Hi Daniel, On Sat, Feb 22, 2020 at 04:32:58PM +0100, Daniel Vetter wrote: > On Sat, Feb 22, 2020 at 4:01 PM Laurent Pinchart 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. Very good point, I'll fix this in v7.1. > > + * &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! My (sometimes slightly masochistic) pleasure :-) -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
