drm/i915/fdi: Improve FDI BW sharing between pipe B and C

At the moment modesetting pipe C on IVB will fail if pipe B uses 4 FDI
lanes. Make the BW sharing more dynamic by trying to reduce pipe B's
link bpp in this case, until pipe B uses only up to 2 FDI lanes.

For this instead of the encoder compute config retry loop - which
reduced link bpp only for the encoder's pipe - reduce the maximum link
bpp for pipe B/C as required after all CRTC states are computed and
recompute the CRTC states with the new bpp limit.

Atm, all FDI encoder's compute config function returns an error if a BW
constrain prevents increasing the pipe bpp value. The corresponding
crtc_state->bw_constrained check can be replaced with checking
crtc_state->max_link_bpp_x16, add TODO comments for this. SDVO is an
exception where this case is only handled in the outer config retry
loop, failing the modeset with a WARN, add a FIXME comment to handle
this in the encoder code similarly to other encoders.

v2:
- Don't assume that a CRTC is already in the atomic state, while
  reducing its link bpp.
- Add DocBook description to intel_fdi_atomic_check_link().
v3:
- Enable BW management for FDI links in a separate patch. (Ville)
v4: (Ville)
- Fail the SDVO encoder config computation if it doesn't support the
  link bpp limit.
- Add TODO: comments about checking link_bpp_x16 instead of
  bw_constrained.
v5:
- Replace link bpp limit check with a FIXME: comment in
  intel_sdvo_compute_config(). (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[Amended commit message wrt. changes in v5]
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230921195159.2646027-11-imre.deak@intel.com

drivers/gpu/drm/i915/display/g4x_hdmi.c

@@ -16,6 +16,7 @@
 #include "intel_display_types.h"
 #include "intel_dp_aux.h"
 #include "intel_dpio_phy.h"
+#include "intel_fdi.h"
 #include "intel_fifo_underrun.h"
 #include "intel_hdmi.h"
 #include "intel_hotplug.h"
@@ -133,8 +134,11 @@ static int g4x_hdmi_compute_config(struct intel_encoder *encoder,
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
 	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
 
-	if (HAS_PCH_SPLIT(i915))
+	if (HAS_PCH_SPLIT(i915)) {
 		crtc_state->has_pch_encoder = true;
+		if (!intel_fdi_compute_pipe_bpp(crtc_state))
+			return -EINVAL;
+	}
 
 	if (IS_G4X(i915))
 		crtc_state->has_hdmi_sink = g4x_compute_has_hdmi_sink(state, crtc);

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

@@ -413,6 +413,9 @@ static int pch_crt_compute_config(struct intel_encoder *encoder,
 		return -EINVAL;
 
 	pipe_config->has_pch_encoder = true;
+	if (!intel_fdi_compute_pipe_bpp(pipe_config))
+		return -EINVAL;
+
 	pipe_config->output_format = INTEL_OUTPUT_FORMAT_RGB;
 
 	return 0;
@@ -435,10 +438,14 @@ static int hsw_crt_compute_config(struct intel_encoder *encoder,
 		return -EINVAL;
 
 	pipe_config->has_pch_encoder = true;
+	if (!intel_fdi_compute_pipe_bpp(pipe_config))
+		return -EINVAL;
+
 	pipe_config->output_format = INTEL_OUTPUT_FORMAT_RGB;
 
 	/* LPT FDI RX only supports 8bpc. */
 	if (HAS_PCH_LPT(dev_priv)) {
+		/* TODO: Check crtc_state->max_link_bpp_x16 instead of bw_constrained */
 		if (pipe_config->bw_constrained && pipe_config->pipe_bpp < 24) {
 			drm_dbg_kms(&dev_priv->drm,
 				    "LPT only supports 24bpp\n");

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

@@ -4655,7 +4655,6 @@ intel_modeset_pipe_config(struct intel_atomic_state *state,
 	struct drm_connector_state *connector_state;
 	int pipe_src_w, pipe_src_h;
 	int base_bpp, ret, i;
-	bool retry = true;
 
 	crtc_state->cpu_transcoder = (enum transcoder) crtc->pipe;
 
@@ -4685,6 +4684,7 @@ intel_modeset_pipe_config(struct intel_atomic_state *state,
 			    "[CRTC:%d:%s] Link bpp limited to " BPP_X16_FMT "\n",
 			    crtc->base.base.id, crtc->base.name,
 			    BPP_X16_ARGS(crtc_state->max_link_bpp_x16));
+		crtc_state->bw_constrained = true;
 	}
 
 	base_bpp = crtc_state->pipe_bpp;
@@ -4728,7 +4728,6 @@ intel_modeset_pipe_config(struct intel_atomic_state *state,
 			crtc_state->output_types |= BIT(encoder->type);
 	}
 
-encoder_retry:
 	/* Ensure the port clock defaults are reset when retrying. */
 	crtc_state->port_clock = 0;
 	crtc_state->pixel_multiplier = 1;
@@ -4768,17 +4767,6 @@ intel_modeset_pipe_config(struct intel_atomic_state *state,
 	ret = intel_crtc_compute_config(state, crtc);
 	if (ret == -EDEADLK)
 		return ret;
-	if (ret == -EAGAIN) {
-		if (drm_WARN(&i915->drm, !retry,
-			     "[CRTC:%d:%s] loop in pipe configuration computation\n",
-			     crtc->base.base.id, crtc->base.name))
-			return -EINVAL;
-
-		drm_dbg_kms(&i915->drm, "[CRTC:%d:%s] bw constrained, retrying\n",
-			    crtc->base.base.id, crtc->base.name);
-		retry = false;
-		goto encoder_retry;
-	}
 	if (ret < 0) {
 		drm_dbg_kms(&i915->drm, "[CRTC:%d:%s] config failure: %d\n",
 			    crtc->base.base.id, crtc->base.name, ret);

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

@@ -2219,7 +2219,8 @@ intel_dp_compute_config_link_bpp_limits(struct intel_dp *intel_dp,
 	const struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
 	int max_link_bpp_x16;
 
-	max_link_bpp_x16 = to_bpp_x16(limits->pipe.max_bpp);
+	max_link_bpp_x16 = min(crtc_state->max_link_bpp_x16,
+			       to_bpp_x16(limits->pipe.max_bpp));
 
 	if (!dsc) {
 		max_link_bpp_x16 = rounddown(max_link_bpp_x16, to_bpp_x16(2 * 3));

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

@@ -13,6 +13,7 @@
 #include "intel_display_types.h"
 #include "intel_fdi.h"
 #include "intel_fdi_regs.h"
+#include "intel_link_bw.h"
 
 struct intel_fdi_funcs {
 	void (*fdi_link_train)(struct intel_crtc *crtc,
@@ -129,13 +130,16 @@ static int pipe_required_fdi_lanes(struct intel_crtc_state *crtc_state)
 }
 
 static int ilk_check_fdi_lanes(struct drm_device *dev, enum pipe pipe,
-			       struct intel_crtc_state *pipe_config)
+			       struct intel_crtc_state *pipe_config,
+			       enum pipe *pipe_to_reduce)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct drm_atomic_state *state = pipe_config->uapi.state;
 	struct intel_crtc *other_crtc;
 	struct intel_crtc_state *other_crtc_state;
 
+	*pipe_to_reduce = pipe;
+
 	drm_dbg_kms(&dev_priv->drm,
 		    "checking fdi config on pipe %c, lanes %i\n",
 		    pipe_name(pipe), pipe_config->fdi_lanes);
@@ -198,6 +202,9 @@ static int ilk_check_fdi_lanes(struct drm_device *dev, enum pipe pipe,
 		if (pipe_required_fdi_lanes(other_crtc_state) > 2) {
 			drm_dbg_kms(&dev_priv->drm,
 				    "fdi link B uses too many lanes to enable link C\n");
+
+			*pipe_to_reduce = PIPE_B;
+
 			return -EINVAL;
 		}
 		return 0;
@@ -232,16 +239,42 @@ int intel_fdi_link_freq(struct drm_i915_private *i915,
 		return i915->display.fdi.pll_freq;
 }
 
+/**
+ * intel_fdi_compute_pipe_bpp - compute pipe bpp limited by max link bpp
+ * @crtc_state: the crtc state
+ *
+ * Compute the pipe bpp limited by the CRTC's maximum link bpp. Encoders can
+ * call this function during state computation in the simple case where the
+ * link bpp will always match the pipe bpp. This is the case for all non-DP
+ * encoders, while DP encoders will use a link bpp lower than pipe bpp in case
+ * of DSC compression.
+ *
+ * Returns %true in case of success, %false if pipe bpp would need to be
+ * reduced below its valid range.
+ */
+bool intel_fdi_compute_pipe_bpp(struct intel_crtc_state *crtc_state)
+{
+	int pipe_bpp = min(crtc_state->pipe_bpp,
+			   to_bpp_int(crtc_state->max_link_bpp_x16));
+
+	pipe_bpp = rounddown(pipe_bpp, 2 * 3);
+
+	if (pipe_bpp < 6 * 3)
+		return false;
+
+	crtc_state->pipe_bpp = pipe_bpp;
+
+	return true;
+}
+
 int ilk_fdi_compute_config(struct intel_crtc *crtc,
 			   struct intel_crtc_state *pipe_config)
 {
 	struct drm_device *dev = crtc->base.dev;
 	struct drm_i915_private *i915 = to_i915(dev);
 	const struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
-	int lane, link_bw, fdi_dotclock, ret;
-	bool needs_recompute = false;
+	int lane, link_bw, fdi_dotclock;
 
-retry:
 	/* FDI is a binary signal running at ~2.7GHz, encoding
 	 * each output octet as 10 bits. The actual frequency
 	 * is stored as a divider into a 100MHz clock, and the
@@ -261,25 +294,69 @@ int ilk_fdi_compute_config(struct intel_crtc *crtc,
 	intel_link_compute_m_n(pipe_config->pipe_bpp, lane, fdi_dotclock,
 			       link_bw, &pipe_config->fdi_m_n, false);
 
-	ret = ilk_check_fdi_lanes(dev, crtc->pipe, pipe_config);
-	if (ret == -EDEADLK)
+	return 0;
+}
+
+static int intel_fdi_atomic_check_bw(struct intel_atomic_state *state,
+				     struct intel_crtc *crtc,
+				     struct intel_crtc_state *pipe_config,
+				     struct intel_link_bw_limits *limits)
+{
+	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
+	enum pipe pipe_to_reduce;
+	int ret;
+
+	ret = ilk_check_fdi_lanes(&i915->drm, crtc->pipe, pipe_config,
+				  &pipe_to_reduce);
+	if (ret != -EINVAL)
 		return ret;
 
-	if (ret == -EINVAL && pipe_config->pipe_bpp > 6*3) {
-		pipe_config->pipe_bpp -= 2*3;
-		drm_dbg_kms(&i915->drm,
-			    "fdi link bw constraint, reducing pipe bpp to %i\n",
-			    pipe_config->pipe_bpp);
-		needs_recompute = true;
-		pipe_config->bw_constrained = true;
+	ret = intel_link_bw_reduce_bpp(state, limits,
+				       BIT(pipe_to_reduce),
+				       "FDI link BW");
 
-		goto retry;
-	}
+	return ret ? : -EAGAIN;
+}
 
-	if (needs_recompute)
-		return -EAGAIN;
+/**
+ * intel_fdi_atomic_check_link - check all modeset FDI link configuration
+ * @state: intel atomic state
+ * @limits: link BW limits
+ *
+ * Check the link configuration for all modeset FDI outputs. If the
+ * configuration is invalid @limits will be updated if possible to
+ * reduce the total BW, after which the configuration for all CRTCs in
+ * @state must be recomputed with the updated @limits.
+ *
+ * Returns:
+ *   - 0 if the confugration is valid
+ *   - %-EAGAIN, if the configuration is invalid and @limits got updated
+ *     with fallback values with which the configuration of all CRTCs
+ *     in @state must be recomputed
+ *   - Other negative error, if the configuration is invalid without a
+ *     fallback possibility, or the check failed for another reason
+ */
+int intel_fdi_atomic_check_link(struct intel_atomic_state *state,
+				struct intel_link_bw_limits *limits)
+{
+	struct intel_crtc *crtc;
+	struct intel_crtc_state *crtc_state;
+	int i;
+
+	for_each_new_intel_crtc_in_state(state, crtc, crtc_state, i) {
+		int ret;
+
+		if (!crtc_state->has_pch_encoder ||
+		    !intel_crtc_needs_modeset(crtc_state) ||
+		    !crtc_state->hw.enable)
+			continue;
 
-	return ret;
+		ret = intel_fdi_atomic_check_bw(state, crtc, crtc_state, limits);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 
 static void cpt_set_fdi_bc_bifurcation(struct drm_i915_private *dev_priv, bool enable)

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

@@ -6,16 +6,23 @@
 #ifndef _INTEL_FDI_H_
 #define _INTEL_FDI_H_
 
+#include <linux/types.h>
+
 enum pipe;
 struct drm_i915_private;
+struct intel_atomic_state;
 struct intel_crtc;
 struct intel_crtc_state;
 struct intel_encoder;
+struct intel_link_bw_limits;
 
 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);
 int ilk_fdi_compute_config(struct intel_crtc *intel_crtc,
 			   struct intel_crtc_state *pipe_config);
+int intel_fdi_atomic_check_link(struct intel_atomic_state *state,
+				struct intel_link_bw_limits *limits);
 void intel_fdi_normal_train(struct intel_crtc *crtc);
 void ilk_fdi_disable(struct intel_crtc *crtc);
 void ilk_fdi_pll_disable(struct intel_crtc *intel_crtc);

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

@@ -7,6 +7,7 @@
 
 #include "intel_atomic.h"
 #include "intel_display_types.h"
+#include "intel_fdi.h"
 #include "intel_link_bw.h"
 
 /**
@@ -139,7 +140,13 @@ intel_link_bw_set_bpp_limit_for_pipe(struct intel_atomic_state *state,
 static int check_all_link_config(struct intel_atomic_state *state,
 				 struct intel_link_bw_limits *limits)
 {
-	/* TODO: Check all shared display link configurations like FDI */
+	/* TODO: Check additional shared display link configurations like MST */
+	int ret;
+
+	ret = intel_fdi_atomic_check_link(state, limits);
+	if (ret)
+		return ret;
+
 	return 0;
 }
 

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

@@ -425,11 +425,18 @@ static int intel_lvds_compute_config(struct intel_encoder *encoder,
 		return -EINVAL;
 	}
 
+	if (HAS_PCH_SPLIT(i915)) {
+		crtc_state->has_pch_encoder = true;
+		if (!intel_fdi_compute_pipe_bpp(crtc_state))
+			return -EINVAL;
+	}
+
 	if (lvds_encoder->a3_power == LVDS_A3_POWER_UP)
 		lvds_bpp = 8*3;
 	else
 		lvds_bpp = 6*3;
 
+	/* TODO: Check crtc_state->max_link_bpp_x16 instead of bw_constrained */
 	if (lvds_bpp != crtc_state->pipe_bpp && !crtc_state->bw_constrained) {
 		drm_dbg_kms(&i915->drm,
 			    "forcing display bpp (was %d) to LVDS (%d)\n",
@@ -453,9 +460,6 @@ static int intel_lvds_compute_config(struct intel_encoder *encoder,
 	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		return -EINVAL;
 
-	if (HAS_PCH_SPLIT(i915))
-		crtc_state->has_pch_encoder = true;
-
 	ret = intel_panel_fitting(crtc_state, conn_state);
 	if (ret)
 		return ret;

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

@@ -44,6 +44,7 @@
 #include "intel_crtc.h"
 #include "intel_de.h"
 #include "intel_display_types.h"
+#include "intel_fdi.h"
 #include "intel_fifo_underrun.h"
 #include "intel_gmbus.h"
 #include "intel_hdmi.h"
@@ -1351,14 +1352,18 @@ static int intel_sdvo_compute_config(struct intel_encoder *encoder,
 	struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
 	struct drm_display_mode *mode = &pipe_config->hw.mode;
 
+	if (HAS_PCH_SPLIT(to_i915(encoder->base.dev))) {
+		pipe_config->has_pch_encoder = true;
+		if (!intel_fdi_compute_pipe_bpp(pipe_config))
+			return -EINVAL;
+	}
+
 	DRM_DEBUG_KMS("forcing bpc to 8 for SDVO\n");
+	/* FIXME: Don't increase pipe_bpp */
 	pipe_config->pipe_bpp = 8*3;
 	pipe_config->sink_format = INTEL_OUTPUT_FORMAT_RGB;
 	pipe_config->output_format = INTEL_OUTPUT_FORMAT_RGB;
 
-	if (HAS_PCH_SPLIT(to_i915(encoder->base.dev)))
-		pipe_config->has_pch_encoder = true;
-
 	/*
 	 * We need to construct preferred input timings based on our
 	 * output timings.  To do that, we have to set the output