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@ideasonboard.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch --- Change since v7:
- Detail how bridge operations are used by atomic helpers --- Documentation/gpu/drm-kms-helpers.rst | 6 +- drivers/gpu/drm/drm_bridge.c | 101 +++++++++++++++++++------- 2 files changed, 79 insertions(+), 28 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..52dfc67a6cf8 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -39,26 +39,50 @@ * 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:: - * - * encoder ---> bridge B ---> bridge A - * - * Here, the output of the encoder feeds to bridge B, and that furthers feeds to - * bridge A. - * - * 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. - * - * drm_bridge, like drm_panel, aren't drm_mode_object entities like planes, + * either connected to it directly, or through a chain of bridges:: + * + * [ CRTC ---> ] Encoder ---> Bridge A ---> Bridge B + * + * 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. + * + * 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(). + * + * 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 can participate along with encoder + * functions to perform mode validation and fixup (through + * drm_bridge_chain_mode_valid() and drm_atomic_bridge_chain_check()), mode + * setting (through drm_bridge_chain_mode_set()), enable (through + * drm_atomic_bridge_chain_pre_enable() and drm_atomic_bridge_chain_enable()) + * and disable (through drm_atomic_bridge_chain_disable() and + * drm_atomic_bridge_chain_post_disable()). Those functions call the + * corresponding operations provided in &drm_bridge_funcs in sequence for all + * bridges in the chain. + * + * For display drivers that use the atomic helpers + * drm_atomic_helper_check_modeset(), + * drm_atomic_helper_commit_modeset_enables() and + * drm_atomic_helper_commit_modeset_disables() (either directly in hand-rolled + * commit check and commit tail handlers, or through the higher-level + * drm_atomic_helper_check() and drm_atomic_helper_commit_tail() or + * drm_atomic_helper_commit_tail_rpm() helpers), this is done transparently and + * requires no intervention from the driver. For other drivers, the relevant + * DRM bridge chain functions shall be called manually. + * + * &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. */
static DEFINE_MUTEX(bridge_lock); @@ -212,14 +236,41 @@ 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. */
/**