Re: [PATCH v2 2/7] dma: Introduce dma_aligned_pow2_mask()

[Peter Maydell]

On Thu, 25 Feb 2021 at 09:15, Eric Auger <eric.auger@redhat.com> wrote:
>
> Currently get_naturally_aligned_size() is used by the intel iommu
> to compute the maximum invalidation range based on @size which is
> a power of 2 while being aligned with the @start address and less
> than the maximum range defined by @gaw.
>
> This helper is also useful for other iommu devices (virtio-iommu,
> SMMUv3) to make sure IOMMU UNMAP notifiers only are called with
> power of 2 range sizes.
>
> Let's move this latter into dma-helpers.c and rename it into
> dma_aligned_pow2_mask(). Also rewrite the helper so that it
> accomodates UINT64_MAX values for the size mask and max mask.
> It now returns a mask instead of a size. Change the caller.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> diff --git a/include/sysemu/dma.h b/include/sysemu/dma.h
> index a052f7bca3..2acb303be2 100644
> --- a/include/sysemu/dma.h
> +++ b/include/sysemu/dma.h
> @@ -296,4 +296,7 @@ uint64_t dma_buf_write(uint8_t *ptr, int32_t len, 
> QEMUSGList *sg);
>  void dma_acct_start(BlockBackend *blk, BlockAcctCookie *cookie,
>                      QEMUSGList *sg, enum BlockAcctType type);
>
> +uint64_t dma_aligned_pow2_mask(uint64_t start, uint64_t end,
> +                               int max_addr_bits);

All new globally-visible functions in header files should have
a doc-comment describing what they do, please.

thanks
-- PMM