Neil Armstrong [off-list ref] writes:

Amlogic uses a proprietary lossless image compression protocol and format
for their hardware video codec accelerators, either video decoders or
video input encoders.

It considerably reduces memory bandwidth while writing and reading
frames in memory.

The underlying storage is considered to be 3 components, 8bit or 10-bit
per component, YCbCr 420, single plane :
- DRM_FORMAT_YUV420_8BIT
- DRM_FORMAT_YUV420_10BIT

This modifier will be notably added to DMA-BUF frames imported from the V4L2
Amlogic VDEC decoder.

At least two layout are supported :
- Basic: composed of a body and a header
- Scatter: the buffer is filled with a IOMMU scatter table referring
  to the encoder current memory layout. This mode if more efficient in terms
  of memory allocation but frames are not dumpable and only valid during until
  the buffer is freed and back in control of the encoder

At least two options are supported :
- Memory saving: when the pixel bpp is 8b, the size of the superblock can
  be reduced, thus saving memory.

This serie adds the missing register, updated the FBC decoder registers
content to be committed by the crtc code.

The Amlogic FBC has been tested with compressed content from the Amlogic
HW VP9 decoder on S905X (GXL), S905D2 (G12A) and S905X3 (SM1) in 8bit
(Scatter+Mem Saving on G12A/SM1, Mem Saving on GXL) and 10bit
(Scatter on G12A/SM1, default on GXL).

Tested on meson-sm1-sei610 (VP9 60fps content).

Tested-by: Kevin Hilman <khilman@baylibre.com>

Kevin

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