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    Subject[patch 34/39] PCI/MSI: Reject multi-MSI early
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    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>
    ---
    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
    + */
    +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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