Re: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()

[Thomas Gleixner]

Logan,

On Mon, Nov 29 2021 at 11:21, Logan Gunthorpe wrote:
> On 2021-11-26 6:23 p.m., Thomas Gleixner wrote:
>> Replace the about to vanish iterators, make use of the filtering and take
>> the descriptor lock around the iteration.
>
> This patch looks good to me:
>
> Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>

thanks for having a look at this. While I have your attention, I have a
question related to NTB.

The switchtec driver is the only one which uses PCI_IRQ_VIRTUAL in order
to allocate non-hardware backed MSI-X descriptors.

AFAIU these descriptors are not MSI-X descriptors in the regular sense
of PCI/MSI-X. They are allocated via the PCI/MSI mechanism but their
usage is somewhere in NTB which has nothing to do with the way how the
real MSI-X interrupts of a device work which explains why we have those
pci.msi_attrib.is_virtual checks all over the place.

I assume that there are other variants feeding into NTB which can handle
that without this PCI_IRQ_VIRTUAL quirk, but TBH, I got completely lost
in that code.

Could you please shed some light on the larger picture of this?

Thanks,

        tglx