drm/i915/dp_tunnel: Fix error handling when clearing stream BW in atomic state

Clearing the DP tunnel stream BW in the atomic state involves getting
the tunnel group state, which can fail. Handle the error accordingly.

This fixes at least one issue where drm_dp_tunnel_atomic_set_stream_bw()
failed to get the tunnel group state returning -EDEADLK, which wasn't
handled. This lead to the ctx->contended warn later in modeset_lock()
while taking a WW mutex for another object in the same atomic state, and
thus within the same already contended WW context.

Moving intel_crtc_state_alloc() later would avoid freeing saved_state on
the error path; this stable patch leaves that simplification for a
follow-up.

Cc: Uma Shankar <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Cc: <[email protected]> # v6.9+
Fixes: a4efae8 ("drm/i915/dp: Compute DP tunnel BW during encoder state computation")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7617
Reviewed-by: Michał Grzelak <[email protected]>
Reviewed-by: Uma Shankar <[email protected]>
Signed-off-by: Imre Deak <[email protected]>
Link: https://patch.msgid.link/[email protected]
(cherry picked from commit fb69d00)
Signed-off-by: Joonas Lahtinen <[email protected]>

Author: ideak

drivers/gpu/drm/i915/display/intel_display.c

@@ -4602,6 +4602,7 @@ intel_crtc_prepare_cleared_state(struct intel_atomic_state *state,
 	struct intel_crtc_state *crtc_state =
 		intel_atomic_get_new_crtc_state(state, crtc);
 	struct intel_crtc_state *saved_state;
+	int err;
 
 	saved_state = intel_crtc_state_alloc(crtc);
 	if (!saved_state)
@@ -4610,7 +4611,12 @@ intel_crtc_prepare_cleared_state(struct intel_atomic_state *state,
 	/* free the old crtc_state->hw members */
 	intel_crtc_free_hw_state(crtc_state);
 
-	intel_dp_tunnel_atomic_clear_stream_bw(state, crtc_state);
+	err = intel_dp_tunnel_atomic_clear_stream_bw(state, crtc_state);
+	if (err) {
+		kfree(saved_state);
+
+		return err;
+	}
 
 	/* FIXME: before the switch to atomic started, a new pipe_config was
 	 * kzalloc'd. Code that depends on any field being zero should be

drivers/gpu/drm/i915/display/intel_dp_tunnel.c

@@ -621,19 +621,27 @@ int intel_dp_tunnel_atomic_compute_stream_bw(struct intel_atomic_state *state,
  *
  * Clear any DP tunnel stream BW requirement set by
  * intel_dp_tunnel_atomic_compute_stream_bw().
+ *
+ * Returns 0 in case of success, a negative error code otherwise.
  */
-void intel_dp_tunnel_atomic_clear_stream_bw(struct intel_atomic_state *state,
-					    struct intel_crtc_state *crtc_state)
+int intel_dp_tunnel_atomic_clear_stream_bw(struct intel_atomic_state *state,
+					   struct intel_crtc_state *crtc_state)
 {
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+	int err;
 
 	if (!crtc_state->dp_tunnel_ref.tunnel)
-		return;
+		return 0;
+
+	err = drm_dp_tunnel_atomic_set_stream_bw(&state->base,
+						 crtc_state->dp_tunnel_ref.tunnel,
+						 crtc->pipe, 0);
+	if (err)
+		return err;
 
-	drm_dp_tunnel_atomic_set_stream_bw(&state->base,
-					   crtc_state->dp_tunnel_ref.tunnel,
-					   crtc->pipe, 0);
 	drm_dp_tunnel_ref_put(&crtc_state->dp_tunnel_ref);
+
+	return 0;
 }
 
 /**

drivers/gpu/drm/i915/display/intel_dp_tunnel.h

@@ -40,8 +40,8 @@ int intel_dp_tunnel_atomic_compute_stream_bw(struct intel_atomic_state *state,
 					     struct intel_dp *intel_dp,
 					     const struct intel_connector *connector,
 					     struct intel_crtc_state *crtc_state);
-void intel_dp_tunnel_atomic_clear_stream_bw(struct intel_atomic_state *state,
-					    struct intel_crtc_state *crtc_state);
+int intel_dp_tunnel_atomic_clear_stream_bw(struct intel_atomic_state *state,
+					   struct intel_crtc_state *crtc_state);
 
 int intel_dp_tunnel_atomic_add_state_for_crtc(struct intel_atomic_state *state,
 					      struct intel_crtc *crtc);
@@ -88,9 +88,12 @@ intel_dp_tunnel_atomic_compute_stream_bw(struct intel_atomic_state *state,
 	return 0;
 }
 
-static inline void
+static inline int
 intel_dp_tunnel_atomic_clear_stream_bw(struct intel_atomic_state *state,
-				       struct intel_crtc_state *crtc_state) {}
+				       struct intel_crtc_state *crtc_state)
+{
+	return 0;
+}
 
 static inline int
 intel_dp_tunnel_atomic_add_state_for_crtc(struct intel_atomic_state *state,