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 the new
bus width capabilities, represented by a dma_buswidth_mask_t modeled
after dma_cap_mask_t. The legacy dma_device u32 fields are kept for now
so the remaining DMA controller drivers can be converted incrementally:
dma_async_device_register() folds a legacy-only producer's u32 into the
mask, so consumers only ever have to look at the mask.
The new interface lives in include/linux/dma/engine/{types,widthmask}.h
rather than in linux/dmaengine.h, so that only its users pay for the
linux/bitmap.h include. Every accessor takes a dma_buswidth_mask_t,
which means the interface will not change when the legacy fields are
eventually dropped.
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 v3:
- Patch 1:
- Move the new interface out of linux/dmaengine.h into two new headers,
include/linux/dma/engine/types.h (enum dma_slave_buswidth and the new
dma_buswidth_mask_t) and include/linux/dma/engine/widthmask.h (the
accessors). Only the latter includes linux/bitmap.h and it is not
included back into linux/dmaengine.h (Andy).
- Replace the raw bitmap with a dma_buswidth_mask_t type modeled after
dma_cap_mask_t, so linux/dmaengine.h does not need linux/bitmap.h for
the struct members.
- Every accessor now takes a dma_buswidth_mask_t instead of a
struct dma_device / struct dma_slave_caps, so the interface stays the
same once the legacy fields are dropped. Consequently
dma_slave_caps_{get,copy,intersect,clear}_*_width() are gone.
- Fold the legacy producer masks once in dma_async_device_register()
instead of on every dma_get_slave_caps() call. On top of that, only
when a device_caps() callback adjusted the masks, derive the legacy
dma_slave_caps masks from them, so that a converted controller driver
is also seen by the consumers not converted yet, while a driver still
adjusting the legacy masks directly keeps working.
- Patch 5:
- Also convert the driver's own read of the legacy capabilities in
stm32_dma3_chan_prep_hw(); besides completing the conversion this
stops BIT() from being fed an unvalidated device tree bus width.
- Drop the stm32_dma3 prefix from the local buswidths[] array and move
it below the struct declarations (Amelie).
- Link to v2: https://patch.msgid.link/20260810-dmaengine-support-wider-dma-masks-v2-0-1f7b798d035f@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
MAINTAINERS | 1 +
drivers/dma/dma-axi-dmac.c | 14 +-
drivers/dma/dmaengine.c | 27 +++-
drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c | 38 +++--
drivers/dma/qcom/gpi.c | 12 +-
drivers/dma/stm32/stm32-dma3.c | 34 +++--
drivers/iio/buffer/industrialio-buffer-dmaengine.c | 16 +-
drivers/spi/spi-dw-dma.c | 8 +-
drivers/spi/spi-dw.h | 3 +-
include/linux/dma/engine/types.h | 41 ++++++
include/linux/dma/engine/widthmask.h | 164 +++++++++++++++++++++
include/linux/dmaengine.h | 47 +++---
sound/core/pcm_dmaengine.c | 21 ++-
13 files changed, 342 insertions(+), 84 deletions(-)
---
base-commit: 0613e7934ee233d726af8d8c89f251a1c4df738d
change-id: 20260615-dmaengine-support-wider-dma-masks-5aac12497e27
--
Thanks!
- Nuno Sá