drm/amd/display: dsc mst 2 4K displays go dark with 2 lane HBR3

[Why]
call stack of amdgpu dsc mst pbn, slot num calculation is as below:
-compute_bpp_x16_from_target_bandwidth
-decide_dsc_target_bpp_x16
-setup_dsc_config
-dc_dsc_compute_bandwidth_range
-compute_mst_dsc_configs_for_link
-compute_mst_dsc_configs_for_state

from pbn -> dsc target bpp_x16

bpp_x16 is calulated by compute_bpp_x16_from_target_bandwidth.
Beside pixel clock and bpp, num_slices_h and bpp_increment_div
will also affect bpp_x16.

from dsc target bpp_x16 -> pbn

within dm_update_mst_vcpi_slots_for_dsc,
pbn = drm_dp_calc_pbn_mode(clock, bpp_x16, true);

drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc)
{
  return DIV_ROUND_UP_ULL(mul_u32_u32(clock * (bpp / 16), 64 * 1006),
            8 * 54 * 1000 * 1000);
}

bpp / 16 trunc digits after decimal point. This will cause calculation
delta. drm_dp_calc_pbn_mode does not have other informations,
like num_slices_h, bpp_increment_div. therefore, it does not do revese
calcuation properly from bpp_x16 to pbn.

pbn from drm_dp_calc_pbn_mode is less than pbn from
compute_mst_dsc_configs_for_state. This cause not enough mst slot
allocated to display. display could not visually light up.

[How]
pass pbn from compute_mst_dsc_configs_for_state to
dm_update_mst_vcpi_slots_for_dsc

Cc: stable@vger.kernel.org

Reviewed-by: Scott Foster <Scott.Foster@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Hersen Wu <hersenwu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 16 insertions, 6 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 14ba5eeb974f..deb8010efc69 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -6794,14 +6794,15 @@ const struct drm_encoder_helper_funcs amdgpu_dm_encoder_helper_funcs = {
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
 static int dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
-					    struct dc_state *dc_state)
+					    struct dc_state *dc_state,
+					    struct dsc_mst_fairness_vars *vars)
 {
 	struct dc_stream_state *stream = NULL;
 	struct drm_connector *connector;
 	struct drm_connector_state *new_con_state;
 	struct amdgpu_dm_connector *aconnector;
 	struct dm_connector_state *dm_conn_state;
-	int i, j, clock, bpp;
+	int i, j, clock;
 	int vcpi, pbn_div, pbn = 0;
 
 	for_each_new_connector_in_state(state, connector, new_con_state, i) {
@@ -6840,9 +6841,15 @@ static int dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
 		}
 
 		pbn_div = dm_mst_get_pbn_divider(stream->link);
-		bpp = stream->timing.dsc_cfg.bits_per_pixel;
 		clock = stream->timing.pix_clk_100hz / 10;
-		pbn = drm_dp_calc_pbn_mode(clock, bpp, true);
+		/* pbn is calculated by compute_mst_dsc_configs_for_state*/
+		for (j = 0; j < dc_state->stream_count; j++) {
+			if (vars[j].aconnector == aconnector) {
+				pbn = vars[j].pbn;
+				break;
+			}
+		}
+
 		vcpi = drm_dp_mst_atomic_enable_dsc(state,
 						    aconnector->port,
 						    pbn, pbn_div,
@@ -10247,6 +10254,9 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 	int ret, i;
 	bool lock_and_validation_needed = false;
 	struct dm_crtc_state *dm_old_crtc_state;
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+	struct dsc_mst_fairness_vars vars[MAX_PIPES];
+#endif
 
 	trace_amdgpu_dm_atomic_check_begin(state);
 
@@ -10477,10 +10487,10 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 			goto fail;
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
-		if (!compute_mst_dsc_configs_for_state(state, dm_state->context))
+		if (!compute_mst_dsc_configs_for_state(state, dm_state->context, vars))
 			goto fail;
 
-		ret = dm_update_mst_vcpi_slots_for_dsc(state, dm_state->context);
+		ret = dm_update_mst_vcpi_slots_for_dsc(state, dm_state->context, vars);
 		if (ret)
 			goto fail;
 #endif