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

Anatoliy Klymenko
2024-02-27T04:45:21Z

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@amd.com>
---
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