On 17.03.25 16:56, Jan Beulich wrote: > On 14.03.2025 14:34, Mykyta Poturai wrote: >> From: Oleksandr Tyshchenko <oleksandr_tyshche...@epam.com> >> >> The main purpose of this patch is to add a way to register PCI device >> (which is behind the IOMMU) using the generic PCI-IOMMU DT bindings [1] >> before assigning that device to a domain. >> >> This behaves similarly to the existing iommu_add_dt_device API, except it >> handles PCI devices, and it is to be invoked from the add_device hook in the >> SMMU driver. >> >> The function dt_map_id to translate an ID through a downstream mapping >> (which is also suitable for mapping Requester ID) was borrowed from Linux >> (v5.10-rc6) and updated according to the Xen code base. >> >> [1] >> https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/pci-iommu.txt >> >> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshche...@epam.com> >> Signed-off-by: Stewart Hildebrand <stewart.hildebr...@amd.com> >> Signed-off-by: Mykyta Poturai <mykyta_potu...@epam.com> >> --- >> Regarding pci_for_each_dma_alias question: getting host bridge node >> directly seems like a simpler solution with the same result. AFAIU >> with pci_for_each_dma_alias in linux we would arrive to the host brige >> node anyway, but also try to call dt_map_id for each device along the >> way. I am not sure why exactly it is done this way in linux, as >> according to the pci-iommu.txt, iommu-map node can only be present in >> the PCI root. >> >> v8->v9: >> * replace DT_NO_IOMMU with 1 >> * guard iommu_add_pci_sideband_ids with CONFIG_ARM > > I fear I'm confused: Isn't this contradicting ... > >> v7->v8: >> * ENOSYS->EOPNOTSUPP >> * move iommu_add_pci_sideband_ids to iommu.c to fix x86 build > > ... this earlier change? Really, with there being no caller, I can't see > why there could be any build issue here affecting only x86. Except for > Misra complaining about unreachable code being introduced, which I'm sure > I said before should be avoided.
The original reason for moving this function was the conflicting ACPI and EFI headers, I described it in V8 comments here[1]. > >> --- a/xen/drivers/passthrough/iommu.c >> +++ b/xen/drivers/passthrough/iommu.c >> @@ -20,6 +20,7 @@ >> #include <xen/param.h> >> #include <xen/softirq.h> >> #include <xen/keyhandler.h> >> +#include <xen/acpi.h> >> #include <xsm/xsm.h> >> >> #ifdef CONFIG_X86 >> @@ -744,6 +745,20 @@ int __init >> iommu_get_extra_reserved_device_memory(iommu_grdm_t *func, >> return 0; >> } >> >> +#ifdef CONFIG_ARM > > I realize we have CONFIG_X86 here as well (visible even in context of the > earlier hunk. Yet then the goal ought to be to reduce these anomalies, not > add new ones. Since I don't have a clear picture of what's wanted, I'm also > in trouble suggesting any alternative, I'm afraid. > > Jan Here is a short summary: The main problem is that we need this function somewhere, but there is no good place for it. It is only called on ARM for now but it's not ARM-specific by nature and can be eventually used on other platforms as well. It can't be just dropped because of the effort to support the co-existence of DT and ACPI. It also can't be declared as a static function because it requires the inclusion of <xen/acpi.h> for acpi_disabled define, which leads to build errors[1]. And without ifdef guards it would be a MISRA violation. [1] https://patchew.org/Xen/cover.1739182214.git.mykyta._5fpotu...@epam.com/67b9bd138c12c0df35e5c4b3137c30ad345097d5.1739182214.git.mykyta._5fpotu...@epam.com/#e6ea52a3-c7ce-411f-8186-cf725aa60...@epam.com -- Mykyta
