8f6ea27b2f
Currently the property docs don't specify whether it's okay for two planes to have the same zpos value and what user-space should expect in this case. The unspoken, legacy rule used in the past was to make user-space figure out the zpos from object IDs. However some drivers break this rule, that's why the ordering is documented as unspecified in case the zpos property is missing. User-space should rely on the zpos property only. There are some cases in which user-space might read identical zpos values for different planes. For instance, in case the property is mutable, user-space might set two planes' zpos to the same value. This is necessary to support user-space using the legacy DRM API where atomic commits are not possible: user-space needs to update the planes' zpos one by one. Because of this, user-space should handle multiple planes with the same zpos. While at it, remove the assumption that zpos is only for overlay planes. Additionally, update the drm_plane_state.zpos docs to clarify that zpos disambiguation via plane object IDs is a recommendation for drivers, not something user-space can rely on. In other words, when user-space sets the same zpos on two planes, drivers should rely on the plane object ID. v2: clarify drm_plane_state.zpos docs (Daniel) v3: zpos is for all planes (Marius, Daniel) v4: completely reword the drm_plane_state.zpos docs to make it clear the recommendation to use plane IDs is for drivers in case user-space uses duplicate zpos values (Pekka) v5: reword commit message (Pekka, James) v6: remove mention of Arm GPUs having planes which can't overlap, because this isn't uAPI yet (Daniel) Signed-off-by: Simon Ser <contact@emersion.fr> Reviewed-by: Pekka Paalanen <ppaalanen@gmail.com> Cc: Marius Vlad <marius.vlad@collabora.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: James Qian Wang <james.qian.wang@arm.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/T5nHrvXH0GKOp6ONaFHk-j2cwEb4_4C_sBz9rNw8mmPACuut-DQqC74HMAFKZH3_Q15E8a3YnmKCxap-djKA71VVZv_T-tFxaB0he13O7yA=@emersion.fr
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.