[v9,06/12] drm/bridge: Add the necessary bits to support bus format negotiation

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index afe14f72a824..ea1926b5bb80 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3528,3 +3528,44 @@  int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
 	return ret;
 }
 EXPORT_SYMBOL(drm_atomic_helper_legacy_gamma_set);
+
+/**
+ * drm_atomic_helper_bridge_propagate_bus_fmt() - Propagate output format to
+ *						  the input end of a bridge
+ * @bridge: bridge control structure
+ * @bridge_state: new bridge state
+ * @crtc_state: new CRTC state
+ * @conn_state: new connector state
+ * @output_fmt: tested output bus format
+ * @num_input_fmts: will contain the size of the returned array
+ *
+ * This helper is a pluggable implementation of the
+ * &drm_bridge_funcs.atomic_get_input_bus_fmts operation for bridges that don't
+ * modify the bus configuration between their input and their output. It
+ * returns an array of input formats with a single element set to @output_fmt.
+ *
+ * RETURNS:
+ * a valid format array of size @num_input_fmts, or NULL if the allocation
+ * failed
+ */
+u32 *
+drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
+					struct drm_bridge_state *bridge_state,
+					struct drm_crtc_state *crtc_state,
+					struct drm_connector_state *conn_state,
+					u32 output_fmt,
+					unsigned int *num_input_fmts)
+{
+	u32 *input_fmts;
+
+	input_fmts = kzalloc(sizeof(*input_fmts), GFP_KERNEL);
+	if (!input_fmts) {
+		*num_input_fmts = 0;
+		return NULL;
+	}
+
+	*num_input_fmts = 1;
+	input_fmts[0] = output_fmt;
+	return input_fmts;
+}
+EXPORT_SYMBOL(drm_atomic_helper_bridge_propagate_bus_fmt);
diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index c8beb1385771..68ab933ee430 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -628,13 +628,247 @@  static int drm_atomic_bridge_check(struct drm_bridge *bridge,
 	return 0;
 }
 
+static int select_bus_fmt_recursive(struct drm_bridge *first_bridge,
+				    struct drm_bridge *cur_bridge,
+				    struct drm_crtc_state *crtc_state,
+				    struct drm_connector_state *conn_state,
+				    u32 out_bus_fmt)
+{
+	struct drm_bridge_state *cur_state;
+	unsigned int num_in_bus_fmts, i;
+	struct drm_bridge *prev_bridge;
+	u32 *in_bus_fmts;
+	int ret;
+
+	prev_bridge = drm_bridge_get_prev_bridge(cur_bridge);
+	cur_state = drm_atomic_get_new_bridge_state(crtc_state->state,
+						    cur_bridge);
+
+	/*
+	 * If bus format negotiation is not supported by this bridge, let's
+	 * pass MEDIA_BUS_FMT_FIXED to the previous bridge in the chain and
+	 * hope that it can handle this situation gracefully (by providing
+	 * appropriate default values).
+	 */
+	if (!cur_bridge->funcs->atomic_get_input_bus_fmts) {
+		if (cur_bridge != first_bridge) {
+			ret = select_bus_fmt_recursive(first_bridge,
+						       prev_bridge, crtc_state,
+						       conn_state,
+						       MEDIA_BUS_FMT_FIXED);
+			if (ret)
+				return ret;
+		}
+
+		/*
+		 * Driver does not implement the atomic state hooks, but that's
+		 * fine, as long as it does not access the bridge state.
+		 */
+		if (cur_state) {
+			cur_state->input_bus_cfg.format = MEDIA_BUS_FMT_FIXED;
+			cur_state->output_bus_cfg.format = out_bus_fmt;
+		}
+
+		return 0;
+	}
+
+	/*
+	 * If the driver implements ->atomic_get_input_bus_fmts() it
+	 * should also implement the atomic state hooks.
+	 */
+	if (WARN_ON(!cur_state))
+		return -EINVAL;
+
+	in_bus_fmts = cur_bridge->funcs->atomic_get_input_bus_fmts(cur_bridge,
+							cur_state,
+							crtc_state,
+							conn_state,
+							out_bus_fmt,
+							&num_in_bus_fmts);
+	if (!num_in_bus_fmts)
+		return -ENOTSUPP;
+	else if (!in_bus_fmts)
+		return -ENOMEM;
+
+	if (first_bridge == cur_bridge) {
+		cur_state->input_bus_cfg.format = in_bus_fmts[0];
+		cur_state->output_bus_cfg.format = out_bus_fmt;
+		kfree(in_bus_fmts);
+		return 0;
+	}
+
+	for (i = 0; i < num_in_bus_fmts; i++) {
+		ret = select_bus_fmt_recursive(first_bridge, prev_bridge,
+					       crtc_state, conn_state,
+					       in_bus_fmts[i]);
+		if (ret != -ENOTSUPP)
+			break;
+	}
+
+	if (!ret) {
+		cur_state->input_bus_cfg.format = in_bus_fmts[i];
+		cur_state->output_bus_cfg.format = out_bus_fmt;
+	}
+
+	kfree(in_bus_fmts);
+	return ret;
+}
+
+/*
+ * This function is called by &drm_atomic_bridge_chain_check() just before
+ * calling &drm_bridge_funcs.atomic_check() on all elements of the chain.
+ * It performs bus format negotiation between bridge elements. The negotiation
+ * happens in reverse order, starting from the last element in the chain up to
+ * @bridge.
+ *
+ * Negotiation starts by retrieving supported output bus formats on the last
+ * bridge element and testing them one by one. The test is recursive, meaning
+ * that for each tested output format, the whole chain will be walked backward,
+ * and each element will have to choose an input bus format that can be
+ * transcoded to the requested output format. When a bridge element does not
+ * support transcoding into a specific output format -ENOTSUPP is returned and
+ * the next bridge element will have to try a different format. If none of the
+ * combinations worked, -ENOTSUPP is returned and the atomic modeset will fail.
+ *
+ * This implementation is relying on
+ * &drm_bridge_funcs.atomic_get_output_bus_fmts() and
+ * &drm_bridge_funcs.atomic_get_input_bus_fmts() to gather supported
+ * input/output formats.
+ *
+ * When &drm_bridge_funcs.atomic_get_output_bus_fmts() is not implemented by
+ * the last element of the chain, &drm_atomic_bridge_chain_select_bus_fmts()
+ * tries a single format: &drm_connector.display_info.bus_formats[0] if
+ * available, MEDIA_BUS_FMT_FIXED otherwise.
+ *
+ * When &drm_bridge_funcs.atomic_get_input_bus_fmts() is not implemented,
+ * &drm_atomic_bridge_chain_select_bus_fmts() skips the negotiation on the
+ * bridge element that lacks this hook and asks the previous element in the
+ * chain to try MEDIA_BUS_FMT_FIXED. It's up to bridge drivers to decide what
+ * to do in that case (fail if they want to enforce bus format negotiation, or
+ * provide a reasonable default if they need to support pipelines where not
+ * all elements support bus format negotiation).
+ */
+static int
+drm_atomic_bridge_chain_select_bus_fmts(struct drm_bridge *bridge,
+					struct drm_crtc_state *crtc_state,
+					struct drm_connector_state *conn_state)
+{
+	struct drm_connector *conn = conn_state->connector;
+	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_bridge_state *last_bridge_state;
+	unsigned int i, num_out_bus_fmts;
+	struct drm_bridge *last_bridge;
+	u32 *out_bus_fmts;
+	int ret = 0;
+
+	last_bridge = list_last_entry(&encoder->bridge_chain,
+				      struct drm_bridge, chain_node);
+	last_bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
+							    last_bridge);
+
+	if (last_bridge->funcs->atomic_get_output_bus_fmts) {
+		const struct drm_bridge_funcs *funcs = last_bridge->funcs;
+
+		/*
+		 * If the driver implements ->atomic_get_output_bus_fmts() it
+		 * should also implement the atomic state hooks.
+		 */
+		if (WARN_ON(!last_bridge_state))
+			return -EINVAL;
+
+		out_bus_fmts = funcs->atomic_get_output_bus_fmts(last_bridge,
+							last_bridge_state,
+							crtc_state,
+							conn_state,
+							&num_out_bus_fmts);
+		if (!num_out_bus_fmts)
+			return -ENOTSUPP;
+		else if (!out_bus_fmts)
+			return -ENOMEM;
+	} else {
+		num_out_bus_fmts = 1;
+		out_bus_fmts = kmalloc(sizeof(*out_bus_fmts), GFP_KERNEL);
+		if (!out_bus_fmts)
+			return -ENOMEM;
+
+		if (conn->display_info.num_bus_formats &&
+		    conn->display_info.bus_formats)
+			out_bus_fmts[0] = conn->display_info.bus_formats[0];
+		else
+			out_bus_fmts[0] = MEDIA_BUS_FMT_FIXED;
+	}
+
+	for (i = 0; i < num_out_bus_fmts; i++) {
+		ret = select_bus_fmt_recursive(bridge, last_bridge, crtc_state,
+					       conn_state, out_bus_fmts[i]);
+		if (ret != -ENOTSUPP)
+			break;
+	}
+
+	kfree(out_bus_fmts);
+
+	return ret;
+}
+
+static void
+drm_atomic_bridge_propagate_bus_flags(struct drm_bridge *bridge,
+				      struct drm_connector *conn,
+				      struct drm_atomic_state *state)
+{
+	struct drm_bridge_state *bridge_state, *next_bridge_state;
+	struct drm_bridge *next_bridge;
+	u32 output_flags = 0;
+
+	bridge_state = drm_atomic_get_new_bridge_state(state, bridge);
+
+	/* No bridge state attached to this bridge => nothing to propagate. */
+	if (!bridge_state)
+		return;
+
+	next_bridge = drm_bridge_get_next_bridge(bridge);
+
+	/*
+	 * Let's try to apply the most common case here, that is, propagate
+	 * display_info flags for the last bridge, and propagate the input
+	 * flags of the next bridge element to the output end of the current
+	 * bridge when the bridge is not the last one.
+	 * There are exceptions to this rule, like when signal inversion is
+	 * happening at the board level, but that's something drivers can deal
+	 * with from their &drm_bridge_funcs.atomic_check() implementation by
+	 * simply overriding the flags value we've set here.
+	 */
+	if (!next_bridge) {
+		output_flags = conn->display_info.bus_flags;
+	} else {
+		next_bridge_state = drm_atomic_get_new_bridge_state(state,
+								next_bridge);
+		/*
+		 * No bridge state attached to the next bridge, just leave the
+		 * flags to 0.
+		 */
+		if (next_bridge_state)
+			output_flags = next_bridge_state->input_bus_cfg.flags;
+	}
+
+	bridge_state->output_bus_cfg.flags = output_flags;
+
+	/*
+	 * Propage the output flags to the input end of the bridge. Again, it's
+	 * not necessarily what all bridges want, but that's what most of them
+	 * do, and by doing that by default we avoid forcing drivers to
+	 * duplicate the "dummy propagation" logic.
+	 */
+	bridge_state->input_bus_cfg.flags = output_flags;
+}
+
 /**
  * drm_atomic_bridge_chain_check() - Do an atomic check on the bridge chain
  * @bridge: bridge control structure
  * @crtc_state: new CRTC state
  * @conn_state: new connector state
  *
- * Calls &drm_bridge_funcs.atomic_check() (falls back on
+ * First trigger a bus format negotiation before calling
+ * &drm_bridge_funcs.atomic_check() (falls back on
  * &drm_bridge_funcs.mode_fixup()) op for all the bridges in the encoder chain,
  * starting from the last bridge to the first. These are called before calling
  * &drm_encoder_helper_funcs.atomic_check()
@@ -646,16 +880,33 @@  int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
 				  struct drm_crtc_state *crtc_state,
 				  struct drm_connector_state *conn_state)
 {
+	struct drm_connector *conn = conn_state->connector;
 	struct drm_encoder *encoder;
 	struct drm_bridge *iter;
+	int ret;
 
 	if (!bridge)
 		return 0;
 
+	ret = drm_atomic_bridge_chain_select_bus_fmts(bridge, crtc_state,
+						      conn_state);
+	if (ret)
+		return ret;
+
 	encoder = bridge->encoder;
 	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
 		int ret;
 
+		/*
+		 * Bus flags are propagated by default. If a bridge needs to
+		 * tweak the input bus flags for any reason, it should happen
+		 * in its &drm_bridge_funcs.atomic_check() implementation such
+		 * that preceding bridges in the chain can propagate the new
+		 * bus flags.
+		 */
+		drm_atomic_bridge_propagate_bus_flags(iter, conn,
+						      crtc_state->state);
+
 		ret = drm_atomic_bridge_check(iter, crtc_state, conn_state);
 		if (ret)
 			return ret;
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 82a888769b3d..52d65a055491 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -995,6 +995,38 @@  drm_atomic_crtc_effectively_active(const struct drm_crtc_state *state)
 	return state->active || state->self_refresh_active;
 }
 
+/**
+ * struct drm_bus_cfg - bus configuration
+ *
+ * This structure stores the configuration of a physical bus between two
+ * components in an output pipeline, usually between two bridges, an encoder
+ * and a bridge, or a bridge and a connector.
+ *
+ * The bus configuration is stored in &drm_bridge_state separately for the
+ * input and output buses, as seen from the point of view of each bridge. The
+ * bus configuration of a bridge output is usually identical to the
+ * configuration of the next bridge's input, but may differ if the signals are
+ * modified between the two bridges, for instance by an inverter on the board.
+ * The input and output configurations of a bridge may differ if the bridge
+ * modifies the signals internally, for instance by performing format
+ * conversion, or modifying signals polarities.
+ */
+struct drm_bus_cfg {
+	/**
+	 * @format: format used on this bus (one of the MEDIA_BUS_FMT_* format)
+	 *
+	 * This field should not be directly modified by drivers
+	 * (&drm_atomic_bridge_chain_select_bus_fmts() takes care of the bus
+	 * format negotiation).
+	 */
+	u32 format;
+
+	/**
+	 * @flags: DRM_BUS_* flags used on this bus
+	 */
+	u32 flags;
+};
+
 /**
  * struct drm_bridge_state - Atomic bridge state object
  */
@@ -1008,6 +1040,16 @@  struct drm_bridge_state {
 	 * @bridge: the bridge this state refers to
 	 */
 	struct drm_bridge *bridge;
+
+	/**
+	 * @input_bus_cfg: input bus configuration
+	 */
+	struct drm_bus_cfg input_bus_cfg;
+
+	/**
+	 * @output_bus_cfg: input bus configuration
+	 */
+	struct drm_bus_cfg output_bus_cfg;
 };
 
 static inline struct drm_bridge_state *
diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index 9db3cac48f4f..b268180c97eb 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -224,4 +224,12 @@  drm_atomic_plane_disabling(struct drm_plane_state *old_plane_state,
 	return old_plane_state->crtc && !new_plane_state->crtc;
 }
 
+u32 *
+drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
+					struct drm_bridge_state *bridge_state,
+					struct drm_crtc_state *crtc_state,
+					struct drm_connector_state *conn_state,
+					u32 output_fmt,
+					unsigned int *num_input_fmts);
+
 #endif /* DRM_ATOMIC_HELPER_H_ */
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index ff4df6eb2689..45626ecf20f8 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -370,6 +370,72 @@  struct drm_bridge_funcs {
 	void (*atomic_destroy_state)(struct drm_bridge *bridge,
 				     struct drm_bridge_state *state);
 
+	/**
+	 * @atomic_get_output_bus_fmts:
+	 *
+	 * Return the supported bus formats on the output end of a bridge.
+	 * The returned array must be allocated with kmalloc() and will be
+	 * freed by the caller. If the allocation fails, NULL should be
+	 * returned. num_output_fmts must be set to the returned array size.
+	 * Formats listed in the returned array should be listed in decreasing
+	 * preference order (the core will try all formats until it finds one
+	 * that works).
+	 *
+	 * This method is only called on the last element of the bridge chain
+	 * as part of the bus format negotiation process that happens in
+	 * &drm_atomic_bridge_chain_select_bus_fmts().
+	 * This method is optional. When not implemented, the core will
+	 * fall back to &drm_connector.display_info.bus_formats[0] if
+	 * &drm_connector.display_info.num_bus_formats > 0,
+	 * or to MEDIA_BUS_FMT_FIXED otherwise.
+	 */
+	u32 *(*atomic_get_output_bus_fmts)(struct drm_bridge *bridge,
+					   struct drm_bridge_state *bridge_state,
+					   struct drm_crtc_state *crtc_state,
+					   struct drm_connector_state *conn_state,
+					   unsigned int *num_output_fmts);
+
+	/**
+	 * @atomic_get_input_bus_fmts:
+	 *
+	 * Return the supported bus formats on the input end of a bridge for
+	 * a specific output bus format.
+	 *
+	 * The returned array must be allocated with kmalloc() and will be
+	 * freed by the caller. If the allocation fails, NULL should be
+	 * returned. num_output_fmts must be set to the returned array size.
+	 * Formats listed in the returned array should be listed in decreasing
+	 * preference order (the core will try all formats until it finds one
+	 * that works). When the format is not supported NULL should be
+	 * returned and *num_output_fmts should be set to 0.
+	 *
+	 * This method is called on all elements of the bridge chain as part of
+	 * the bus format negotiation process that happens in
+	 * &drm_atomic_bridge_chain_select_bus_fmts().
+	 * This method is optional. When not implemented, the core will bypass
+	 * bus format negotiation on this element of the bridge without
+	 * failing, and the previous element in the chain will be passed
+	 * MEDIA_BUS_FMT_FIXED as its output bus format.
+	 *
+	 * Bridge drivers that need to support being linked to bridges that are
+	 * not supporting bus format negotiation should handle the
+	 * output_fmt == MEDIA_BUS_FMT_FIXED case appropriately, by selecting a
+	 * sensible default value or extracting this information from somewhere
+	 * else (FW property, &drm_display_mode, &drm_display_info, ...)
+	 *
+	 * Note: Even if input format selection on the first bridge has no
+	 * impact on the negotiation process (bus format negotiation stops once
+	 * we reach the first element of the chain), drivers are expected to
+	 * return accurate input formats as the input format may be used to
+	 * configure the CRTC output appropriately.
+	 */
+	u32 *(*atomic_get_input_bus_fmts)(struct drm_bridge *bridge,
+					  struct drm_bridge_state *bridge_state,
+					  struct drm_crtc_state *crtc_state,
+					  struct drm_connector_state *conn_state,
+					  u32 output_fmt,
+					  unsigned int *num_input_fmts);
+
 	/**
 	 * @atomic_check:
 	 *
@@ -384,6 +450,14 @@  struct drm_bridge_funcs {
 	 * called when &drm_bridge_funcs.atomic_check() is implemented, so only
 	 * one of them should be provided.
 	 *
+	 * If drivers need to tweak &drm_bridge_state.input_bus_cfg.flags or
+	 * &drm_bridge_state.output_bus_cfg.flags it should should happen in
+	 * this function. By default the &drm_bridge_state.output_bus_cfg.flags
+	 * field is set to the next bridge
+	 * &drm_bridge_state.input_bus_cfg.flags value or
+	 * &drm_connector.display_info.bus_flags if the bridge is the last
+	 * element in the chain.
+	 *
 	 * RETURNS:
 	 * zero if the check passed, a negative error code otherwise.
 	 */
@@ -578,6 +652,14 @@  void drm_atomic_bridge_chain_pre_enable(struct drm_bridge *bridge,
 void drm_atomic_bridge_chain_enable(struct drm_bridge *bridge,
 				    struct drm_atomic_state *state);
 
+u32 *
+drm_atomic_helper_bridge_propagate_bus_fmt(struct drm_bridge *bridge,
+					struct drm_bridge_state *bridge_state,
+					struct drm_crtc_state *crtc_state,
+					struct drm_connector_state *conn_state,
+					u32 output_fmt,
+					unsigned int *num_input_fmts);
+
 #ifdef CONFIG_DRM_PANEL_BRIDGE
 struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel);
 struct drm_bridge *drm_panel_bridge_add_typed(struct drm_panel *panel,