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    SubjectRe: [patch 34/39] PCI/MSI: Reject multi-MSI early
    On Fri, Nov 11, 2022 at 02:55:09PM +0100, Thomas Gleixner wrote:
    > When hierarchical MSI interrupt domains are enabled then there is no point
    > to do tons of work and detect the missing support for multi-MSI late in the
    > allocation path.
    >
    > Just query the domain feature flags right away. The query function is going
    > to be used for other purposes later and has a mode argument which influences
    > the result:
    >
    > ALLOW_LEGACY returns true when:
    > - there is no irq domain attached (legacy support)
    > - there is a irq domain attached which has the feature flag set
    >
    > DENY_LEGACY returns only true when:
    > - there is a irq domain attached which has the feature flag set
    >
    > This allows to use the function universally without ifdeffery in the
    > calling code.
    >
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

    Acked-by: Bjorn Helgaas <bhelgaas@google.com>

    > ---
    > drivers/pci/msi/irqdomain.c | 22 ++++++++++++++++++++++
    > drivers/pci/msi/msi.c | 4 ++++
    > drivers/pci/msi/msi.h | 9 +++++++++
    > 3 files changed, 35 insertions(+)
    >
    > --- a/drivers/pci/msi/irqdomain.c
    > +++ b/drivers/pci/msi/irqdomain.c
    > @@ -187,6 +187,28 @@ struct irq_domain *pci_msi_create_irq_do
    > }
    > EXPORT_SYMBOL_GPL(pci_msi_create_irq_domain);
    >
    > +/**
    > + * pci_msi_domain_supports - Check for support of a particular feature flag
    > + * @pdev: The PCI device to operate on
    > + * @feature_mask: The feature mask to check for (full match)
    > + * @mode: If ALLOW_LEGACY this grants the feature when there is no irq domain
    > + * associated to the device. If DENY_LEGACY the lack of an irq domain
    > + * makes the feature unsupported

    Looks like some of these might be wider than 80 columns, which I think
    was the typical width of this file.

    > + */
    > +bool pci_msi_domain_supports(struct pci_dev *pdev, unsigned int feature_mask,
    > + enum support_mode mode)
    > +{
    > + struct msi_domain_info *info;
    > + struct irq_domain *domain;
    > +
    > + domain = dev_get_msi_domain(&pdev->dev);
    > +
    > + if (!domain || !irq_domain_is_hierarchy(domain))
    > + return mode == ALLOW_LEGACY;
    > + info = domain->host_data;
    > + return (info->flags & feature_mask) == feature_mask;
    > +}
    > +
    > /*
    > * Users of the generic MSI infrastructure expect a device to have a single ID,
    > * so with DMA aliases we have to pick the least-worst compromise. Devices with
    > --- a/drivers/pci/msi/msi.c
    > +++ b/drivers/pci/msi/msi.c
    > @@ -347,6 +347,10 @@ static int msi_capability_init(struct pc
    > struct msi_desc *entry;
    > int ret;
    >
    > + /* Reject multi-MSI early on irq domain enabled architectures */
    > + if (nvec > 1 && !pci_msi_domain_supports(dev, MSI_FLAG_MULTI_PCI_MSI, ALLOW_LEGACY))
    > + return 1;
    > +
    > /*
    > * Disable MSI during setup in the hardware, but mark it enabled
    > * so that setup code can evaluate it.
    > --- a/drivers/pci/msi/msi.h
    > +++ b/drivers/pci/msi/msi.h
    > @@ -97,6 +97,15 @@ int __pci_enable_msix_range(struct pci_d
    > void __pci_restore_msi_state(struct pci_dev *dev);
    > void __pci_restore_msix_state(struct pci_dev *dev);
    >
    > +/* irq_domain related functionality */
    > +
    > +enum support_mode {
    > + ALLOW_LEGACY,
    > + DENY_LEGACY,
    > +};
    > +
    > +bool pci_msi_domain_supports(struct pci_dev *dev, unsigned int feature_mask, enum support_mode mode);
    > +
    > /* Legacy (!IRQDOMAIN) fallbacks */
    >
    > #ifdef CONFIG_PCI_MSI_ARCH_FALLBACKS
    >

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