On Sat, Nov 27, 2021 at 02:18:34AM +0100, Thomas Gleixner wrote:

The [PCI] MSI code has gained quite some warts over time. A recent
discussion unearthed a shortcoming: the lack of support for expanding
PCI/MSI-X vectors after initialization of MSI-X.

PCI/MSI-X has no requirement to setup all vectors when MSI-X is enabled in
the device. The non-used vectors have just to be masked in the vector
table. For PCI/MSI this is not possible because the number of vectors
cannot be changed after initialization.

The PCI/MSI code, but also the core MSI irq domain code are built around
the assumption that all required vectors are installed at initialization
time and freed when the device is shut down by the driver.

Supporting dynamic expansion at least for MSI-X is important for VFIO so
that the host side interrupts for passthrough devices can be installed on
demand.

This is the first part of a large (total 101 patches) series which
refactors the [PCI]MSI infrastructure to make runtime expansion of MSI-X
vectors possible. The last part (10 patches) provide this functionality.

The first part is mostly a cleanup which consolidates code, moves the PCI
MSI code into a separate directory and splits it up into several parts.

No functional change intended except for patch 2/N which changes the
behaviour of pci_get_vector()/affinity() to get rid of the assumption that
the provided index is the "index" into the descriptor list instead of using
it as the actual MSI[X] index as seen by the hardware. This would break
users of sparse allocated MSI-X entries, but non of them use these
functions.

I don't know all the irqdomain stuff all that well anymore, but I read
through all the patches and only noticed a small spello

[patch 02/22] PCI/MSI: Fix pci_irq_vector()/pci_irq_get_attinity()
                                                         ^^^^ ff

It all seems good, I especially like the splitting of msi.c and
removal of ops..

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Thanks,
Jason