On Mon, Aug 06, 2018 at 12:01:34PM +0200, Arnd Bergmann wrote: > There are a few subtle corner cases here, in particular in which cases > the new dma_set_mask() behavior on arm64 reports success or > failure when truncating the mask to the bus_dma_mask.
Going forward my plan was to make dma_set_mask() never fail. The idea is that it sets the mask that the device is capable of, and the core dma code is responsible for also looking at bus_dma_mask and otherwise make things just work. Robin brought up the case where a platform can't handle a given limitation ever, e.g. a PCI(e) device with a 24-bit dma mask on a device with a dma offset that means we'll never have any physical memory reachable in that range. So we'll either still need to allow it to fail for such corner cases or delay such error until later, e.g. when dma_alloc_* (or in the corner case of the corner case dma_map_*) is called. I'm still undecided which way to go, but not allowing error returns from dma_set_mask and its variants sounds very tempting. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
