Re: [PATCH 2/5] rust: dma: add DMA addressing capabilities

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jul 10, 2025 at 09:45:44PM +0200, Danilo Krummrich wrote:
> +/// Returns a bitmask with the lowest `n` bits set to `1`.
> +///
> +/// For `n` in `0..=64`, returns a mask with the lowest `n` bits set.
> +/// For `n > 64`, returns `u64::MAX` (all bits set).
> +///
> +/// # Examples
> +///
> +/// ```
> +/// use kernel::dma::dma_bit_mask;
> +///
> +/// assert_eq!(dma_bit_mask(0), 0);
> +/// assert_eq!(dma_bit_mask(1), 0b1);
> +/// assert_eq!(dma_bit_mask(64), u64::MAX);
> +/// assert_eq!(dma_bit_mask(100), u64::MAX); // Saturates at all bits set.
> +/// ```
> +pub const fn dma_bit_mask(n: usize) -> u64 {
> +    match n {
> +        0 => 0,
> +        1..=64 => u64::MAX >> (64 - n),
> +        _ => u64::MAX,
> +    }
> +}

This is just the C macro DMA_BIT_MASK(), right?  If so, can that be said
here somewhere?  Or, how about turning DMA_BIT_MASK() into an inline
function which could then be just called by the rust code directly
instead?

Just a minor thing, but it stood out to me here.

thanks,

greg k-h