[PATCH v4 7/7] drm/atomic-helper: Add select_output_bus_format callback

[Anatoliy Klymenko]

Add optional drm_crtc_helper_funcs.select_output_bus_format callback. This
callback allows to negotiate compatible media bus format on the link
between CRTC and connected DRM encoder or DRM bridge chain. A good usage
example is the CRTC implemented as FPGA soft IP. This kind of CRTC will
most certainly support a single output media bus format, as supporting
multiple runtime options consumes extra FPGA resources. A variety of
options for the FPGA designs are usually achieved by synthesizing IP with
different parameters.

Add drm_helper_crtc_select_output_bus_format that wraps
drm_crtc_helper_funcs.select_output_bus_format.

Incorporate select_output_bus_format callback into the format negotiation
stage to fix the input bus format of the first DRM bridge in the chain.

Save negotiated output media bus format in drm_crtc_state.

Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@xxxxxxx>
---
 drivers/gpu/drm/drm_bridge.c             | 14 ++++++++++--
 drivers/gpu/drm/drm_crtc_helper.c        | 38 ++++++++++++++++++++++++++++++++
 include/drm/drm_crtc.h                   | 11 +++++++++
 include/drm/drm_crtc_helper.h            |  5 +++++
 include/drm/drm_modeset_helper_vtables.h | 30 +++++++++++++++++++++++++
 5 files changed, 96 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 521a71c61b16..955ca108cd4b 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -28,6 +28,7 @@
 
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_bridge.h>
+#include <drm/drm_crtc_helper.h>
 #include <drm/drm_debugfs.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_encoder.h>
@@ -879,7 +880,8 @@ static int select_bus_fmt_recursive(struct drm_bridge *first_bridge,
 	unsigned int i, num_in_bus_fmts = 0;
 	struct drm_bridge_state *cur_state;
 	struct drm_bridge *prev_bridge;
-	u32 *in_bus_fmts;
+	struct drm_crtc *crtc = crtc_state->crtc;
+	u32 *in_bus_fmts, in_fmt;
 	int ret;
 
 	prev_bridge = drm_bridge_get_prev_bridge(cur_bridge);
@@ -933,7 +935,15 @@ static int select_bus_fmt_recursive(struct drm_bridge *first_bridge,
 		return -ENOMEM;
 
 	if (first_bridge == cur_bridge) {
-		cur_state->input_bus_cfg.format = in_bus_fmts[0];
+		in_fmt = drm_helper_crtc_select_output_bus_format(crtc,
+							crtc_state,
+							in_bus_fmts,
+							num_in_bus_fmts);
+		if (!in_fmt) {
+			kfree(in_bus_fmts);
+			return -ENOTSUPP;
+		}
+		cur_state->input_bus_cfg.format = in_fmt;
 		cur_state->output_bus_cfg.format = out_bus_fmt;
 		kfree(in_bus_fmts);
 		return 0;
diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 2dafc39a27cb..4d3aa39c8a82 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -1055,3 +1055,41 @@ int drm_helper_force_disable_all(struct drm_device *dev)
 	return ret;
 }
 EXPORT_SYMBOL(drm_helper_force_disable_all);
+
+/**
+ * drm_helper_crtc_select_output_bus_format - Select output media bus format
+ * @crtc: The CRTC to query
+ * @crtc_state: The new CRTC state
+ * @supported_fmts: List of media bus format options to pick from
+ * @num_supported_fmts: Number of media bus formats in @supported_fmts list
+ *
+ * Encoder drivers may call this helper to give the connected CRTC a chance to
+ * select compatible or preffered media bus format to use over the CRTC encoder
+ * link. Encoders should provide list of supported input MEDIA_BUS_FMT_* for
+ * CRTC to pick from. CRTC driver is expected to select preferred media bus
+ * format from the list and, once enabled, generate the signal accordingly.
+ *
+ * Returns:
+ * Selected preferred media bus format or 0 if CRTC does not support any from
+ * @supported_fmts list.
+ */
+u32 drm_helper_crtc_select_output_bus_format(struct drm_crtc *crtc,
+					     struct drm_crtc_state *crtc_state,
+					     const u32 *supported_fmts,
+					     unsigned int num_supported_fmts)
+{
+	if (!crtc || !crtc_state || !supported_fmts || !num_supported_fmts)
+		return 0;
+
+	if (!crtc->helper_private ||
+	    !crtc->helper_private->select_output_bus_format)
+		crtc_state->output_bus_format = supported_fmts[0];
+	else
+		crtc_state->output_bus_format =
+			crtc->helper_private->select_output_bus_format(crtc,
+							crtc_state,
+							supported_fmts,
+							num_supported_fmts);
+	return crtc_state->output_bus_format;
+}
+EXPORT_SYMBOL(drm_helper_crtc_select_output_bus_format);
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 8b48a1974da3..cdaa27f50af7 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -317,6 +317,17 @@ struct drm_crtc_state {
 	 */
 	enum drm_scaling_filter scaling_filter;
 
+	/**
+	 * @output_bus_format:
+	 *
+	 * CRTC output media bus format of the video signal negotiated between
+	 * CRTC and encoder. This value should be one of MEDIA_BUS_FMT*
+	 * from uapi/linux/media-bus-format.h. It is safe to ignore
+	 * @output_bus_format if CRTC doesn't support multiple output bus format
+	 * options.
+	 */
+	u32 output_bus_format;
+
 	/**
 	 * @event:
 	 *
diff --git a/include/drm/drm_crtc_helper.h b/include/drm/drm_crtc_helper.h
index 8c886fc46ef2..b7eb52f3ce41 100644
--- a/include/drm/drm_crtc_helper.h
+++ b/include/drm/drm_crtc_helper.h
@@ -38,6 +38,7 @@
 struct drm_atomic_state;
 struct drm_connector;
 struct drm_crtc;
+struct drm_crtc_state;
 struct drm_device;
 struct drm_display_mode;
 struct drm_encoder;
@@ -61,5 +62,9 @@ int drm_helper_connector_dpms(struct drm_connector *connector, int mode);
 
 void drm_helper_resume_force_mode(struct drm_device *dev);
 int drm_helper_force_disable_all(struct drm_device *dev);
+u32 drm_helper_crtc_select_output_bus_format(struct drm_crtc *crtc,
+					     struct drm_crtc_state *crtc_state,
+					     const u32 *supported_fmts,
+					     unsigned int num_supported_fmts);
 
 #endif
diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 881b03e4dc28..6d5a081e21a4 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -489,6 +489,36 @@ struct drm_crtc_helper_funcs {
 				     bool in_vblank_irq, int *vpos, int *hpos,
 				     ktime_t *stime, ktime_t *etime,
 				     const struct drm_display_mode *mode);
+
+	/**
+	 * @select_output_bus_format
+	 *
+	 * Called by the connected DRM encoder to negotiate input media bus
+	 * format. CRTC is expected to pick preferable media formats from the
+	 * list provided by the DRM encoder.
+	 *
+	 * This callback is optional.
+	 *
+	 * Parameters:
+	 *
+	 * crtc:
+	 *     The CRTC.
+	 * crcs_state:
+	 *     New CRTC state.
+	 * supported_fmts:
+	 *     List of input bus formats supported by the encoder.
+	 * num_supported_fmts:
+	 *     Number of formats in the list.
+	 *
+	 * Returns:
+	 *
+	 * Preferred bus format from the list or 0 if CRTC doesn't support any
+	 * from the provided list.
+	 */
+	u32 (*select_output_bus_format)(struct drm_crtc *crtc,
+					struct drm_crtc_state *crtc_state,
+					const u32 *supported_fmts,
+					unsigned int num_supported_fmts);
 };
 
 /**

-- 
2.25.1