PCI Driver Requirements: ISR status capability

[Ladi Prosek <lprosek@redhat.com>]

Hello virtio-comment,

This is a comment on the wording of "4.1.4.5.2 Driver Requirements:
ISR status capability" in virtio 1.0 spec CS 04, copied below.

Reading ISR status if MSI is enabled is not guaranteed to give any
meaningful results and the behavior should be specified as "undefined"
and/or the requirement level should be "MUST NOT". The use of "SHOULD
NOT" indicates optionality and the sentence may be interpreted as a
perf optimization suggestion (no need to read ISR status because the
MSI interrupt provides the required information), giving the
impression that there are circumstances when accessing the capability
is in fact useful.

4.1.4.5.2 Driver Requirements: ISR status capability

If MSI-X capability is enabled, the driver SHOULD NOT access ISR
status upon detecting a Queue Interrupt.

Thanks!
Ladi