On Tue, Oct 9, 2018 at 9:03 AM Sunil Kovvuri <sunil.kovvuri@xxxxxxxxx> wrote:
> On Mon, Oct 8, 2018 at 5:38 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > On Sun, Oct 7, 2018 at 5:01 PM <sunil.kovvuri@xxxxxxxxx> wrote:
> >
> > >
> > > + /* HW interprets RVU_AF_MSIXTR_BASE address as an IOVA, hence
> > > + * create a IOMMU mapping for the physcial address configured by
> > > + * firmware and reconfig RVU_AF_MSIXTR_BASE with IOVA.
> > > + */
> > > + cfg = rvu_read64(rvu, BLKADDR_RVUM, RVU_PRIV_CONST);
> > > + max_msix = cfg & 0xFFFFF;
> > > + phy_addr = rvu_read64(rvu, BLKADDR_RVUM, RVU_AF_MSIXTR_BASE);
> > > + iova = dma_map_single(rvu->dev, (void *)phy_addr,
> > > + max_msix * PCI_MSIX_ENTRY_SIZE,
> > > + DMA_BIDIRECTIONAL);
> > > + if (dma_mapping_error(rvu->dev, iova))
> > > + return -ENOMEM;
> > > +
> > > + rvu_write64(rvu, BLKADDR_RVUM, RVU_AF_MSIXTR_BASE, (u64)iova);
> > > + rvu->msix_base_iova = iova;
> > > +
> >
> > I'm a bit puzzled by how this works. Does this rely on a specific iommu
> > driver implementation? Normally a physical address makes no sense to the
> > implementation backing dma_map_single() that tries to convert a
> > linear kernel virtual address into a physical address.
> >
> > Arnd
>
> I understand what you are pointing at, but we did test this.
> IOMMU on this silicon is standard ARM64 SMMUv3.
I didn't doubt that you get the right results, I just couldn't see how ;-)
> All dma_map_single does is virt_to_page and iommu_dma_map_page
> converts it back i.e page_to_phys.
> So the IOMMU driver gets the same physical address passed above and
> creates a iova translation mapping.
>
> For reference below is the captured debug info for the same
> =====
> [ 19.435968] rvu_setup_msix_resources: phy_addr 0x3200000 iova 0xfff80000
> [ 19.436967] rvu_setup_msix_resources: virt_to_page(phy_addr)
> 0xffff7fe00000c800 page_to_phys(page) 0x3200000
> offset_in_page(phy_addr) 0x00
> =====
I think if you enable CONFIG_DEBUG_VIRTUAL, the virt_to_page()
above should trigger a warning in
phys_addr_t __virt_to_phys(unsigned long x)
{
WARN(!__is_lm_address(x),
"virt_to_phys used for non-linear address: %pK (%pS)\n",
(void *)x,
(void *)x);
return __virt_to_phys_nodebug(x);
}
Can you verify that?
Arnd
