On Mon, Aug 31, 2026 at 04:50:33PM +0300, Andy Shevchenko wrote:
On Mon, Aug 31, 2026 at 12:46:37PM +0100, Nuno Sá wrote:
quoted
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/ (local)
Thanks, this version looks like the right approach. I have looked at a couple
of patches and only the first one needs a bit of work, the rest looks nice!
It does! Once this lands, I do intend to do the same separation for the
caps_mask so that we can drop bitmap from dmaengine.h
- Nuno Sá
--
With Best Regards,
Andy Shevchenko