drm/amd/display: Fix DSC force enable on SST

[why]
Previously when force enabling DSC on SST display we unknowingly
supressed lane count, which caused DSC to be enabled automatically.

[how]
By adding an additional flag to force enable DSC in dc_dsc.c DSC can
always be enabled with debugfs dsc_clock_en forced to 1

Cc: stable@vger.kernel.org
Signed-off-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -4646,6 +4646,9 @@ create_stream_for_sink(struct amdgpu_dm_connector *aconnector,
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
 		if (dsc_caps.is_dsc_supported) {
+			/* Set DSC policy according to dsc_clock_en */
+			dc_dsc_policy_set_enable_dsc_when_not_needed(aconnector->dsc_settings.dsc_clock_en);
+
 			if (dc_dsc_compute_config(aconnector->dc_link->ctx->dc->res_pool->dscs[0],
 						  &dsc_caps,
 						  aconnector->dc_link->ctx->dc->debug.dsc_min_slice_height_override,

drivers/gpu/drm/amd/display/dc/dc_dsc.h

@@ -51,6 +51,7 @@ struct dc_dsc_policy {
 	int min_slice_height; // Must not be less than 8
 	uint32_t max_target_bpp;
 	uint32_t min_target_bpp;
+	bool enable_dsc_when_not_needed;
 };
 
 bool dc_dsc_parse_dsc_dpcd(const struct dc *dc,
@@ -80,4 +81,6 @@ void dc_dsc_get_policy_for_timing(const struct dc_crtc_timing *timing,
 
 void dc_dsc_policy_set_max_target_bpp_limit(uint32_t limit);
 
+void dc_dsc_policy_set_enable_dsc_when_not_needed(bool enable);
+
 #endif

drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c

@@ -34,6 +34,9 @@
 /* default DSC policy target bitrate limit is 16bpp */
 static uint32_t dsc_policy_max_target_bpp_limit = 16;
 
+/* default DSC policy enables DSC only when needed */
+static bool dsc_policy_enable_dsc_when_not_needed;
+
 static uint32_t dc_dsc_bandwidth_in_kbps_from_timing(
 	const struct dc_crtc_timing *timing)
 {
@@ -360,7 +363,7 @@ static bool decide_dsc_target_bpp_x16(
 
 	get_dsc_bandwidth_range(policy->min_target_bpp, policy->max_target_bpp,
 			dsc_common_caps, timing, &range);
-	if (target_bandwidth_kbps >= range.stream_kbps) {
+	if (!policy->enable_dsc_when_not_needed && target_bandwidth_kbps >= range.stream_kbps) {
 		/* enough bandwidth without dsc */
 		*target_bpp_x16 = 0;
 		should_use_dsc = false;
@@ -961,9 +964,20 @@ void dc_dsc_get_policy_for_timing(const struct dc_crtc_timing *timing, struct dc
 	/* internal upper limit, default 16 bpp */
 	if (policy->max_target_bpp > dsc_policy_max_target_bpp_limit)
 		policy->max_target_bpp = dsc_policy_max_target_bpp_limit;
+
+	/* enable DSC when not needed, default false */
+	if (dsc_policy_enable_dsc_when_not_needed)
+		policy->enable_dsc_when_not_needed = dsc_policy_enable_dsc_when_not_needed;
+	else
+		policy->enable_dsc_when_not_needed = false;
 }
 
 void dc_dsc_policy_set_max_target_bpp_limit(uint32_t limit)
 {
 	dsc_policy_max_target_bpp_limit = limit;
 }
+
+void dc_dsc_policy_set_enable_dsc_when_not_needed(bool enable)
+{
+	dsc_policy_enable_dsc_when_not_needed = enable;
+}