Hi Christoph, On Thu, Jul 25, 2019 at 8:35 AM Christoph Hellwig <hch@xxxxxx> 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? https://lore.kernel.org/linux-renesas-soc/CAMuHMdWkQ918Y61tMJbHEu29AGLEyNwbvZbSBB-RRH7YYUNRcA@xxxxxxxxxxxxxx/ Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx 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
