware. Therefore, change operator to AND.

While at it, add a comment explaining why we don't enable FEC in eDP v1.5.

Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 49a37b996530..3fbf9f33c3e4 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2298,7 +2298,12 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 		&pipe_config->hw.adjusted_mode;
 	int ret;
 
-	pipe_config->fec_enable = pipe_config->fec_enable ||
+	/*
+	 * Though eDP v1.5 supports FEC with DSC, unlike DP, it is optional.
+	 * Since, FEC is a bandwidth overhead, continue to not enable it for
+	 * eDP. Until, there is a good reason to do so.
+	 */
+	pipe_config->fec_enable = pipe_config->fec_enable &&
 		(!intel_dp_is_edp(intel_dp) &&
 		 intel_dp_supports_fec(intel_dp, connector, pipe_config));
 
-- 
2.25.1