From: Adrian Larumbe <adrianml@alumnos.upm.es>
To: vkoul@kernel.org, dmaengine@vger.kernel.org
Cc: michal.simek@xilinx.com, linux-arm-kernel@lists.infradead.org,
Adrian Larumbe <adrianml@alumnos.upm.es>
Subject: [PATCH 1/3] dmaengine: Add documentation for new memcpy scatter-gather function
Date: Mon, 1 Nov 2021 18:08:23 +0000 [thread overview]
Message-ID: <20211101180825.241048-2-adrianml@alumnos.upm.es> (raw)
In-Reply-To: <20211101180825.241048-1-adrianml@alumnos.upm.es>
Documentation describes semantics, limitations and a typical use case
scenario.
Signed-off-by: Adrian Larumbe <adrianml@alumnos.upm.es>
---
.../driver-api/dmaengine/provider.rst | 23 +++++++++++++++++++
1 file changed, 23 insertions(+)
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
--
2.33.1
next prev parent reply other threads:[~2021-11-01 18:31 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-06 23:43 [PATCH 0/2] Add support for MEMCPY_SG transfers Adrian Larumbe
2021-07-06 23:43 ` [PATCH 1/2] dmaengine: xilinx_dma: Restore support for memcpy SG transfers Adrian Larumbe
2021-07-14 4:58 ` Vinod Koul
2021-07-26 22:14 ` Adrian Larumbe
2021-07-29 4:19 ` Vinod Koul
2021-07-06 23:43 ` [PATCH 2/2] xilinx_dma: Fix read-after-free bug when terminating transfers Adrian Larumbe
2021-07-14 5:10 ` Vinod Koul
2021-11-01 18:08 ` [PATCH 0/3] Add support for MEMCPY_SG transfers Adrian Larumbe
2021-11-01 18:08 ` Adrian Larumbe [this message]
2021-11-01 18:08 ` [PATCH 2/3] dmaengine: Add core function and capability check for DMA_MEMCPY_SG Adrian Larumbe
2021-11-01 18:08 ` [PATCH 3/3] dmaengine: Add consumer for the new DMA_MEMCPY_SG API function Adrian Larumbe
2021-11-02 10:33 ` [PATCH 0/3] Add support for MEMCPY_SG transfers Michal Simek
2021-11-22 6:08 ` Vinod Koul
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