[PATCH 4/5] dma-mapping: provide a better default ->get_required_mask

Geert Uytterhoeven geert at linux-m68k.org
Mon Jul 29 19:57:19 AEST 2019

Hi Christoph,

On Thu, Jul 25, 2019 at 8:35 AM Christoph Hellwig <hch at lst.de> wrote:
> Most dma_map_ops instances are IOMMUs that work perfectly fine in 32-bits
> of IOVA space, and the generic direct mapping code already provides its
> own routines that is intelligent based on the amount of memory actually
> present.  Wire up the dma-direct routine for the ARM direct mapping code
> as well, and otherwise default to the constant 32-bit mask.  This way
> we only need to override it for the occasional odd IOMMU that requires
> 64-bit IOVA support, or IOMMU drivers that are more efficient if they
> can fall back to the direct mapping.

As I know you like diving into cans of worms ;-)

Does 64-bit IOVA support actually work in general? Or only on 64-bit
platforms, due to dma_addr_t to unsigned long truncation on 32-bit?




Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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