On Sat, Feb 15, 2020 at 03:10:47PM -0600, Bjorn Helgaas wrote: > On Thu, Feb 13, 2020 at 05:50:40PM +0100, Jean-Philippe Brucker wrote: > > Each vendor has their own way of describing whether a host bridge > > supports ATS. The Intel and AMD ACPI tables selectively enable or > > disable ATS per device or sub-tree, while Arm has a single bit for each > > host bridge. For those that need it, add an ats_supported bit to the > > host bridge structure. > > > > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> > > --- > > drivers/pci/probe.c | 7 +++++++ > > include/linux/pci.h | 1 + > > 2 files changed, 8 insertions(+) > > > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > > index 512cb4312ddd..75c0a25af44e 100644 > > --- a/drivers/pci/probe.c > > +++ b/drivers/pci/probe.c > > @@ -598,6 +598,13 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge) > > bridge->native_shpc_hotplug = 1; > > bridge->native_pme = 1; > > bridge->native_ltr = 1; > > + > > + /* > > + * Some systems may disable ATS at the host bridge (ACPI IORT, > > + * device-tree), other filter it with a smaller granularity (ACPI DMAR > > + * and IVRS). > > + */ > > + bridge->ats_supported = 1; > > The cover letter says it's important to enable ATS only if the host > bridge supports it. From the other patches, it looks like we learn if > the host bridge supports ATS from either a DT "ats-supported" property > or an ACPI IORT table. If that's the case, shouldn't the default here > be "ATS is *not* supported"? The ACPI IVRS table (AMD) doesn't have a property for the host bridge, it can only deselect ATS for a sub-range of devices. Similarly the DMAR table (Intel) declares that ATS is supported either by the whole PCIe domain or for sub-ranges of devices. I selected ats_supported at the bridge by default since IVRS needs it and DMAR has its own fine-grained ATS support configuration. I'm still not sure this is the right approach, given that the ats_supported bridge property doesn't exactly correspond to a firmware property on all platforms. Maybe the device-tree implementation should follow the IORT one where each device carries a fwspec property stating "root-complex supports ATS". But it isn't nice either so I tried a cleaner implementation (as discussed with Robin back on the ATS-with-SMMUv3 series [1]). Thanks, Jean [1] https://lore.kernel.org/linux-iommu/c10c7adb-c7f6-f8c6-05cc-f4f143427a2d@xxxxxxx/
