Re: [PATCH v5 1/9] dmaengine: Support bus widths of 32 bytes and above

[Frank Li]

On Fri, Oct 09, 2026 at 04:52:53PM +0100, Nuno Sá wrote:
> 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, through a new dma_buswidth_mask_t type modeled after
> dma_cap_mask_t. To allow DMA controller drivers to be converted
> incrementally, the legacy dma_device u32 fields are kept alongside the
> new masks and the core folds a legacy-only driver's u32 into the mask
> when the device is registered, so consumers only ever have to look at
> the mask.
>
> The fold is bidirectional while both representations coexist. A driver
> that only fills in the legacy u32 gets its mask derived from it, so the
> consumers already converted see it. A driver that only fills in the mask
> gets its legacy u32 derived from the mask, so the consumers not
> converted yet, which read the legacy dma_slave_caps fields, keep working.
>
> On top of that, dma_get_slave_caps() derives the legacy dma_slave_caps
> masks from the new ones when a device_caps() callback adjusted them, so
> that a converted controller narrowing its per-channel capabilities is
> still seen by the consumers not converted yet, while a driver adjusting
> the legacy masks directly keeps working.
>
> Signed-off-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
>
> ---
>
> Andy, did not take your tag given that you're the one asking for the
> split and since we ended up not doing it, not sure if the tag is
> to be kept :)
> ---
>  drivers/dma/dmaengine.c   |  51 +++++++++++-
>  include/linux/dmaengine.h | 208 +++++++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 246 insertions(+), 13 deletions(-)
>
...
>
>  	/* note: this only matters in the
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 71cde09ff240..eb68eea840b5 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -427,8 +427,179 @@ enum dma_slave_buswidth {
>  	DMA_SLAVE_BUSWIDTH_32_BYTES = 32,
>  	DMA_SLAVE_BUSWIDTH_64_BYTES = 64,
>  	DMA_SLAVE_BUSWIDTH_128_BYTES = 128,
> +	DMA_SLAVE_BUSWIDTH_MAX
>  };
>
...
> +/**
> + * dma_bus_width_min - get the smallest bus width of a bus width mask
> + * @mask: bus width mask
> + *
> + * Return: the smallest bus width set in @mask, or
> + * %DMA_SLAVE_BUSWIDTH_UNDEFINED if @mask is empty.
> + */
> +#define dma_bus_width_min(mask) __dma_bus_width_min(&(mask))
> +

We are working on make dma_device private. New API avoid direct use
dma_device field.

pass down dma_chan point, dma engine handle everything in core part.

> +static inline void __dma_bus_width_copy(dma_buswidth_mask_t *dst,
> +					const dma_buswidth_mask_t *src)
> +{
> +	bitmap_copy(dst->bits, src->bits, DMA_SLAVE_BUSWIDTH_MAX);
> +}
> +
> +/**
> + * dma_bus_width_copy - copy a bus width mask
> + * @dst: bus width mask to copy to
> + * @src: bus width mask to copy from
> + */
> +#define dma_bus_width_copy(dst, src) __dma_bus_width_copy(&(dst), &(src))
> +
> +static inline bool __dma_bus_width_and(dma_buswidth_mask_t *dst,
> +				       const dma_buswidth_mask_t *src1,
> +				       const dma_buswidth_mask_t *src2)
> +{
> +	return bitmap_and(dst->bits, src1->bits, src2->bits,
> +			  DMA_SLAVE_BUSWIDTH_MAX);
> +}
> +
> +/**
> + * dma_bus_width_and - intersect two bus width masks
> + * @dst: bus width mask to store the result in
> + * @src1: first bus width mask
> + * @src2: second bus width mask
> + *
> + * Return: true if @dst has at least one bus width set, false otherwise.
> + */
> +#define dma_bus_width_and(dst, src1, src2) \
> +	__dma_bus_width_and(&(dst), &(src1), &(src2))
> +

One thing I forget, new API should start from dmaengine_.

Frank