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. - 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. _______________________________________________ iommu mailing list firstname.lastname@example.org https://lists.linuxfoundation.org/mailman/listinfo/iommu