Daniel Vetter daniel.vetter@ffwll.ch writes:

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.

One thing I failed at is getting DOT to layout the overview graph how I want it. The highlevel structure I want is:

Free-standing State

Current State

i.e. one over the other. Currently it lays it out side-by-side, but not even that really - "Current State" is somewhat offset below. Makes the graph look like garbage, and also way too wide for proper rendering. Ideas appreciated.

Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com Cc: Harry Wentland harry.wentland@amd.com Signed-off-by: Daniel Vetter daniel.vetter@intel.com

Thanks for writing these docs. I wish I had them back when I was starting vc4's atomic code! With the two little spelling nits fixed, 3-5 are:

Acked-by: Eric Anholt eric@anholt.net

A few copyedits on this one below, but it sounds like you don't want to push quite yet while you sort out the rendering.

---

Documentation/gpu/drm-kms-helpers.rst | 2 + Documentation/gpu/drm-kms.rst | 85 ++++++++++++++++++++++++++++++++++- 2 files changed, 86 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 20378881445f..979cee853bb1 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -189,8 +189,91 @@ 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 +===================

+.. FIXME: The I want the below graph to be laid out so that the 2 subgraph

• clusters are below each another. But I failed.

+.. 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"]
  

• }

+Essentially atomic is transactional modeset (including planes) updates, but +compared to the usual transactional approach of try-commit and rollback on +failure atomic modesetting is a bit different:

Maybe reword:

"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 allows setting and rollback of just the software state,

"allow"

• simplifying conversion of existing drivers. But auditing drivers for
• correctness of the atomic_check code because really hard with that.

s/because/becomes/?

+Taken all together there's two consequence for the atomic design:

"consequences"

+- 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 commit is it applied to the

"is committed"

• driver and modeset objects. This way rolling back an update boils down to
• releasing memory and unreference objects like framebuffers.

"unreferencing"