drm/i915/dp_mst: Handle error during DSC BW overhead/slice calculation

The MST branch device may not support the number of DSC slices a mode
requires, handle the error in this case.

Fixes: 4e0837a8d00a ("drm/i915/dp_mst: Account for FEC and DSC overhead during BW allocation")
Cc: stable@vger.kernel.org # v6.8+
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241009110135.1216498-1-imre.deak@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 4765bda..2822ae1 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -90,27 +90,19 @@ static int intel_dp_mst_max_dpt_bpp(const struct intel_crtc_state *crtc_state,
 
 static int intel_dp_mst_bw_overhead(const struct intel_crtc_state *crtc_state,
                                    const struct intel_connector *connector,
-                                   bool ssc, bool dsc, int bpp_x16)
+                                   bool ssc, int dsc_slice_count, int bpp_x16)
 {
        const struct drm_display_mode *adjusted_mode =
                &crtc_state->hw.adjusted_mode;
        unsigned long flags = DRM_DP_BW_OVERHEAD_MST;
-       int dsc_slice_count = 0;
        int overhead;
 
        flags |= intel_dp_is_uhbr(crtc_state) ? DRM_DP_BW_OVERHEAD_UHBR : 0;
        flags |= ssc ? DRM_DP_BW_OVERHEAD_SSC_REF_CLK : 0;
        flags |= crtc_state->fec_enable ? DRM_DP_BW_OVERHEAD_FEC : 0;
 
-       if (dsc) {
-               int num_joined_pipes = intel_crtc_num_joined_pipes(crtc_state);
-
+       if (dsc_slice_count)
                flags |= DRM_DP_BW_OVERHEAD_DSC;
-               dsc_slice_count = intel_dp_dsc_get_slice_count(connector,
-                                                              adjusted_mode->clock,
-                                                              adjusted_mode->hdisplay,
-                                                              num_joined_pipes);
-       }
 
        overhead = drm_dp_bw_overhead(crtc_state->lane_count,
                                      adjusted_mode->hdisplay,
@@ -156,6 +148,19 @@ static int intel_dp_mst_calc_pbn(int pixel_clock, int bpp_x16, int bw_overhead)
        return DIV_ROUND_UP(effective_data_rate * 64, 54 * 1000);
 }
 
+static int intel_dp_mst_dsc_get_slice_count(const struct intel_connector *connector,
+                                           const struct intel_crtc_state *crtc_state)
+{
+       const struct drm_display_mode *adjusted_mode =
+               &crtc_state->hw.adjusted_mode;
+       int num_joined_pipes = intel_crtc_num_joined_pipes(crtc_state);
+
+       return intel_dp_dsc_get_slice_count(connector,
+                                           adjusted_mode->clock,
+                                           adjusted_mode->hdisplay,
+                                           num_joined_pipes);
+}
+
 static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
                                                struct intel_crtc_state *crtc_state,
                                                int max_bpp,
@@ -175,6 +180,7 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
        const struct drm_display_mode *adjusted_mode =
                &crtc_state->hw.adjusted_mode;
        int bpp, slots = -EINVAL;
+       int dsc_slice_count = 0;
        int max_dpt_bpp;
        int ret = 0;
 
@@ -206,6 +212,15 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
        drm_dbg_kms(&i915->drm, "Looking for slots in range min bpp %d max bpp %d\n",
                    min_bpp, max_bpp);
 
+       if (dsc) {
+               dsc_slice_count = intel_dp_mst_dsc_get_slice_count(connector, crtc_state);
+               if (!dsc_slice_count) {
+                       drm_dbg_kms(&i915->drm, "Can't get valid DSC slice count\n");
+
+                       return -ENOSPC;
+               }
+       }
+
        for (bpp = max_bpp; bpp >= min_bpp; bpp -= step) {
                int local_bw_overhead;
                int remote_bw_overhead;
@@ -219,9 +234,9 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
                                               intel_dp_output_bpp(crtc_state->output_format, bpp));
 
                local_bw_overhead = intel_dp_mst_bw_overhead(crtc_state, connector,
-                                                            false, dsc, link_bpp_x16);
+                                                            false, dsc_slice_count, link_bpp_x16);
                remote_bw_overhead = intel_dp_mst_bw_overhead(crtc_state, connector,
-                                                             true, dsc, link_bpp_x16);
+                                                             true, dsc_slice_count, link_bpp_x16);
 
                intel_dp_mst_compute_m_n(crtc_state, connector,
                                         local_bw_overhead,