On Wed, 7 May 2025, Christoph Hellwig wrote: > On Wed, May 07, 2025 at 04:09:15PM -0700, Stefano Stabellini wrote: > > > This mapping is not for a RAM backed address. In the eDMA case for the > > > iMX8QXP the `phys` coming in here is the address of a register. > > > > Ok, this information is important :-) > > > > I am not certain whether the map_resource interface can only be called > > for MMIO addresses or if it can also be called for RAM-backed addresses > > with a size > PAGE_SIZE. In the latter case, we could run into the issue > > I was describing. > > map_resource is intended for MMIO regions, although those could be > > PAGE_SIZE. It must not be called on RAM.
In that case, John, you can just use dma_direct_map_resource(). That's because MMIO regions: - are 1:1 mapped on ARM - are 1:1 mapped on x86 for PV Dom0 - might not be 1:1 mapped on x86 for PVH Dom0, but in this case we rely on the IOMMU to do address translation In none of these cases xen_phys_to_dma would give us any interesting results. It would be the same as calling phys_to_dma.
