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converts it to a physical address using page_to_phys() whilst your new
dma_map_phys() interface takes a physical address and converts it to
a 'struct page *' using phys_to_page(). In both cases, hmm_dma_map_pfn()
still needs the page for other reasons. If anything, existing users of
dma_map_page_attrs() now end up with a redundant page-to-phys-to-page
conversion which hopefully the compiler folds away.

I'm assuming there's future work which builds on top of the new API
and removes the reliance on 'struct page' entirely, is that right? If
so, it would've been nicer to be clearer about that as, on its own, I'm
not really sure this patch series achieves an awful lot and the
efficiency argument looks quite weak to me.

Cheers,

Will