Re: [PATCH 1/9] dmaengine: Support bus widths of 32 bytes and above

On Thu, 30 Jul 2026 14:16:30 -0500
Frank Li <[email protected]> wrote:

> On Thu, Jul 30, 2026 at 03:23:08PM +0100, Nuno S=C3=A1 via B4 Relay wrote:
> > [You don't often get email from [email protected]. =
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> >
> > From: Nuno S=C3=A1 <[email protected]>
> >
> > The src_addr_widths and dst_addr_widths capability masks encode each
> > supported width as a bit whose position equals the corresponding
> > enum dma_slave_buswidth value (e.g. DMA_SLAVE_BUSWIDTH_4_BYTES sets bit
> > 4). As these masks are plain u32, widths of 32 bytes and above
> > (DMA_SLAVE_BUSWIDTH_32/64/128_BYTES map to bits 32, 64 and 128) cannot
> > be represented at all.
> >
> > Introduce bitmap-based bus width capabilities that span the full enum
> > range. To allow DMA controller producers to be converted incrementally,
> > keep the legacy dma_device u32 fields alongside the new bitmaps:
> > producers using the new helpers populate the bitmap and mirror the low
> > 32 bits back into the legacy field, while dma_get_slave_caps() folds a
> > legacy-only producer's u32 into the returned bitmap.
> >
> > Add helpers for producers and consumers so users do not need to depend
> > on the bitmap layout directly. Once the remaining producers are
> > converted, the legacy dma_device u32 fields can be dropped.
> >
> > Signed-off-by: Nuno S=C3=A1 <[email protected]>
> > --- =20
>=20
> Reviewed-by: Frank Li <[email protected]>
https://sashiko.dev/#/patchset/20260730-dmaengine-support-wider-dma-masks-v=
1-0-3732f1f9d9ca%40analog.com=20
has a comment on this that smells plausible at least.
Looks like the stm32 driver modifies dst_bus_widths in it's device_caps()
callback.

Jonathan