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

On Thu, Jul 30, 2026 at 03:23:08PM +0100, Nuno Sá via B4 Relay wrote:
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>
> From: Nuno Sá <[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 Sá <[email protected]>
> ---

Reviewed-by: Frank Li <[email protected]>

>  drivers/dma/dmaengine.c   |  18 ++++
>  include/linux/dmaengine.h | 246 ++++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 254 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 9049171df857..7be23ba769d0 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -593,7 +593,25 @@ int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
>                 return -ENXIO;
>
>         caps->src_addr_widths = device->src_addr_widths;
> +       if (bitmap_empty(device->src_bus_widths, DMA_SLAVE_BUSWIDTH_MAX)) {
> +               bitmap_zero(caps->src_bus_widths, DMA_SLAVE_BUSWIDTH_MAX);
> +               bitmap_from_arr32(caps->src_bus_widths,
> +                                 &device->src_addr_widths, 32);
> +       } else {
> +               bitmap_copy(caps->src_bus_widths, device->src_bus_widths,
> +                           DMA_SLAVE_BUSWIDTH_MAX);
> +       }
> +
>         caps->dst_addr_widths = device->dst_addr_widths;
> +       if (bitmap_empty(device->dst_bus_widths, DMA_SLAVE_BUSWIDTH_MAX)) {
> +               bitmap_zero(caps->dst_bus_widths, DMA_SLAVE_BUSWIDTH_MAX);
> +               bitmap_from_arr32(caps->dst_bus_widths,
> +                                 &device->dst_addr_widths, 32);
> +       } else {
> +               bitmap_copy(caps->dst_bus_widths, device->dst_bus_widths,
> +                           DMA_SLAVE_BUSWIDTH_MAX);
> +       }
> +
>         caps->directions = device->directions;
>         caps->min_burst = device->min_burst;
>         caps->max_burst = device->max_burst;
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index b3d251c9734e..cea57b166dcb 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -5,6 +5,7 @@
>  #ifndef LINUX_DMAENGINE_H
>  #define LINUX_DMAENGINE_H
>
> +#include <linux/bitops.h>
>  #include <linux/device.h>
>  #include <linux/err.h>
>  #include <linux/uio.h>
> @@ -391,8 +392,12 @@ 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
>  };
>
> +#define DECLARE_DMA_BUS_WIDTHS(name) \
> +       DECLARE_BITMAP(name, DMA_SLAVE_BUSWIDTH_MAX)
> +
>  /**
>   * struct dma_slave_config - dma slave channel runtime config
>   * @direction: whether the data shall go in or out on this slave
> @@ -487,10 +492,12 @@ enum dma_residue_granularity {
>
>  /**
>   * struct dma_slave_caps - expose capabilities of a slave channel only
> - * @src_addr_widths: bit mask of src addr widths the channel supports.
> + * @src_bus_widths: bitmap of source bus widths the channel supports.
>   *     Width is specified in bytes, e.g. for a channel supporting
> - *     a width of 4 the mask should have BIT(4) set.
> - * @dst_addr_widths: bit mask of dst addr widths the channel supports
> + *     a width of 4 the bitmap should have bit 4 set.
> + * @src_addr_widths: legacy bit mask of source bus widths the channel supports.
> + * @dst_bus_widths: bitmap of destination bus widths the channel supports.
> + * @dst_addr_widths: legacy bit mask of destination bus widths the channel supports.
>   * @directions: bit mask of slave directions the channel supports.
>   *     Since the enum dma_transfer_direction is not defined as bit flag for
>   *     each type, the dma controller should set BIT(<TYPE>) and same
> @@ -509,8 +516,14 @@ enum dma_residue_granularity {
>   * resubmitted multiple times
>   */
>  struct dma_slave_caps {
> -       u32 src_addr_widths;
> -       u32 dst_addr_widths;
> +       struct {
> +               DECLARE_DMA_BUS_WIDTHS(src_bus_widths);
> +               u32 src_addr_widths;
> +       };
> +       struct {
> +               DECLARE_DMA_BUS_WIDTHS(dst_bus_widths);
> +               u32 dst_addr_widths;
> +       };
>         u32 directions;
>         u32 min_burst;
>         u32 max_burst;
> @@ -803,10 +816,12 @@ struct dma_filter {
>   * @dev: struct device reference for dma mapping api
>   * @owner: owner module (automatically set based on the provided dev)
>   * @chan_ida: unique channel ID
> - * @src_addr_widths: bit mask of src addr widths the device supports
> + * @src_bus_widths: bitmap of source bus widths the device supports.
>   *     Width is specified in bytes, e.g. for a device supporting
> - *     a width of 4 the mask should have BIT(4) set.
> - * @dst_addr_widths: bit mask of dst addr widths the device supports
> + *     a width of 4 the bitmap should have bit 4 set.
> + * @src_addr_widths: legacy bit mask of source bus widths the device supports.
> + * @dst_bus_widths: bitmap of destination bus widths the device supports.
> + * @dst_addr_widths: legacy bit mask of destination bus widths the device supports.
>   * @directions: bit mask of slave directions the device supports.
>   *     Since the enum dma_transfer_direction is not defined as bit flag for
>   *     each type, the dma controller should set BIT(<TYPE>) and same
> @@ -887,8 +902,14 @@ struct dma_device {
>         struct module *owner;
>         struct ida chan_ida;
>
> -       u32 src_addr_widths;
> -       u32 dst_addr_widths;
> +       struct {
> +               DECLARE_DMA_BUS_WIDTHS(src_bus_widths);
> +               u32 src_addr_widths;
> +       };
> +       struct {
> +               DECLARE_DMA_BUS_WIDTHS(dst_bus_widths);
> +               u32 dst_addr_widths;
> +       };
>         u32 directions;
>         u32 min_burst;
>         u32 max_burst;
> @@ -1678,4 +1699,209 @@ static inline struct device *dmaengine_get_dma_device(struct dma_chan *chan)
>         return chan->device->dev;
>  }
>
> +static inline enum dma_slave_buswidth
> +__dma_slave_caps_get_width_min(const unsigned long *bus_widths)
> +{
> +       enum dma_slave_buswidth width = find_first_bit(bus_widths,
> +                                                      DMA_SLAVE_BUSWIDTH_MAX);
> +
> +       if (width == DMA_SLAVE_BUSWIDTH_MAX)
> +               return DMA_SLAVE_BUSWIDTH_UNDEFINED;
> +
> +       return width;
> +}
> +
> +/**
> + * dma_slave_caps_get_src_width_min - get the minimum source bus width
> + * @caps: DMA slave capabilities
> + *
> + * Return: the minimum supported source bus width, or
> + * %DMA_SLAVE_BUSWIDTH_UNDEFINED if no source bus width is advertised.
> + */
> +static inline enum dma_slave_buswidth
> +dma_slave_caps_get_src_width_min(const struct dma_slave_caps *caps)
> +{
> +       return __dma_slave_caps_get_width_min(caps->src_bus_widths);
> +}
> +
> +/**
> + * dma_slave_caps_get_dst_width_min - get the minimum destination bus width
> + * @caps: DMA slave capabilities
> + *
> + * Return: the minimum supported destination bus width, or
> + * %DMA_SLAVE_BUSWIDTH_UNDEFINED if no destination bus width is advertised.
> + */
> +static inline enum dma_slave_buswidth
> +dma_slave_caps_get_dst_width_min(const struct dma_slave_caps *caps)
> +{
> +       return __dma_slave_caps_get_width_min(caps->dst_bus_widths);
> +}
> +
> +/**
> + * dma_slave_caps_copy_src_widths - copy source bus width capabilities
> + * @caps: DMA slave capabilities
> + * @bus_widths: destination bitmap declared with DECLARE_DMA_BUS_WIDTHS()
> + */
> +static inline void
> +dma_slave_caps_copy_src_widths(const struct dma_slave_caps *caps,
> +                              unsigned long *bus_widths)
> +{
> +       bitmap_copy(bus_widths, caps->src_bus_widths, DMA_SLAVE_BUSWIDTH_MAX);
> +}
> +
> +/**
> + * dma_slave_caps_copy_dst_widths - copy destination bus width capabilities
> + * @caps: DMA slave capabilities
> + * @bus_widths: destination bitmap declared with DECLARE_DMA_BUS_WIDTHS()
> + */
> +static inline void
> +dma_slave_caps_copy_dst_widths(const struct dma_slave_caps *caps,
> +                              unsigned long *bus_widths)
> +{
> +       bitmap_copy(bus_widths, caps->dst_bus_widths, DMA_SLAVE_BUSWIDTH_MAX);
> +}
> +
> +/**
> + * dma_slave_caps_intersect_widths - intersect destination and source widths
> + * @dst_caps: DMA slave capabilities providing destination bus widths
> + * @src_caps: DMA slave capabilities providing source bus widths
> + * @bus_widths: destination bitmap declared with DECLARE_DMA_BUS_WIDTHS()
> + *
> + * Return: true if the resulting bitmap contains at least one common bus width,
> + * false otherwise.
> + */
> +static inline bool
> +dma_slave_caps_intersect_widths(const struct dma_slave_caps *dst_caps,
> +                               const struct dma_slave_caps *src_caps,
> +                               unsigned long *bus_widths)
> +{
> +       return bitmap_and(bus_widths, dst_caps->dst_bus_widths,
> +                         src_caps->src_bus_widths, DMA_SLAVE_BUSWIDTH_MAX);
> +}
> +
> +/**
> + * dma_slave_caps_clear_src_width - clear a source bus width capability
> + * @caps: DMA slave capabilities
> + * @width: source bus width to clear
> + */
> +static inline void
> +dma_slave_caps_clear_src_width(struct dma_slave_caps *caps,
> +                              enum dma_slave_buswidth width)
> +{
> +       __clear_bit(width, caps->src_bus_widths);
> +       if (width < DMA_SLAVE_BUSWIDTH_32_BYTES)
> +               caps->src_addr_widths &= ~BIT(width);
> +}
> +
> +/**
> + * dma_slave_caps_clear_dst_width - clear a destination bus width capability
> + * @caps: DMA slave capabilities
> + * @width: destination bus width to clear
> + */
> +static inline void
> +dma_slave_caps_clear_dst_width(struct dma_slave_caps *caps,
> +                              enum dma_slave_buswidth width)
> +{
> +       __clear_bit(width, caps->dst_bus_widths);
> +       if (width < DMA_SLAVE_BUSWIDTH_32_BYTES)
> +               caps->dst_addr_widths &= ~BIT(width);
> +}
> +
> +static inline int __dma_set_bus_widths(unsigned long *bus_widths,
> +                                      const enum dma_slave_buswidth *widths,
> +                                      unsigned int n_widths)
> +{
> +       for (unsigned int i = 0; i < n_widths; i++) {
> +               switch (widths[i]) {
> +               case DMA_SLAVE_BUSWIDTH_UNDEFINED:
> +               case DMA_SLAVE_BUSWIDTH_1_BYTE:
> +               case DMA_SLAVE_BUSWIDTH_2_BYTES:
> +               case DMA_SLAVE_BUSWIDTH_3_BYTES:
> +               case DMA_SLAVE_BUSWIDTH_4_BYTES:
> +               case DMA_SLAVE_BUSWIDTH_8_BYTES:
> +               case DMA_SLAVE_BUSWIDTH_16_BYTES:
> +               case DMA_SLAVE_BUSWIDTH_32_BYTES:
> +               case DMA_SLAVE_BUSWIDTH_64_BYTES:
> +               case DMA_SLAVE_BUSWIDTH_128_BYTES:
> +                       break;
> +               default:
> +                       return -EINVAL;
> +               }
> +
> +               __set_bit(widths[i], bus_widths);
> +       }
> +
> +       return 0;
> +}
> +
> +/**
> + * dma_set_src_bus_widths - set supported source bus widths for a DMA device
> + * @device: DMA device
> + * @widths: array of supported source bus widths
> + * @n_widths: number of entries in @widths
> + *
> + * Return: 0 on success, -EINVAL if @widths contains an invalid bus width.
> + */
> +static inline int dma_set_src_bus_widths(struct dma_device *device,
> +                                        const enum dma_slave_buswidth *widths,
> +                                        unsigned int n_widths)
> +{
> +       int ret;
> +
> +       ret = __dma_set_bus_widths(device->src_bus_widths, widths, n_widths);
> +       if (ret)
> +               return ret;
> +
> +       device->src_addr_widths = bitmap_read(device->src_bus_widths, 0, 32);
> +       return 0;
> +}
> +
> +/**
> + * dma_set_dst_bus_widths - set supported destination bus widths for a DMA device
> + * @device: DMA device
> + * @widths: array of supported destination bus widths
> + * @n_widths: number of entries in @widths
> + *
> + * Return: 0 on success, -EINVAL if @widths contains an invalid bus width.
> + */
> +static inline int dma_set_dst_bus_widths(struct dma_device *device,
> +                                        const enum dma_slave_buswidth *widths,
> +                                        unsigned int n_widths)
> +{
> +       int ret;
> +
> +       ret = __dma_set_bus_widths(device->dst_bus_widths, widths, n_widths);
> +       if (ret)
> +               return ret;
> +
> +       device->dst_addr_widths = bitmap_read(device->dst_bus_widths, 0, 32);
> +       return 0;
> +}
> +
> +/**
> + * dma_set_src_bus_width - set a single supported source bus width
> + * @device: DMA device
> + * @width: supported source bus width
> + *
> + * Return: 0 on success, -EINVAL if @width is invalid.
> + */
> +static inline int dma_set_src_bus_width(struct dma_device *device,
> +                                       enum dma_slave_buswidth width)
> +{
> +       return dma_set_src_bus_widths(device, &width, 1);
> +}
> +
> +/**
> + * dma_set_dst_bus_width - set a single supported destination bus width
> + * @device: DMA device
> + * @width: supported destination bus width
> + *
> + * Return: 0 on success, -EINVAL if @width is invalid.
> + */
> +static inline int dma_set_dst_bus_width(struct dma_device *device,
> +                                       enum dma_slave_buswidth width)
> +{
> +       return dma_set_dst_bus_widths(device, &width, 1);
> +}
> +
>  #endif /* DMAENGINE_H */
>
> --
> 2.55.0
>
>