RE: [PATCH v2 1/1] swiotlb: Reduce swiotlb pool lookups

[Michael Kelley <mhklinux@xxxxxxxxxxx>]

From: Michael Kelley Sent: Saturday, July 6, 2024 7:12 PM

[ ... ]
> >
> > If we then stub out swiotlb_find_pool to return NULL for !CONFIG_SWIOTLB,
> > we also don't need extra stubs for all the __swiotlb_ helpers as the
> > compiler will eliminate the calls as dead code.
> 
> Yes, this works as long as the declarations for the __swiotlb_foo
> functions are *not* under CONFIG_SWIOTLB. But when compiling with
> !CONFIG_SWIOTLB on arm64 with gcc-8.5.0, two tangentially related
> compile errors occur. iommu_dma_map_page() references
> swiotlb_tlb_map_single(). The declaration for the latter is under
> CONFIG_SWIOTLB. A similar problem occurs with dma_direct_map_page()
> and swiotlb_map(). Do later versions of gcc not complain when the
> reference is in dead code? Or are these just bugs that occurred because
> !CONFIG_SWIOTLB is rare? If the latter, I can submit a separate patch to
> move the declarations out from under CONFIG_SWIOTLB.
> 

Ignore the "two tangentially related compile errors".  I schlepped some
code around incorrectly and caused the problem myself. :-(

Michael