On Tue, 07 Oct 2025 10:15:20 +0100 Nuno Sá via B4 Relay devnull+nuno.sa.analog.com@kernel.org wrote:
This series fixes an issue with DMABUF support in the IIO subsystem where the wrong DMA device could be used for buffer mapping operations. This becomes critical on systems like Xilinx/AMD ZynqMP Ultrascale where memory can be mapped above the 32-bit address range.
Problem:
The current IIO DMABUF implementation assumes it can use the parent device of the IIO device for DMA operations. However, this device may not have the appropriate DMA mask configuration for accessing high memory addresses. On systems where memory is mapped above 32-bits, this leads to the use of bounce buffers through swiotlb, significantly impacting performance.
Solution:
This series introduces a new .get_dma_dev() callback in the buffer access functions that allows buffer implementations to specify the correct DMA device that should be used for DMABUF operations. The DMA buffer infrastructure implements this callback to return the device that actually owns the DMA channel, ensuring proper memory mapping without bounce buffers.
Changes:
- Add .get_dma_dev() callback to iio_buffer_access_funcs and update core DMABUF code to use it when available
- Implement the callback in the DMA buffer infrastructure
- Wire up the callback in the dmaengine buffer implementation
This ensures that DMABUF operations use the device with the correct DMA configuration, eliminating unnecessary bounce buffer usage and improving performance on high-memory systems.
(AI generated cover. I would not be this formal but I guess is not that bad :))
Changes in v3:
- Patch 1
- Add a new iio_buffer_get_dma_dev() helper to get the DMA dev.
- Link to v2: https://lore.kernel.org/r/20251006-fix-iio-dmabuf-get-dma-device-v2-0-d960bc...
Looks like I misinterpreted outcome of v2 thread. Anyhow dropped that and picked this up.
Thanks
J
Nuno Sá (3): iio: buffer: support getting dma channel from the buffer iio: buffer-dma: support getting the DMA channel iio: buffer-dmaengine: enable .get_dma_dev()
drivers/iio/buffer/industrialio-buffer-dma.c | 6 ++++++ drivers/iio/buffer/industrialio-buffer-dmaengine.c | 2 ++ drivers/iio/industrialio-buffer.c | 21 ++++++++++++++++----- include/linux/iio/buffer-dma.h | 1 + include/linux/iio/buffer_impl.h | 2 ++ 5 files changed, 27 insertions(+), 5 deletions(-)
base-commit: b9700f87939f0f477e5c00db817f54ab8a97702b change-id: 20250930-fix-iio-dmabuf-get-dma-device-339ac70543db --
Thanks!
- Nuno Sá