RE: [patch V2 25/33] PCI/MSI: Provide post-enable dynamic allocation interfaces for MSI-X

[Thomas Gleixner]

On Thu, Nov 24 2022 at 02:58, Kevin Tian wrote:
>> +
>> +/**
>> + * pci_msix_free_irq - Free an interrupt on a PCI/MSIX interrupt domain
>> + *		      which was allocated via pci_msix_alloc_irq_at()
>> + *
>> + * @dev:	The PCI device to operate on
>> + * @map:	A struct msi_map describing the interrupt to free
>> + *		as returned from the allocation function.
>> + */
>
> Can this be used on preallocated descriptors? If not any guard required
> or just treat it as a driver responsibility to not misuse?

The preallocated descriptors are only relevant during setup, but not
post setup. So yes, you can do:

pci_alloc_irq_vectors(dev, 10, 10, PCI_IRQ_MSIX);

and then

    map = { .index = 9, .virq = $IRQ };
    pci_msix_free_irq(dev, &map);

It just works.

>> +void pci_msix_free_irq(struct pci_dev *dev, struct msi_map map)
>> +{
>> +	if (WARN_ON_ONCE(map.index < 0 || map.virq <= 0))
>
> map.virq cannot be negative.

Why? Callers can make up whatever they want, no?

Thanks,

        tglx