I want to split up a few more things and document some details better (like how exactly to subclass drm_atomic_state). And maybe also split up the helpers a bit per-topic, but this should be a ok-ish start for better atomic overview.
v2: Spelling and clarifications (Eric).
v3: Implement suggestion from Gabriel to fix the graph.
Cc: Gabriel Krisman Bertazi krisman@collabora.co.uk Acked-by: Eric Anholt eric@anholt.net Cc: Eric Anholt eric@anholt.net Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com Cc: Harry Wentland harry.wentland@amd.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com --- Documentation/gpu/drm-kms-helpers.rst | 2 + Documentation/gpu/drm-kms.rst | 84 ++++++++++++++++++++++++++++++++++- 2 files changed, 85 insertions(+), 1 deletion(-)
diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst index 050ebe81d256..ac53c0b893f6 100644 --- a/Documentation/gpu/drm-kms-helpers.rst +++ b/Documentation/gpu/drm-kms-helpers.rst @@ -42,6 +42,8 @@ Modeset Helper Reference for Common Vtables .. kernel-doc:: include/drm/drm_modeset_helper_vtables.h :internal:
+.. _drm_atomic_helper: + Atomic Modeset Helper Functions Reference =========================================
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index a504d9ee4d94..eb9d29865c41 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -189,8 +189,90 @@ multiple times to different objects using :c:func:`drm_object_attach_property() .. kernel-doc:: drivers/gpu/drm/drm_mode_object.c :export:
+Atomic Mode Setting +=================== + + +.. kernel-render:: DOT + :alt: Mode Objects and Properties + :caption: Mode Objects and Properties + + digraph { + node [shape=box] + + subgraph cluster_state { + style=dashed + label="Free-standing state" + + "drm_atomic_state" -> "duplicated drm_plane_state A" + "drm_atomic_state" -> "duplicated drm_plane_state B" + "drm_atomic_state" -> "duplicated drm_crtc_state" + "drm_atomic_state" -> "duplicated drm_connector_state" + "drm_atomic_state" -> "duplicated driver private state" + } + + subgraph cluster_current { + style=dashed + label="Current state" + + "drm_device" -> "drm_plane A" + "drm_device" -> "drm_plane B" + "drm_device" -> "drm_crtc" + "drm_device" -> "drm_connector" + "drm_device" -> "driver private object" + + "drm_plane A" -> "drm_plane_state A" + "drm_plane B" -> "drm_plane_state B" + "drm_crtc" -> "drm_crtc_state" + "drm_connector" -> "drm_connector_state" + "driver private object" -> "driver private state" + } + + "drm_atomic_state" -> "drm_device" [label="atomic_commit"] + "duplicated drm_plane_state A" -> "drm_device"[style=invis] + } + +Atomic provides transactional modeset (including planes) updates, but a +bit differently from the usual transactional approach of try-commit and +rollback: + +- Firstly, no hardware changes are allowed when the commit would fail. This + allows us to implement the DRM_MODE_ATOMIC_TEST_ONLY mode, which allows + userspace to explore whether certain configurations would work or not. + +- This would still allow setting and rollback of just the software state, + simplifying conversion of existing drivers. But auditing drivers for + correctness of the atomic_check code becomes really hard with that: Rolling + back changes in data structures all over the place is hard to get right. + +- Lastly, for backwards compatibility and to support all use-cases, atomic + updates need to be incremental and be able to execute in parallel. Hardware + doesn't always allow it, but where possible plane updates on different CRTCs + should not interfere, and not get stalled due to output routing changing on + different CRTCs. + +Taken all together there's two consequences for the atomic design: + +- The overall state is split up into per-object state structures: + :c:type:`struct drm_plane_state <drm_plane_state>` for planes, :c:type:`struct + drm_crtc_state <drm_crtc_state>` for CRTCs and :c:type:`struct + drm_connector_state <drm_connector_state` for connectors. These are the only + objects with userspace-visible and settable state. For internal state drivers + can subclass these structures through embeddeding, or add entirely new state + structures for their globally shared hardware functions. + +- An atomic update is assembled and validated as an enterily free-standing pile + of structures within the :c:type:`drm_atomic_state <drm_atomic_state>` + container. Again drivers can subclass that container for their own state + structure tracking needs. Only when a state is committed is it applied to the + driver and modeset objects. This way rolling back an update boils down to + releasing memory and unreferencing objects like framebuffers. + +Read on in this chapter, and also in :ref:`drm_atomic_helper` for more detailed +coverage of specific topics. + Atomic Mode Setting Function Reference -====================================== +--------------------------------------
.. kernel-doc:: include/drm/drm_atomic.h :internal: