drm/i915: Populate pipe dbuf slices more accurately during readout

During readout we cannot assume the planes are actually using the
slices they are supposed to use. The BIOS may have misprogrammed
things and put the planes onto the wrong dbuf slices. So let's
do the readout more carefully to make sure we really know which
dbuf slices are actually in use by the pipe at the time.

Cc: <stable@vger.kernel.org> # v5.14+
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220204141818.1900-2-ville.syrjala@linux.intel.comReviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -6663,6 +6663,7 @@ void skl_wm_get_hw_state(struct drm_i915_private *dev_priv)
 		enum pipe pipe = crtc->pipe;
 		unsigned int mbus_offset;
 		enum plane_id plane_id;
+		u8 slices;
 
 		skl_pipe_wm_get_hw_state(crtc, &crtc_state->wm.skl.optimal);
 		crtc_state->wm.skl.raw = crtc_state->wm.skl.optimal;
@@ -6682,20 +6683,22 @@ void skl_wm_get_hw_state(struct drm_i915_private *dev_priv)
 			skl_ddb_entry_union(&dbuf_state->ddb[pipe], ddb_uv);
 		}
 
-		dbuf_state->slices[pipe] =
-			skl_compute_dbuf_slices(crtc, dbuf_state->active_pipes,
-						dbuf_state->joined_mbus);
-
 		dbuf_state->weight[pipe] = intel_crtc_ddb_weight(crtc_state);
 
 		/*
 		 * Used for checking overlaps, so we need absolute
 		 * offsets instead of MBUS relative offsets.
 		 */
-		mbus_offset = mbus_ddb_offset(dev_priv, dbuf_state->slices[pipe]);
+		slices = skl_compute_dbuf_slices(crtc, dbuf_state->active_pipes,
+						 dbuf_state->joined_mbus);
+		mbus_offset = mbus_ddb_offset(dev_priv, slices);
 		crtc_state->wm.skl.ddb.start = mbus_offset + dbuf_state->ddb[pipe].start;
 		crtc_state->wm.skl.ddb.end = mbus_offset + dbuf_state->ddb[pipe].end;
 
+		/* The slices actually used by the planes on the pipe */
+		dbuf_state->slices[pipe] =
+			skl_ddb_dbuf_slice_mask(dev_priv, &crtc_state->wm.skl.ddb);
+
 		drm_dbg_kms(&dev_priv->drm,
 			    "[CRTC:%d:%s] dbuf slices 0x%x, ddb (%d - %d), active pipes 0x%x, mbus joined: %s\n",
 			    crtc->base.base.id, crtc->base.name,