drm/i915: Readout conn_state->max_bpc

Populate conn_state->max_bpc with something sensible from the start.
Otherwise it's possible that we get to compute_sink_pipe_bpp() with
max_bpc==0.

The specific scenario goes as follows:
1. Initial connector state allocated with max_bpc==0
2. Trigger a modeset on the crtc feeding the connector, without
   actually adding the connector to the commit
3. drm_atomic_connector_check() is skipped because the
   connector has not yet been added, hence conn_state->max_bpc
   retains its current value
4. drm_atomic_helper_check_modeset() ->
   drm_atomic_add_affected_connectors() -> the connector
   is now part of the commit
5. compute_baseline_pipe_bpp() -> MISSING_CASE(max_bpc==0)

Note that pipe_bpp itself may not be populated on pre-g4x machines,
in which case we just fall back to max_bpc==8 and let .compute_config()
limit the resulting pipe_bpp further if necessary.

Cc: Daniel Vetter <daniel@ffwll.ch>
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210216160035.4780-1-ville.syrjala@linux.intel.com
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index e106007..d7151a9 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -7991,19 +7991,27 @@ static void intel_modeset_update_connector_atomic_state(struct drm_device *dev)
 
        drm_connector_list_iter_begin(dev, &conn_iter);
        for_each_intel_connector_iter(connector, &conn_iter) {
-               if (connector->base.state->crtc)
+               struct drm_connector_state *conn_state = connector->base.state;
+               struct intel_encoder *encoder =
+                       to_intel_encoder(connector->base.encoder);
+
+               if (conn_state->crtc)
                        drm_connector_put(&connector->base);
 
-               if (connector->base.encoder) {
-                       connector->base.state->best_encoder =
-                               connector->base.encoder;
-                       connector->base.state->crtc =
-                               connector->base.encoder->crtc;
+               if (encoder) {
+                       struct intel_crtc *crtc =
+                               to_intel_crtc(encoder->base.crtc);
+                       const struct intel_crtc_state *crtc_state =
+                               to_intel_crtc_state(crtc->base.state);
+
+                       conn_state->best_encoder = &encoder->base;
+                       conn_state->crtc = &crtc->base;
+                       conn_state->max_bpc = (crtc_state->pipe_bpp ?: 24) / 3;
 
                        drm_connector_get(&connector->base);
                } else {
-                       connector->base.state->best_encoder = NULL;
-                       connector->base.state->crtc = NULL;
+                       conn_state->best_encoder = NULL;
+                       conn_state->crtc = NULL;
                }
        }
        drm_connector_list_iter_end(&conn_iter);