| .. 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) |