[PATCH v9 07/24] dma-mapping: Implement link/unlink ranges API

[Christoph Hellwig]

On Sun, Apr 27, 2025 at 11:13:12AM +0300, Leon Romanovsky wrote:
> > So arch_sync_dma_for_device() is a no-op on some architectures, notably x86.
> > So since you're doing this work and given the above pattern is common on
> > the non iova case, we could save ourselves 2 branches checks on x86 on
> > __dma_iova_link() and also generalize savings for the non-iova case as
> > well. For the non-iova case we have two use cases, one with the attrs on
> > initial mapping, and one without on subsequent sync ops. For the iova
> > case the attr is always consistently used.
> 
> I want to believe that compiler will discards these "if (!coherent &&
> !(attrs & DMA_ATTR_SKIP_CPU_SYNC)))" branch if case is empty.

Yes, it is the poster child for dead code elimination using the
IS_ENABLED() helper.

> checks are scattered over all dma-iommu.c file with different
> combinations. While we can do new static functions for small number of
> use cases, it will be half-solution.

Don't bother.