On Mon, Mar 23, 2020 at 12:28:34PM +1100, Alexey Kardashevskiy wrote: [full quote deleted, please follow proper quoting rules]
> > +static bool dma_alloc_direct(struct device *dev, const struct dma_map_ops > > *ops) > > +{ > > + if (!ops) > > + return true; > > + > > + /* > > + * Allows IOMMU drivers to bypass dynamic translations if the DMA mask > > + * is large enough. > > + */ > > + if (dev->dma_ops_bypass) { > > + if (min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit) >= > > + dma_direct_get_required_mask(dev)) > > + return true; > > + } > > > Why not do this in dma_map_direct() as well? Mostly beacuse it is a relatively expensive operation, including a fls64. > Or simply have just one dma_map_direct()? What do you mean with that? > And one more general question - we need a way to use non-direct IOMMU > for RAM above certain limit. > > Let's say we have a system with: > 0 .. 0x1.0000.0000 > 0x100.0000.0000 .. 0x101.0000.0000 > > 2x4G, each is 1TB aligned. And we can map directly only the first 4GB > (because of the maximum IOMMU table size) but not the other. And 1:1 on > that "pseries" is done with offset=0x0800.0000.0000.0000. > > So we want to check every bus address against dev->bus_dma_limit, not > dev->coherent_dma_mask. In the example above I'd set bus_dma_limit to > 0x0800.0001.0000.0000 and 1:1 mapping for the second 4GB would not be > tried. Does this sound reasonable? Thanks, bus_dma_limit is just another limiting factor applied on top of coherent_dma_mask or dma_mask respectively. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu