drm/i915/fdi: Recompute state for affected CRTCs on FDI links

Recompute the state of all CRTCs on an FDI link during a modeset that
may be affected by the modeset of other CRTCs on the same link. This
ensures that each CRTC on the link maximizes its BW use (after another
CRTC is disabled).

In practice this means recomputing pipe B's config on IVB if pipe C gets
disabled.

v2:
- Add the change recomputing affected CRTC states in a separate patch.
  (Ville)
v3: (Ville)
- Constify old and new crtc states.
- Check for fused off pipe C.
- Fix new vs. old crtc state mixup.
- Drop check for pipe C's enabled state.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230921195159.2646027-12-imre.deak@intel.com

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

@@ -6298,6 +6298,10 @@ static int intel_atomic_check_config(struct intel_atomic_state *state,
 	if (ret)
 		return ret;
 
+	ret = intel_fdi_add_affected_crtcs(state);
+	if (ret)
+		return ret;
+
 	for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i) {
 		if (!intel_crtc_needs_modeset(new_crtc_state)) {
 			if (intel_crtc_is_bigjoiner_slave(new_crtc_state))

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

@@ -120,6 +120,53 @@ void intel_fdi_link_train(struct intel_crtc *crtc,
 	dev_priv->display.funcs.fdi->fdi_link_train(crtc, crtc_state);
 }
 
+/**
+ * intel_fdi_add_affected_crtcs - add CRTCs on FDI affected by other modeset CRTCs
+ * @state: intel atomic state
+ *
+ * Add a CRTC using FDI to @state if changing another CRTC's FDI BW usage is
+ * known to affect the available FDI BW for the former CRTC. In practice this
+ * means adding CRTC B on IVYBRIDGE if its use of FDI lanes is limited (by
+ * CRTC C) and CRTC C is getting disabled.
+ *
+ * Returns 0 in case of success, or a negative error code otherwise.
+ */
+int intel_fdi_add_affected_crtcs(struct intel_atomic_state *state)
+{
+	struct drm_i915_private *i915 = to_i915(state->base.dev);
+	const struct intel_crtc_state *old_crtc_state;
+	const struct intel_crtc_state *new_crtc_state;
+	struct intel_crtc *crtc;
+
+	if (!IS_IVYBRIDGE(i915) || INTEL_NUM_PIPES(i915) != 3)
+		return 0;
+
+	crtc = intel_crtc_for_pipe(i915, PIPE_C);
+	new_crtc_state = intel_atomic_get_new_crtc_state(state, crtc);
+	if (!new_crtc_state)
+		return 0;
+
+	if (!intel_crtc_needs_modeset(new_crtc_state))
+		return 0;
+
+	old_crtc_state = intel_atomic_get_old_crtc_state(state, crtc);
+	if (!old_crtc_state->fdi_lanes)
+		return 0;
+
+	crtc = intel_crtc_for_pipe(i915, PIPE_B);
+	new_crtc_state = intel_atomic_get_crtc_state(&state->base, crtc);
+	if (IS_ERR(new_crtc_state))
+		return PTR_ERR(new_crtc_state);
+
+	old_crtc_state = intel_atomic_get_old_crtc_state(state, crtc);
+	if (!old_crtc_state->fdi_lanes)
+		return 0;
+
+	return intel_modeset_pipes_in_mask_early(state,
+						 "FDI link BW decrease on pipe C",
+						 BIT(PIPE_B));
+}
+
 /* units of 100MHz */
 static int pipe_required_fdi_lanes(struct intel_crtc_state *crtc_state)
 {

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

@@ -16,6 +16,7 @@ struct intel_crtc_state;
 struct intel_encoder;
 struct intel_link_bw_limits;
 
+int intel_fdi_add_affected_crtcs(struct intel_atomic_state *state);
 int intel_fdi_link_freq(struct drm_i915_private *i915,
 			const struct intel_crtc_state *pipe_config);
 bool intel_fdi_compute_pipe_bpp(struct intel_crtc_state *crtc_state);