drm/bridge: display-connector: implement bus fmts callbacks

Since this bridge is tied to the connector, it acts like a passthrough,
so concerning the output & input bus formats, either pass the bus formats from the
previous bridge or return fallback data like done in the bridge function:
drm_atomic_bridge_chain_select_bus_fmts() & select_bus_fmt_recursive.

This permits avoiding skipping the negociation if the remaining bridge chain has
all the bits in place.

Without this bus fmt negociation breaks on drm/meson HDMI pipeline when attaching
dw-hdmi with DRM_BRIDGE_ATTACH_NO_CONNECTOR, because the last bridge of the
display-connector doesn't implement buf fmt callbacks and MEDIA_BUS_FMT_FIXED
is used leading to select an unsupported default bus format from dw-hdmi.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211020123947.2585572-2-narmstrong@baylibre.com

drivers/gpu/drm/bridge/display-connector.c

@@ -13,6 +13,7 @@
 #include <linux/platform_device.h>
 #include <linux/regulator/consumer.h>
 
+#include <drm/drm_atomic_helper.h>
 #include <drm/drm_bridge.h>
 #include <drm/drm_edid.h>
 
@@ -87,10 +88,95 @@ static struct edid *display_connector_get_edid(struct drm_bridge *bridge,
 	return drm_get_edid(connector, conn->bridge.ddc);
 }
 
+/*
+ * Since this bridge is tied to the connector, it acts like a passthrough,
+ * so concerning the output bus formats, either pass the bus formats from the
+ * previous bridge or return fallback data like done in the bridge function:
+ * drm_atomic_bridge_chain_select_bus_fmts().
+ * This supports negotiation if the bridge chain has all bits in place.
+ */
+static u32 *display_connector_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)
+{
+	struct drm_bridge *prev_bridge = drm_bridge_get_prev_bridge(bridge);
+	struct drm_bridge_state *prev_bridge_state;
+
+	if (!prev_bridge || !prev_bridge->funcs->atomic_get_output_bus_fmts) {
+		struct drm_connector *conn = conn_state->connector;
+		u32 *out_bus_fmts;
+
+		*num_output_fmts = 1;
+		out_bus_fmts = kmalloc(sizeof(*out_bus_fmts), GFP_KERNEL);
+		if (!out_bus_fmts)
+			return NULL;
+
+		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;
+
+		return out_bus_fmts;
+	}
+
+	prev_bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
+							    prev_bridge);
+
+	return prev_bridge->funcs->atomic_get_output_bus_fmts(prev_bridge, prev_bridge_state,
+							      crtc_state, conn_state,
+							      num_output_fmts);
+}
+
+/*
+ * Since this bridge is tied to the connector, it acts like a passthrough,
+ * so concerning the input bus formats, either pass the bus formats from the
+ * previous bridge or MEDIA_BUS_FMT_FIXED (like select_bus_fmt_recursive())
+ * when atomic_get_input_bus_fmts is not supported.
+ * This supports negotiation if the bridge chain has all bits in place.
+ */
+static u32 *display_connector_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)
+{
+	struct drm_bridge *prev_bridge = drm_bridge_get_prev_bridge(bridge);
+	struct drm_bridge_state *prev_bridge_state;
+
+	if (!prev_bridge || !prev_bridge->funcs->atomic_get_input_bus_fmts) {
+		u32 *in_bus_fmts;
+
+		*num_input_fmts = 1;
+		in_bus_fmts = kmalloc(sizeof(*in_bus_fmts), GFP_KERNEL);
+		if (!in_bus_fmts)
+			return NULL;
+
+		in_bus_fmts[0] = MEDIA_BUS_FMT_FIXED;
+
+		return in_bus_fmts;
+	}
+
+	prev_bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
+							    prev_bridge);
+
+	return prev_bridge->funcs->atomic_get_input_bus_fmts(prev_bridge, prev_bridge_state,
+							     crtc_state, conn_state, output_fmt,
+							     num_input_fmts);
+}
+
 static const struct drm_bridge_funcs display_connector_bridge_funcs = {
 	.attach = display_connector_attach,
 	.detect = display_connector_detect,
 	.get_edid = display_connector_get_edid,
+	.atomic_get_output_bus_fmts = display_connector_get_output_bus_fmts,
+	.atomic_get_input_bus_fmts = display_connector_get_input_bus_fmts,
+	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
+	.atomic_reset = drm_atomic_helper_bridge_reset,
 };
 
 static irqreturn_t display_connector_hpd_irq(int irq, void *arg)