[PATCH v6.1] iommu/dma: Add support for mapping MSIs

On Wed, 7 Sep 2016, Robin Murphy wrote:

- Rework map_page() helper function plus insane lookup logic into
  straightforward get_page() helper
- Use phys_addr_t to further simplify address matching
- Fix the bit where I neglected to actually round the doorbell
  address to a page boundary (oops!)
- Make the locking hardirq-safe to satisfy lockdep

That looks way better.

Acked-by: Thomas Gleixner <redacted>