On 19.03.25 17:28, Jan Beulich wrote: > 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
It seems to me creating a new file would be overkill for one small function. I considered moving it to xen/drivers/passthrough/arm/iommu.c to reduce ifdefs but I feared it would suggest that it is arch-specific a bit too strongly. So maybe move it there after all if you think it would be better? -- Mykyta
