Re: [PATCH RFC 1/3] dmaengine: Support address bus widths of 32 bytes and above

["Nuno Sá" <noname.nuno@gmail.com>]

On Tue, Jun 16, 2026 at 11:19:51AM -0500, Frank Li wrote:
> On Tue, Jun 16, 2026 at 04:40:52PM +0100, Nuno Sá via B4 Relay wrote:
> > [You don't often get email from devnull+nuno.sa.analog.com@kernel.org. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> >
> > From: Nuno Sá <nuno.sa@analog.com>
> >
> > 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.
> 
> This is problem, which should be fixed.
> 
> >
> > Introduce bitmap-based masks that span the full enum range. To allow
> > controllers and consumers to be converted incrementally, the legacy
> > u32 fields are kept alongside the new bitmaps: producers populate the
> > bitmap (mirroring the low 32 bits back into the legacy field) and
> > dma_get_slave_caps() folds a legacy-only producer's u32 into the
> > returned bitmap.
> >
> > Add dma_set_{src,dst}_addr_mask() for producers and
> > dma_slave_caps_get_{src,dst}_width_min() for consumers so that, once
> > every user is converted, the legacy u32 fields can be dropped and the
> > bitmaps renamed without further churn.
> 
> Good mirgration plan.

Cool! I'll then wait some more days and if nothing pops up will drop the
RFC and send a new series addressing some valid AI inputs and converting
more drivers.

- Nuno Sá
> 
> Frank