[PATCH 4/4] drm/atomic-helper: Add select_output_bus_format callback

[Anatoliy Klymenko]

Add select_output_bus_format to CRTC atomic helpers callbacks. This
callback Will allow CRTC to participate in media bus format negotiation
over connected DRM bridge chain and impose CRTC-specific restrictions.
A good example is 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 FPGA are usually achieved by synthesizing IP with different
parameters.

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.

Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@xxxxxxx>
---
 drivers/gpu/drm/drm_bridge.c             | 19 +++++++++++++++++--
 include/drm/drm_modeset_helper_vtables.h | 31 +++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 521a71c61b16..453ae3d174b4 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -32,6 +32,7 @@
 #include <drm/drm_edid.h>
 #include <drm/drm_encoder.h>
 #include <drm/drm_file.h>
+#include <drm/drm_modeset_helper_vtables.h>
 #include <drm/drm_of.h>
 #include <drm/drm_print.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 +935,20 @@ 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 = in_bus_fmts[0];
+		if (crtc->helper_private &&
+		    crtc->helper_private->select_output_bus_format) {
+			in_fmt = crtc->helper_private->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/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 881b03e4dc28..7c21ae1fe3ad 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -489,6 +489,37 @@ 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 first connected DRM bridge to negotiate input media
+	 * bus format. CRTC is expected to pick preferable media formats from
+	 * the list supported by the DRM bridge chain.
+	 *
+	 * This callback is optional.
+	 *
+	 * Parameters:
+	 *
+	 * crtc:
+	 *     The CRTC.
+	 * crcs_state:
+	 *     New CRTC state.
+	 * supported_fmts:
+	 *     List of input bus formats supported by the bridge.
+	 * 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,
+					int num_supported_fmts);
 };
 
 /**

-- 
2.25.1