Re: [PATCH 0/2] Introduce PCI_FIXUP_IOMMU

[Bjorn Helgaas]

On Wed, Dec 16, 2020 at 07:24:30PM +0800, Zhou Wang wrote:
> On 2020/6/23 23:04, Bjorn Helgaas wrote:
> > On Fri, Jun 19, 2020 at 10:26:54AM +0800, Zhangfei Gao wrote:
> >> Have studied _DSM method, two issues we met comparing using quirk.
> >>
> >> 1. Need change definition of either pci_host_bridge or pci_dev, like adding
> >> member can_stall,
> >> while pci system does not know stall now.
> >>
> >> a, pci devices do not have uuid: uuid need be described in dsdt, while pci
> >> devices are not defined in dsdt.
> >>     so we have to use host bridge.
> > 
> > PCI devices *can* be described in the DSDT.  IIUC these particular
> > devices are hardwired (not plug-in cards), so platform firmware can
> > know about them and could describe them in the DSDT.
> > 
> >> b,  Parsing dsdt is in in pci subsystem.
> >> Like drivers/acpi/pci_root.c:
> >>        obj = acpi_evaluate_dsm(ACPI_HANDLE(bus->bridge), &pci_acpi_dsm_guid,
> >> 1,
> >>                                 IGNORE_PCI_BOOT_CONFIG_DSM, NULL);
> >>
> >> After parsing DSM in pci, we need record this info.
> >> Currently, can_stall info is recorded in iommu_fwspec,
> >> which is allocated in iommu_fwspec_init and called by iort_iommu_configure
> >> for uefi.
> > 
> > You can look for a _DSM wherever it is convenient for you.  It could
> > be in an AMBA shim layer.
> > 
> >> 2. Guest kernel also need support sva.
> >> Using quirk, the guest can boot with sva enabled, since quirk is
> >> self-contained by kernel.
> >> If using  _DSM, a specific uefi or dtb has to be provided,
> >> currently we can useQEMU_EFI.fd from apt install qemu-efi
> > 
> > I don't quite understand what this means, but as I mentioned before, a
> > quirk for a *limited* number of devices is OK, as long as there is a
> > plan that removes the need for a quirk for future devices.
> > 
> > E.g., if the next platform version ships with a DTB or firmware with a
> > _DSM or other mechanism that enables the kernel to discover this
> > information without a kernel change, it's fine to use a quirk to cover
> > the early platform.
> > 
> > The principles are:
> > 
> >   - I don't want to have to update a quirk for every new Device ID
> >     that needs this.
> 
> Hi Bjorn and Zhangfei,
> 
> We plan to use ATS/PRI to support SVA in future PCI devices. However, for
> current devices, we need to add limited number of quirk to let them
> work. The device IDs of current quirk needed devices are ZIP engine(0xa250, 0xa251),
> SEC engine(0xa255, 0xa256), HPRE engine(0xa258, 0xa259), revision id are
> 0x21 and 0x30.
> 
> Let's continue to upstream these quirks!

Please post the patches you propose.  I don't think the previous ones
are in my queue.  Please include the lore URL for the previous
posting(s) in the cover letter so we can connect the discussion.

> >   - I don't really want to have to manage non-PCI information in the
> >     struct pci_dev.  If this is AMBA- or IOMMU-related, it should be
> >     stored in a structure related to AMBA or the IOMMU.
> > .
> >