Re: [PATCH 0/9] dmaengine: Support bus widths of 32 bytes and above

On Thu, Jul 30, 2026 at 03:23:07PM +0100, Nuno Sá via B4 Relay wrote:
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>
> The DMA engine slave capabilities advertise the supported source and
> destination bus widths through src_addr_widths / dst_addr_widths. These
> are plain u32 bitmasks where a set bit's position equals the
> corresponding enum dma_slave_buswidth value, e.g.
> DMA_SLAVE_BUSWIDTH_4_BYTES sets bit 4.
>
> The consequence is that widths of 32 bytes and above cannot be
> represented at all: DMA_SLAVE_BUSWIDTH_32/64/128_BYTES would need bits
> 32, 64 and 128, which do not fit in a u32. Hardware with wider data
> paths is becoming common, so add a representation that can express these
> widths while still using enum dma_slave_buswidth.
>
> This series switches consumers and a small set of producers to bitmap
> based bus width capabilities. The legacy dma_device u32 fields are kept
> for now so the remaining DMA controller drivers can be converted
> incrementally. dma_get_slave_caps() folds legacy producer masks into the
> new bitmap representation returned to consumers.
>
> Once the remaining producers are converted, the legacy dma_device
> src/dst_addr_widths fields can be removed as a final cleanup.
>
> This issue was discussed before here:
>
> https://lore.kernel.org/dmaengine/abkoXXbaxaiqbBuX@vaman/
>
> ---
> Changes in v1:

this should be v2, RFC is v1

Frank
> - Drop RFC tag.
> - Rename the new capability representation and helpers from address
>   width terminology to bus width terminology.
> - Convert all current dma_get_slave_caps() consumers that used the
>   legacy src/dst_addr_widths fields.
> - Convert a small set of DMA controller producers and the stm32-dma3
>   per-channel capability callback.
> - Add helper documentation for the new public API.
> - Link to RFC: https://lore.kernel.org/dmaengine/20260616-dmaengine-support-wider-dma-masks-v1-0-da23a8dcb756@analog.com/
>
> ---
> Nuno Sá (9):
>       dmaengine: Support bus widths of 32 bytes and above
>       dmaengine: dma-axi-dmac: Use bus width capability helpers
>       dmaengine: dw-axi-dmac: Use bus width capability helpers
>       dmaengine: qcom: gpi: Use bus width capability helpers
>       dmaengine: stm32-dma3: Use bus width capability helpers
>       iio: buffer-dmaengine: Use dma_slave_caps bus width accessors
>       ALSA: pcm_dmaengine: Use dma_slave_caps bus width helpers
>       spi: dw: Use dma_slave_caps bus width helpers
>       dmaengine: Drop legacy bus width fields from dma_slave_caps
>
>  drivers/dma/dma-axi-dmac.c                         |  13 +-
>  drivers/dma/dmaengine.c                            |  20 +-
>  drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c     |  39 ++--
>  drivers/dma/qcom/gpi.c                             |  11 +-
>  drivers/dma/stm32/stm32-dma3.c                     |  32 +--
>  drivers/iio/buffer/industrialio-buffer-dmaengine.c |  15 +-
>  drivers/spi/spi-dw-dma.c                           |   6 +-
>  drivers/spi/spi-dw.h                               |   3 +-
>  include/linux/dmaengine.h                          | 234 ++++++++++++++++++++-
>  sound/core/pcm_dmaengine.c                         |  14 +-
>  10 files changed, 323 insertions(+), 64 deletions(-)
> ---
> base-commit: 7524fe142b5a772f8421aeee2132cf7e21a00103
> change-id: 20260615-dmaengine-support-wider-dma-masks-5aac12497e27
> --
>
> Thanks!
> - Nuno Sá
>
>