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Subject: Re: PCI Driver Requirements: ISR status capability
On Fri, May 06, 2016 at 09:28:20AM +0200, Ladi Prosek wrote: > 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 I think I agree. I would add something like: If MSI-X capability is enabled, the driver MUST ignore bit 0 (Queue Interrupt) in the ISR register. -- MST
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