> From: Chatre, Reinette <reinette.chatre@xxxxxxxxx> > Sent: Thursday, May 11, 2023 11:45 PM > > pci_msix_alloc_irq_at() enables an individual MSI-X interrupt to be > allocated after MSI-X enabling. > > Use dynamic MSI-X (if supported by the device) to allocate an interrupt > after MSI-X is enabled. An MSI-X interrupt is dynamically allocated at > the time a valid eventfd is assigned. This is different behavior from > a range provided during MSI-X enabling where interrupts are allocated > for the entire range whether a valid eventfd is provided for each > interrupt or not. > > The PCI-MSIX API requires that some number of irqs are allocated for > an initial set of vectors when enabling MSI-X on the device. When > dynamic MSIX allocation is not supported, the vector table, and thus > the allocated irq set can only be resized by disabling and re-enabling > MSI-X with a different range. In that case the irq allocation is > essentially a cache for configuring vectors within the previously > allocated vector range. When dynamic MSI-X allocation is supported, > the API still requires some initial set of irqs to be allocated, but > also supports allocating and freeing specific irq vectors both > within and beyond the initially allocated range. > > For consistency between modes, as well as to reduce latency and improve > reliability of allocations, and also simplicity, this implementation > only releases irqs via pci_free_irq_vectors() when either the interrupt > mode changes or the device is released. > > Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx> > Link: > https://lore.kernel.org/lkml/20230403211841.0e206b67.alex.williamson@re > dhat.com/ Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
