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Subject: Re: [virtio] Groups - Action Item "Create text version of virtio 0.9.5 document" added

On Wed, Jul 31, 2013 at 10:58:21AM +0100, Pawel Moll wrote:
> On Wed, 2013-07-31 at 10:46 +0100, Michael S. Tsirkin wrote:
> > > 	o NOP/null/dummy device
> > > 
> > > Reserve ID 0 for devices with no function and specify drivers behaviour
> > > for them. Usecase: qemu folk want to be able to create a pool of memory
> > > mapped devices and assign functions to them later, although before the
> > > OS is actually initialized.
> >
> > Sounds a bit crazy, 
> Thank you :-)
> > probably won't work for PCI (spec violation).
> Em, which one of specs? What I'm talking about is reserving a "Subsystem
> Device ID" (p.2.1 of the current spec) value 0 to a "device that does
> nothing" (is not a network card, nor block device, nor console, nor etc.
> nor anything else) and specifying how is the guest supposed to behave
> with such device (do nothing). In the current speech it would be
> "Appendix I: Doing Nothing Device", following "Appendix I: SCSI Host
> Device". How does this break anything?

It doesn't but then it will have to keep doing nothing :)
The current spec actually doesn't work either - I was going
to open an item for this - is the system open already?

Basically OS-es expect each PCI device to declare the function using device ID,
not subsystem device ID.
Linux is more flexible bug e.g. windows isn't, so windows
drivers require device id to match the intended function.

> > Link to a discussion?
> http://thread.gmane.org/gmane.linux.kernel.virtualization/20144
> Paweł
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