Re: [virtio] Re: [virtio-dev] [PATCH] content: add vendor specific cfg type

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

On Wed, Nov 27, 2019 at 08:59:56AM +0100, Cornelia Huck wrote:
> On Mon, 25 Nov 2019 03:11:43 -0500
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Mon, Nov 25, 2019 at 08:45:52AM +0100, Jan Kiszka wrote:
> > > On 28.10.19 11:55, Michael S. Tsirkin wrote:  
> > > > Vendors might want to add their own capability
> > > > in the PCI capability list. However, Virtio already
> > > > uses the vendor specific capability ID (0x09)
> > > > for its own purposes.  
> > > 
> > > Did some vendor express that need, or do we only assume it so far? IOW: Do
> > > we know at least once concrete use case?  
> > 
> > Good point, I should have added this in the log.
> > 
> > I know of a device that implements virtio and has a bug.
> > 
> > Device is a transitional one so can not have vendor specific
> > subsystem IDs (that violates the SHOULD below. Do we want to qualify
> > that this recommendation is for non-transitional devices?). While that
> 
> What about adding some notes on top that vendor specific subsystem IDs
> are not for transitional devices? That would also catch the case in the
> other update.

I'm still trying to figure out a good wording though.
A full description would need to describe the legacy
tricks with subsystem device ID etc. That's a lot of
text. Certainly doable but
maybe I'll just drop the subsystem vendor ID part
for now, treat that as a different subject?

> > specific device can't be fixed like this on bare metal, it creates a consistent way
> > for future devices to trigger vendor/device specific quirks,
> > and it creates an option for the hypervisor to add the capability.
> > 
> > > > 
> > > > Provide a structure for vendor specific extensions.
> > > > 
> > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > > ---
> > > >   content.tex | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > >   1 file changed, 80 insertions(+)
> 
> > > > +\devicenormative{\subsection}{Vendor data capability}{Virtio
> > > > +Transport Options / Virtio Over PCI Bus / PCI Device Layout /
> > > > +Vendor data capability}
> > > > +
> > > > +The device SHOULD present the PCI subsystem vendor ID matching
> > > > +the device vendor, at offset 0x2C in its PCI configuration space
> > > > +header.
> > > > +
> > > > +Devices CAN present \field{vendor_id} that does not match
> > > > +either the PCI Vendor ID or the PCI Subsystem Vendor ID.
> > > > +
> > > > +Devices CAN present multiple Vendor data capabilities with
> > > > +either different or identical \field{vendor_id} values.
> > > > +
> > > > +The value \field{vendor_id} MUST NOT equal 0x1AF4.
> > > > +
> > > > +The size of the Vendor data capability MUST be a multiple of 4 bytes.
> > > > +
> > > > +Reads of the Vendor data capability by the driver MUST NOT have any
> > > > +side effects.