[PATCH RFC 2/5] drm/bridge: add encoder support to specify bridge input format

[Neil Armstrong]

This patch adds a new format_set() callback to the bridge ops permitting
the encoder to specify the new input format and encoding.

This allows supporting the very specific HDMI2.0 YUV420 output mode
when the bridge cannot convert from RGB or YUV444 to YUV420.

In this case, the encode must downsample before the bridge and must
specify the bridge the new input bus format differs.

This will also help supporting the YUV420 mode where the bridge cannot
downsample, and also support 10bit, 12bit and 16bit output modes
when the bridge cannot convert between different bit depths.

Signed-off-by: Neil Armstrong <narmstrong at baylibre.com>
---
 drivers/gpu/drm/drm_bridge.c | 35 +++++++++++++++++++++++++++++++++++
 include/drm/drm_bridge.h     | 19 +++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 138b2711d389..b2ce2d3d070e 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -307,6 +307,41 @@ void drm_bridge_mode_set(struct drm_bridge *bridge,
 }
 EXPORT_SYMBOL(drm_bridge_mode_set);
 
+/**
+ * drm_bridge_format_set - setup with proposed input format and encoding for
+ *			   all bridges in the encoder chain
+ * @bridge: bridge control structure
+ * @input_bus_format: proposed input bus format for the bridge
+ * @input_encoding: proposed input encoding for this bridge
+ *
+ * Calls &drm_bridge_funcs.format_set op for all the bridges in the
+ * encoder chain, starting from the first bridge to the last.
+ *
+ * Note: the bridge passed should be the one closest to the encoder
+ *
+ * RETURNS:
+ * true on success, false if one of the bridge cannot handle the format
+ */
+bool drm_bridge_format_set(struct drm_bridge *bridge,
+			   const u32 input_bus_format,
+			   const u32 input_encoding)
+{
+	bool ret = true;
+
+	if (!bridge)
+		return true;
+
+	if (bridge->funcs->format_set)
+		ret = bridge->funcs->format_set(bridge, input_bus_format,
+						input_encoding);
+	if (ret)
+		return ret;
+
+	return drm_bridge_format_set(bridge->next, input_bus_format,
+				     input_encoding);
+}
+EXPORT_SYMBOL(drm_bridge_format_set);
+
 /**
  * drm_bridge_pre_enable - prepares for enabling all
  *			   bridges in the encoder chain
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 9da8c93f7976..223253b15763 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -198,6 +198,22 @@ struct drm_bridge_funcs {
 	void (*mode_set)(struct drm_bridge *bridge,
 			 const struct drm_display_mode *mode,
 			 const struct drm_display_mode *adjusted_mode);
+
+	/**
+	 * @format_set:
+	 *
+	 * This callback should configure the bridge for the given input bus
+	 * format and encoding. It is called after the @format_set callback
+	 * for the preceding element in the display pipeline has been called
+	 * already. If the bridge is the first element then this would be
+	 * &drm_encoder_helper_funcs.format_set. The display pipe (i.e.
+	 * clocks and timing signals) is off when this function is called.
+	 *
+	 * @returns: true in success, false is a bridge refuses the format
+	 */
+	bool (*format_set)(struct drm_bridge *bridge,
+			   const u32 input_bus_format,
+			   const u32 input_encoding);
 	/**
 	 * @pre_enable:
 	 *
@@ -312,6 +328,9 @@ void drm_bridge_post_disable(struct drm_bridge *bridge);
 void drm_bridge_mode_set(struct drm_bridge *bridge,
 			 const struct drm_display_mode *mode,
 			 const struct drm_display_mode *adjusted_mode);
+bool drm_bridge_format_set(struct drm_bridge *bridge,
+			   const u32 input_bus_format,
+			   const u32 input_encoding);
 void drm_bridge_pre_enable(struct drm_bridge *bridge);
 void drm_bridge_enable(struct drm_bridge *bridge);
 
-- 
2.21.0