On 19.03.2025 16:21, Mykyta Poturai wrote: > 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. > > 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.
An abridged version of this ought to go in the patch description, I think. This is special, so it needs calling out. As to the placement - would making an entirely new .c file possibly help? (Then, instead of in the patch description, maybe the special aspect could be put in a code comment at the top of the file.) Jan
