On Mon, 8 Jun 2020, Christoph Hellwig wrote: > On Wed, Jun 03, 2020 at 03:22:44PM -0700, Stefano Stabellini wrote: > > From: Stefano Stabellini <stefano.stabell...@xilinx.com> > > > > With some devices physical addresses are different than dma addresses. > > To be able to deal with these cases, we need to call phys_to_dma on > > physical addresses (including machine addresses in Xen terminology) > > before returning them from xen_swiotlb_alloc_coherent and > > xen_swiotlb_map_page. > > > > We also need to convert dma addresses back to physical addresses using > > dma_to_phys in xen_swiotlb_free_coherent and xen_swiotlb_unmap_page if > > we want to do any operations on them. > > > > Call dma_to_phys in is_xen_swiotlb_buffer. > > Call phys_to_dma in xen_phys_to_bus. > > Call dma_to_phys in xen_bus_to_phys. > > > > Everything is taken care of by these changes except for > > xen_swiotlb_alloc_coherent and xen_swiotlb_free_coherent, which need a > > few explicit phys_to_dma/dma_to_phys calls. > > > > Signed-off-by: Stefano Stabellini <stefano.stabell...@xilinx.com> > > Tested-by: Corey Minyard <cminy...@mvista.com> > > Tested-by: Roman Shaposhnik <ro...@zededa.com> > > --- > > Changes in v2: > > - improve commit message > > --- > > drivers/xen/swiotlb-xen.c | 22 ++++++++++++---------- > > 1 file changed, 12 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c > > index 0a6cb67f0fc4..60ef07440905 100644 > > --- a/drivers/xen/swiotlb-xen.c > > +++ b/drivers/xen/swiotlb-xen.c > > @@ -64,16 +64,16 @@ static inline dma_addr_t xen_phys_to_bus(struct device > > *dev, phys_addr_t paddr) > > > > dma |= paddr & ~XEN_PAGE_MASK; > > > > - return dma; > > + return phys_to_dma(dev, dma); > > So looking at this function: > > The dma name for something passed to phys_to_dma is really > weird.
Yeah, that is true, I am not sure why I chose that confusing name. I'll rename it. > The fact that the comments says don't use XEN_PFN_PHYS > beause of the type mismatch while nothing but swiotlb-xen is the only > user of XEN_PFN_PHYS is also weird. I think XEN_PFN_PHYS needs to move > to swiotlb-xen first, then use a hardcoded u64 for the size, and the > split the function into a phys_to_xen_phys (or so) function where > the result gets passed to phys_to_dma. I understand what you are suggesting about having something like: xen_phys_to_dma(...) { phys_addr_t phys = xen_phys_to_bus(dev, paddr) return phys_to_dma(phys); } I thought about it myself. I'll do it. But I don't think I understood the comment about XEN_PFN_PHYS. > Similar for the reverse direction. OK