On Sat, Feb 22, 2020 at 4:01 PM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > 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. This is not quite correct, since this fully automatic behaviour only happens if you're using the drm_atomic_helper_modeset_disables and drm_atomic_helper_modeset_enables functions. If you roll your own (which is totally fine, that's why atomic helpers are modular), you need to call the relevant bridge functions yourself. I think would be good to clarify that and add links to the relevant bridge functions in a sentence here too. At least the bridge chain functions involved in this modeset stuff. Also, probe side only happens if you use drm_atomic_helper_check_modeset(), good to mention that too and the set of relevant bridge chain helpers for ti. > + * &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. > */ With the one gap/slight incorrectness addressed: Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> Thanks a lot for keeping our docs relevant! Cheers, Daniel > > /** > -- > Regards, > > Laurent Pinchart > -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
