| .. 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) |
