Clean up the drm_bridge overview documentation, and expand the
operations documentation to provide more details on API usage.
Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
---
Documentation/gpu/drm-kms-helpers.rst | 6 +--
drivers/gpu/drm/drm_bridge.c | 76 ++++++++++++++++++++-------
2 files changed, 60 insertions(+), 22 deletions(-)
diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
index 9668a7fe2408..fe155c6ae175 100644
--- a/Documentation/gpu/drm-kms-helpers.rst
+++ b/Documentation/gpu/drm-kms-helpers.rst
@@ -139,11 +139,11 @@ Overview
.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
:doc: overview
-Default bridge callback sequence
---------------------------------
+Bridge Operations
+-----------------
.. kernel-doc:: drivers/gpu/drm/drm_bridge.c
- :doc: bridge callbacks
+ :doc: bridge operations
Bridge Helper Reference
diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 68ab933ee430..5f55a9e17a7c 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -39,25 +39,36 @@
* encoder chain.
*
* A bridge is always attached to a single &drm_encoder at a time, but can be
- * either connected to it directly, or through an intermediate bridge::
+ * either connected to it directly, or through a chain of bridges::
*
- * encoder ---> bridge B ---> bridge A
+ * [ CRTC ---> ] Encoder ---> Bridge A ---> Bridge B
*
- * Here, the output of the encoder feeds to bridge B, and that furthers feeds to
- * bridge A.
+ * Here, the output of the encoder feeds to bridge A, and that furthers feeds to
+ * bridge B. Bridge chains can be arbitrarily long, and shall be fully linear:
+ * Chaining multiple bridges to the output of a bridge, or the same bridge to
+ * the output of different bridges, is not supported.
*
- * The driver using the bridge is responsible to make the associations between
- * the encoder and bridges. Once these links are made, the bridges will
- * participate along with encoder functions to perform mode_set/enable/disable
- * through the ops provided in &drm_bridge_funcs.
+ * Display drivers are responsible for linking encoders with the first bridge
+ * in the chains. This is done by acquiring the appropriate bridge with
+ * of_drm_find_bridge() or drm_of_find_panel_or_bridge(), or creating it for a
+ * panel with drm_panel_bridge_add_typed() (or the managed version
+ * devm_drm_panel_bridge_add_typed()). Once acquired, the bridge shall be
+ * attached to the encoder with a call to drm_bridge_attach().
*
- * drm_bridge, like drm_panel, aren't drm_mode_object entities like planes,
+ * Bridges are responsible for linking themselves with the next bridge in the
+ * chain, if any. This is done the same way as for encoders, with the call to
+ * drm_bridge_attach() occurring in the &drm_bridge_funcs.attach operation.
+ *
+ * Once these links are created, the bridges will automatically participate
+ * along with encoder functions to perform mode setting, enable and disable
+ * through the corresponding operations provided in &drm_bridge_funcs. This
+ * requires no intervention from display drivers.
+ *
+ * &drm_bridge, like &drm_panel, aren't &drm_mode_object entities like planes,
* CRTCs, encoders or connectors and hence are not visible to userspace. They
* just provide additional hooks to get the desired output at the end of the
* encoder chain.
*
- * Bridges can also be chained up using the &drm_bridge.chain_node field.
- *
* Both legacy CRTC helpers and the new atomic modeset helpers support bridges.
*/
@@ -212,14 +223,41 @@ void drm_bridge_detach(struct drm_bridge *bridge)
}
/**
- * DOC: bridge callbacks
- *
- * The &drm_bridge_funcs ops are populated by the bridge driver. The DRM
- * internals (atomic and CRTC helpers) use the helpers defined in drm_bridge.c
- * These helpers call a specific &drm_bridge_funcs op for all the bridges
- * during encoder configuration.
- *
- * For detailed specification of the bridge callbacks see &drm_bridge_funcs.
+ * DOC: bridge operations
+ *
+ * Bridge drivers expose operations through the &drm_bridge_funcs structure.
+ * The DRM internals (atomic and CRTC helpers) use the helpers defined in
+ * drm_bridge.c to call bridge operations. Those operations are divided in
+ * two big categories to support different parts of the bridge usage.
+ *
+ * - The encoder-related operations support control of the bridges in the
+ * chain, and are roughly counterparts to the &drm_encoder_helper_funcs
+ * operations. They are used by the legacy CRTC and the atomic modeset
+ * helpers to perform mode validation, fixup and setting, and enable and
+ * disable the bridge automatically.
+ *
+ * The enable and disable operations are split in
+ * &drm_bridge_funcs.pre_enable, &drm_bridge_funcs.enable,
+ * &drm_bridge_funcs.disable and &drm_bridge_funcs.post_disable to provide
+ * finer-grained control.
+ *
+ * Bridge drivers may implement the legacy version of those operations, or
+ * the atomic version (prefixed with atomic\_), in which case they shall also
+ * implement the atomic state bookkeeping operations
+ * (&drm_bridge_funcs.atomic_duplicate_state,
+ * &drm_bridge_funcs.atomic_destroy_state and &drm_bridge_funcs.reset).
+ * Mixing atomic and non-atomic versions of the operations is not supported.
+ *
+ * - The bus format negotiation operations
+ * &drm_bridge_funcs.atomic_get_output_bus_fmts and
+ * &drm_bridge_funcs.atomic_get_input_bus_fmts allow bridge drivers to
+ * negotiate the formats transmitted between bridges in the chain when
+ * multiple formats are supported. Negotiation for formats is performed
+ * transparently for display drivers by the atomic modeset helpers. Only
+ * atomic versions of those operations exist, bridge drivers that need to
+ * implement them shall thus also implement the atomic version of the
+ * encoder-related operations. This feature is not supported by the legacy
+ * CRTC helpers.
*/
/**
--
Regards,
Laurent Pinchart
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