diff options
| author | Adrian Larumbe <adrianml@alumnos.upm.es> | 2021-11-01 18:08:23 +0000 |
|---|---|---|
| committer | Vinod Koul <vkoul@kernel.org> | 2021-11-22 11:38:04 +0530 |
| commit | 58fe107660483138a7a77acd673b911016e4ad31 (patch) | |
| tree | f7262edb53d199cad66eafd28186aae07edb28d5 | |
| parent | 56fc39f5a36794c4f27f5fee047b641eac3f5b89 (diff) | |
dmaengine: Add documentation for new memcpy scatter-gather function
Documentation describes semantics, limitations and a typical use case
scenario.
Signed-off-by: Adrian Larumbe <adrianml@alumnos.upm.es>
Link: https://lore.kernel.org/r/20211101180825.241048-2-adrianml@alumnos.upm.es
Signed-off-by: Vinod Koul <vkoul@kernel.org>
| -rw-r--r-- | Documentation/driver-api/dmaengine/provider.rst | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/Documentation/driver-api/dmaengine/provider.rst b/Documentation/driver-api/dmaengine/provider.rst index ddb0a81a796c..0072c9c7efd3 100644 --- a/Documentation/driver-api/dmaengine/provider.rst +++ b/Documentation/driver-api/dmaengine/provider.rst @@ -162,6 +162,29 @@ Currently, the types available are: - The device is able to do memory to memory copies +- - DMA_MEMCPY_SG + + - The device supports memory to memory scatter-gather transfers. + + - Even though a plain memcpy can look like a particular case of a + scatter-gather transfer, with a single chunk to copy, it's a distinct + transaction type in the mem2mem transfer case. This is because some very + simple devices might be able to do contiguous single-chunk memory copies, + but have no support for more complex SG transfers. + + - No matter what the overall size of the combined chunks for source and + destination is, only as many bytes as the smallest of the two will be + transmitted. That means the number and size of the scatter-gather buffers in + both lists need not be the same, and that the operation functionally is + equivalent to a ``strncpy`` where the ``count`` argument equals the smallest + total size of the two scatter-gather list buffers. + + - It's usually used for copying pixel data between host memory and + memory-mapped GPU device memory, such as found on modern PCI video graphics + cards. The most immediate example is the OpenGL API function + ``glReadPielx()``, which might require a verbatim copy of a huge framebuffer + from local device memory onto host memory. + - DMA_XOR - The device is able to perform XOR operations on memory areas |