[PATCH v2 6/8] drm/atomic-helper: Add select_output_bus_format callback

Anatoliy Klymenko
2024-03-13T00:55:15Z

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.

Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@amd.com>
---
drivers/gpu/drm/drm_bridge.c | 14 +++++++++++--
drivers/gpu/drm/drm_crtc_helper.c | 36 ++++++++++++++++++++++++++++++++
include/drm/drm_crtc_helper.h | 5 +++++
include/drm/drm_modeset_helper_vtables.h | 30 ++++++++++++++++++++++++++
4 files changed, 83 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..f2e12a3c4e5f 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -1055,3 +1055,39 @@ 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 || !supported_fmts || !num_supported_fmts)
+ return 0;
+
+ if (!crtc->helper_private ||
+ !crtc->helper_private->select_output_bus_format)
+ return supported_fmts[0];
+
+ return crtc->helper_private->select_output_bus_format(crtc,
+ crtc_state,
+ supported_fmts,
+ num_supported_fmts);
+}
+EXPORT_SYMBOL(drm_helper_crtc_select_output_bus_format);
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