Commit 97ecfff4 authored by Simon Ser's avatar Simon Ser
Browse files

drm/doc: document the type plane property 



Add a new entry for "type" in the section for standard plane properties.

v3: improve paragraph about mixing legacy IOCTLs with explicit usage,
note that a driver may support cursors without cursor planes (Daniel)

v4: fixing rebase gone wrong

v5:
- Fix typo (Daniel)
- Mention CAP_ATOMIC instead of CAP_UNIVERSAL_PLANES when referring to
  atomic test-only commits (Daniel)
- Add newlines at end of sections (Daniel)

Signed-off-by: default avatarSimon Ser <contact@emersion.fr>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: default avatarPekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210115110626.12233-2-contact@emersion.fr
parent 7e5d1e12

drivers/gpu/drm/drm_plane.c

+54 −4
Original line number Diff line number Diff line
@@ -50,10 +50,8 @@ 
 * &struct drm_plane (possibly as part of a larger structure) and registers it

 * with a call to drm_universal_plane_init().

 *

 * The type of a plane is exposed in the immutable "type" enumeration property,

 * which has one of the following values: "Overlay", "Primary", "Cursor" (see

 * enum drm_plane_type). A plane can be compatible with multiple CRTCs, see

 * &drm_plane.possible_crtcs.

 * Each plane has a type, see enum drm_plane_type. A plane can be compatible

 * with multiple CRTCs, see &drm_plane.possible_crtcs.

 *

 * Each CRTC must have a unique primary plane userspace can attach to enable

 * the CRTC. In other words, userspace must be able to attach a different
@@ -73,6 +71,58 @@ 
 *

 * DRM planes have a few standardized properties:

 *

 * type:

 *     Immutable property describing the type of the plane.

 *

 *     For user-space which has enabled the &DRM_CLIENT_CAP_ATOMIC capability,

 *     the plane type is just a hint and is mostly superseded by atomic

 *     test-only commits. The type hint can still be used to come up more

 *     easily with a plane configuration accepted by the driver.

 *

 *     The value of this property can be one of the following:

 *

 *     "Primary":

 *         To light up a CRTC, attaching a primary plane is the most likely to

 *         work if it covers the whole CRTC and doesn't have scaling or

 *         cropping set up.

 *

 *         Drivers may support more features for the primary plane, user-space

 *         can find out with test-only atomic commits.

 *

 *         Some primary planes are implicitly used by the kernel in the legacy

 *         IOCTLs &DRM_IOCTL_MODE_SETCRTC and &DRM_IOCTL_MODE_PAGE_FLIP.

 *         Therefore user-space must not mix explicit usage of any primary

 *         plane (e.g. through an atomic commit) with these legacy IOCTLs.

 *

 *     "Cursor":

 *         To enable this plane, using a framebuffer configured without scaling

 *         or cropping and with the following properties is the most likely to

 *         work:

 *

 *         - If the driver provides the capabilities &DRM_CAP_CURSOR_WIDTH and

 *           &DRM_CAP_CURSOR_HEIGHT, create the framebuffer with this size.

 *           Otherwise, create a framebuffer with the size 64x64.

 *         - If the driver doesn't support modifiers, create a framebuffer with

 *           a linear layout. Otherwise, use the IN_FORMATS plane property.

 *

 *         Drivers may support more features for the cursor plane, user-space

 *         can find out with test-only atomic commits.

 *

 *         Some cursor planes are implicitly used by the kernel in the legacy

 *         IOCTLs &DRM_IOCTL_MODE_CURSOR and &DRM_IOCTL_MODE_CURSOR2.

 *         Therefore user-space must not mix explicit usage of any cursor

 *         plane (e.g. through an atomic commit) with these legacy IOCTLs.

 *

 *         Some drivers may support cursors even if no cursor plane is exposed.

 *         In this case, the legacy cursor IOCTLs can be used to configure the

 *         cursor.

 *

 *     "Overlay":

 *         Neither primary nor cursor.

 *

 *         Overlay planes are the only planes exposed when the

 *         &DRM_CLIENT_CAP_UNIVERSAL_PLANES capability is disabled.

 *

 * IN_FORMATS:

 *     Blob property which contains the set of buffer format and modifier

 *     pairs supported by this plane. The blob is a struct