mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-23 09:19:51 +00:00
![Brian Starkey](/assets/img/avatar_default.png)
AFBC is a flexible, proprietary, lossless compression protocol and format, with a number of defined DRM format modifiers. To facilitate consistency and compatibility between different AFBC producers and consumers, document the expectations for usage of the AFBC DRM format modifiers in a new .rst chapter. Signed-off-by: Brian Starkey <brian.starkey@arm.com> Reviewed-by: Liviu Dudau <liviu.dudau@arm.com> [Updated MAINTAINERS entry to show that "Mali DP Maintainers" is actually a mailing list and added an SPDX-License-Identifier to the documentation] Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
235 lines
7.3 KiB
ReStructuredText
235 lines
7.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
|
|
|
|
===================================
|
|
Arm Framebuffer Compression (AFBC)
|
|
===================================
|
|
|
|
AFBC is a proprietary lossless image compression protocol and format.
|
|
It provides fine-grained random access and minimizes the amount of
|
|
data transferred between IP blocks.
|
|
|
|
AFBC can be enabled on drivers which support it via use of the AFBC
|
|
format modifiers defined in drm_fourcc.h. See DRM_FORMAT_MOD_ARM_AFBC(*).
|
|
|
|
All users of the AFBC modifiers must follow the usage guidelines laid
|
|
out in this document, to ensure compatibility across different AFBC
|
|
producers and consumers.
|
|
|
|
Components and Ordering
|
|
=======================
|
|
|
|
AFBC streams can contain several components - where a component
|
|
corresponds to a color channel (i.e. R, G, B, X, A, Y, Cb, Cr).
|
|
The assignment of input/output color channels must be consistent
|
|
between the encoder and the decoder for correct operation, otherwise
|
|
the consumer will interpret the decoded data incorrectly.
|
|
|
|
Furthermore, when the lossless colorspace transform is used
|
|
(AFBC_FORMAT_MOD_YTR, which should be enabled for RGB buffers for
|
|
maximum compression efficiency), the component order must be:
|
|
|
|
* Component 0: R
|
|
* Component 1: G
|
|
* Component 2: B
|
|
|
|
The component ordering is communicated via the fourcc code in the
|
|
fourcc:modifier pair. In general, component '0' is considered to
|
|
reside in the least-significant bits of the corresponding linear
|
|
format. For example, COMP(bits):
|
|
|
|
* DRM_FORMAT_ABGR8888
|
|
|
|
* Component 0: R(8)
|
|
* Component 1: G(8)
|
|
* Component 2: B(8)
|
|
* Component 3: A(8)
|
|
|
|
* DRM_FORMAT_BGR888
|
|
|
|
* Component 0: R(8)
|
|
* Component 1: G(8)
|
|
* Component 2: B(8)
|
|
|
|
* DRM_FORMAT_YUYV
|
|
|
|
* Component 0: Y(8)
|
|
* Component 1: Cb(8, 2x1 subsampled)
|
|
* Component 2: Cr(8, 2x1 subsampled)
|
|
|
|
In AFBC, 'X' components are not treated any differently from any other
|
|
component. Therefore, an AFBC buffer with fourcc DRM_FORMAT_XBGR8888
|
|
encodes with 4 components, like so:
|
|
|
|
* DRM_FORMAT_XBGR8888
|
|
|
|
* Component 0: R(8)
|
|
* Component 1: G(8)
|
|
* Component 2: B(8)
|
|
* Component 3: X(8)
|
|
|
|
Please note, however, that the inclusion of a "wasted" 'X' channel is
|
|
bad for compression efficiency, and so it's recommended to avoid
|
|
formats containing 'X' bits. If a fourth component is
|
|
required/expected by the encoder/decoder, then it is recommended to
|
|
instead use an equivalent format with alpha, setting all alpha bits to
|
|
'1'. If there is no requirement for a fourth component, then a format
|
|
which doesn't include alpha can be used, e.g. DRM_FORMAT_BGR888.
|
|
|
|
Number of Planes
|
|
================
|
|
|
|
Formats which are typically multi-planar in linear layouts (e.g. YUV
|
|
420), can be encoded into one, or multiple, AFBC planes. As with
|
|
component order, the encoder and decoder must agree about the number
|
|
of planes in order to correctly decode the buffer. The fourcc code is
|
|
used to determine the number of encoded planes in an AFBC buffer,
|
|
matching the number of planes for the linear (unmodified) format.
|
|
Within each plane, the component ordering also follows the fourcc
|
|
code:
|
|
|
|
For example:
|
|
|
|
* DRM_FORMAT_YUYV: nplanes = 1
|
|
|
|
* Plane 0:
|
|
|
|
* Component 0: Y(8)
|
|
* Component 1: Cb(8, 2x1 subsampled)
|
|
* Component 2: Cr(8, 2x1 subsampled)
|
|
|
|
* DRM_FORMAT_NV12: nplanes = 2
|
|
|
|
* Plane 0:
|
|
|
|
* Component 0: Y(8)
|
|
|
|
* Plane 1:
|
|
|
|
* Component 0: Cb(8, 2x1 subsampled)
|
|
* Component 1: Cr(8, 2x1 subsampled)
|
|
|
|
Cross-device interoperability
|
|
=============================
|
|
|
|
For maximum compatibility across devices, the table below defines
|
|
canonical formats for use between AFBC-enabled devices. Formats which
|
|
are listed here must be used exactly as specified when using the AFBC
|
|
modifiers. Formats which are not listed should be avoided.
|
|
|
|
.. flat-table:: AFBC formats
|
|
|
|
* - Fourcc code
|
|
- Description
|
|
- Planes/Components
|
|
|
|
* - DRM_FORMAT_ABGR2101010
|
|
- 10-bit per component RGB, with 2-bit alpha
|
|
- Plane 0: 4 components
|
|
* Component 0: R(10)
|
|
* Component 1: G(10)
|
|
* Component 2: B(10)
|
|
* Component 3: A(2)
|
|
|
|
* - DRM_FORMAT_ABGR8888
|
|
- 8-bit per component RGB, with 8-bit alpha
|
|
- Plane 0: 4 components
|
|
* Component 0: R(8)
|
|
* Component 1: G(8)
|
|
* Component 2: B(8)
|
|
* Component 3: A(8)
|
|
|
|
* - DRM_FORMAT_BGR888
|
|
- 8-bit per component RGB
|
|
- Plane 0: 3 components
|
|
* Component 0: R(8)
|
|
* Component 1: G(8)
|
|
* Component 2: B(8)
|
|
|
|
* - DRM_FORMAT_BGR565
|
|
- 5/6-bit per component RGB
|
|
- Plane 0: 3 components
|
|
* Component 0: R(5)
|
|
* Component 1: G(6)
|
|
* Component 2: B(5)
|
|
|
|
* - DRM_FORMAT_ABGR1555
|
|
- 5-bit per component RGB, with 1-bit alpha
|
|
- Plane 0: 4 components
|
|
* Component 0: R(5)
|
|
* Component 1: G(5)
|
|
* Component 2: B(5)
|
|
* Component 3: A(1)
|
|
|
|
* - DRM_FORMAT_VUY888
|
|
- 8-bit per component YCbCr 444, single plane
|
|
- Plane 0: 3 components
|
|
* Component 0: Y(8)
|
|
* Component 1: Cb(8)
|
|
* Component 2: Cr(8)
|
|
|
|
* - DRM_FORMAT_VUY101010
|
|
- 10-bit per component YCbCr 444, single plane
|
|
- Plane 0: 3 components
|
|
* Component 0: Y(10)
|
|
* Component 1: Cb(10)
|
|
* Component 2: Cr(10)
|
|
|
|
* - DRM_FORMAT_YUYV
|
|
- 8-bit per component YCbCr 422, single plane
|
|
- Plane 0: 3 components
|
|
* Component 0: Y(8)
|
|
* Component 1: Cb(8, 2x1 subsampled)
|
|
* Component 2: Cr(8, 2x1 subsampled)
|
|
|
|
* - DRM_FORMAT_NV16
|
|
- 8-bit per component YCbCr 422, two plane
|
|
- Plane 0: 1 component
|
|
* Component 0: Y(8)
|
|
Plane 1: 2 components
|
|
* Component 0: Cb(8, 2x1 subsampled)
|
|
* Component 1: Cr(8, 2x1 subsampled)
|
|
|
|
* - DRM_FORMAT_Y210
|
|
- 10-bit per component YCbCr 422, single plane
|
|
- Plane 0: 3 components
|
|
* Component 0: Y(10)
|
|
* Component 1: Cb(10, 2x1 subsampled)
|
|
* Component 2: Cr(10, 2x1 subsampled)
|
|
|
|
* - DRM_FORMAT_P210
|
|
- 10-bit per component YCbCr 422, two plane
|
|
- Plane 0: 1 component
|
|
* Component 0: Y(10)
|
|
Plane 1: 2 components
|
|
* Component 0: Cb(10, 2x1 subsampled)
|
|
* Component 1: Cr(10, 2x1 subsampled)
|
|
|
|
* - DRM_FORMAT_YUV420_8BIT
|
|
- 8-bit per component YCbCr 420, single plane
|
|
- Plane 0: 3 components
|
|
* Component 0: Y(8)
|
|
* Component 1: Cb(8, 2x2 subsampled)
|
|
* Component 2: Cr(8, 2x2 subsampled)
|
|
|
|
* - DRM_FORMAT_YUV420_10BIT
|
|
- 10-bit per component YCbCr 420, single plane
|
|
- Plane 0: 3 components
|
|
* Component 0: Y(10)
|
|
* Component 1: Cb(10, 2x2 subsampled)
|
|
* Component 2: Cr(10, 2x2 subsampled)
|
|
|
|
* - DRM_FORMAT_NV12
|
|
- 8-bit per component YCbCr 420, two plane
|
|
- Plane 0: 1 component
|
|
* Component 0: Y(8)
|
|
Plane 1: 2 components
|
|
* Component 0: Cb(8, 2x2 subsampled)
|
|
* Component 1: Cr(8, 2x2 subsampled)
|
|
|
|
* - DRM_FORMAT_P010
|
|
- 10-bit per component YCbCr 420, two plane
|
|
- Plane 0: 1 component
|
|
* Component 0: Y(10)
|
|
Plane 1: 2 components
|
|
* Component 0: Cb(10, 2x2 subsampled)
|
|
* Component 1: Cr(10, 2x2 subsampled)
|