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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] xen/arm: do not try to add pci-domain for disabled devices
On 28.10.21 19:50, Stefano Stabellini wrote: > On Thu, 28 Oct 2021, Julien Grall wrote: >> Hi Stefano, >> >> On 28/10/2021 00:57, Stefano Stabellini wrote: >>> On Wed, 27 Oct 2021, Julien Grall wrote: >>>> Hi Oleksandr, >>>> >>>> On 27/10/2021 09:37, Oleksandr Andrushchenko wrote: >>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx> >>>>> >>>>> If a PCI host bridge device is present in the device tree, but is >>>>> disabled, then its PCI host bridge driver was not instantiated. >>>>> This results in the following panic during Xen start: >>>>> >>>>> (XEN) Device tree generation failed (-22). >>>> It would good to clarify in the commit message where the error is coming >>>> from. >>>> I think this is from pci_get_host_bridge_segment(). >>>> >>>>> (XEN) >>>>> (XEN) **************************************** >>>>> (XEN) Panic on CPU 0: >>>>> (XEN) Could not set up DOM0 guest OS >>>>> (XEN) **************************************** >>>>> >>>>> Fix this by not adding linux,pci-domain property for hwdom if it is >>>>> neither available nor device enabled. >>>> From my reading of the binding [1], the property should be present in all >>>> the >>>> hostbridges if one specify it. IOW, I think the property should also be >>>> added >>>> for hostbridges that are not available. >>> Just wanted to say that I think you are right: >>> >>> """ >>> It is required to either not set this property at all or set it for all >>> host bridges in the system, otherwise potentially conflicting domain numbers >>> may be assigned to root buses behind different host bridges. The domain >>> number for each host bridge in the system must be unique. >>> """ >>> >>> and I am ready to believe device trees with disabled bridges might have >>> (incorrectly) ignored the rule. >> Looking at linux/arch/arm64/boot/dts/, there are a few Device-Tree that >> contain the property "linux,pci-domain". All of them seems to also add it for >> disabled hostbridges. >> >> However, I am under the impression that it is more common to have a >> Devide-Tree without any property "linux,pci-domain". When PCI support is >> enabled, Xen will generate the domain ID for the hostbridge and write it to >> the DT. >> >> This doesn't work for disabled hostbridge and I think this is Oleksandr's >> problem. @Oleksandr can you confirm it? >> >>> >>>> AFAICT, Linux will ignore hostbridge that are not available. But it feels >>>> to >>>> me we are twisting the rule. So, could we consider to allocate an unused >>>> number? >>> I think that would be fine but it doesn't look easy from the current Xen >>> code point of view because the allocation depends on the Xen driver, >>> which we don't have. But I'll let others comment on it. >> So what matters is Xen doesn't make things worse. We have two cases to care: >> 1) Xen only has drivers for a part of the hostbriges >> 2) Some hostbriges are disabled >> >> Case 1) will definitely generate a DT that will make Linux unhappy if we have >> don't add the property consistently. > Good point! So, the bottom line: we add the property regardless of the status? And the segment we assign for the disabled ones is pci_get_new_domain_nr()? I guess nothing bad happens if we have say 3 bridges: okay - > seg 0 disabled - > seg 1 okay - > seg 2
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