Re: [virtio-comment] comment on pci section

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jan 29, 2014 at 04:38:58PM +1030, Rusty Russell wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
> > Two comments received from a co-worker:
> >
> > 3.1 "The device MUST NOT consume buffers before DRIVER_OK ..." - I
> > personally
> > would like to see also something like:  "device must not generate
> > interrupts if
> > DRIVER_OK is not set” to better handle power management transitions.
> 
> That addition seems to make sense, but I don't understand the reference
> to power management transitions?

Well - ATM we do things like suspend by device reset and re-initialization,
right? I'm guessing during e.g. resume it's important not to get
interrupts too early. I'll check.

Hmm actually we have a chapter about initialization but not cleanup.
Might be a good addition.

Also, I note that QEMU implemented master abort bit by
clearing DRIVER_OK - AFAIK useful to stop device in a
standard way if driver malfunctions.

Also with QEMU you can clear DRIVER_OK and this stops the device. I
wonder if someone uses this.

> > 4.1.3.1.1.
> > Must clarify that all devices MUST support all cfg_type values 1-5.
> > This way BIOS can limit type 5 exclusively and drivers don't
> > need to add support for type 5.
> 
> The word "support" here is unclear to me.  Are you saying that a device
> MUST offer a VIRTIO_PCI_CAP_PCI_CFG value?  Something like:
> 
>         Drivers MUST offer at least one capability of each type.

Exactly. Except

> Thanks,
> Rusty.