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Subject: Re: [virtio-dev] [PATCH 08/11] transport-pci: Introduce virtio extended capability
On Mon, Apr 10, 2023 at 2:24âPM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Mon, Apr 10, 2023 at 09:36:17AM +0800, Jason Wang wrote: > > On Fri, Mar 31, 2023 at 7:00âAM Parav Pandit <parav@nvidia.com> wrote: > > > > > > PCI device configuration space for capabilities is limited to only 192 > > > bytes shared by many PCI capabilities of generic PCI device and virtio > > > specific. > > > > > > Hence, introduce virtio extended capability that uses PCI Express > > > extended capability. > > > Subsequent patch uses this virtio extended capability. > > > > > > Co-developed-by: Satananda Burla <sburla@marvell.com> > > > Signed-off-by: Parav Pandit <parav@nvidia.com> > > > > Can you explain the differences compared to what I've used to propose? > > > > https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg08078.html > > > > This can save time for everybody. > > > > Thanks > > BTW another advantage of extended capabilities is - these are actually > cheaper to access from a VM than classic config space. Config space/BAR is allowed by both of the proposals or anything I missed? > > > Several points > - I don't like it that yours is 32 bit. We do not need 2 variants just > make it all 64 bit That's fine. > - We need to document that if driver does not scan extended capbilities it will not find them. This is implicit since I remember we don't have such documentation for pci capability, anything makes pcie special? > And existing drivers do not scan them. So what is safe > to put there? vendor specific? extra access types? For PASID at least, since it's a PCI-E feature, vendor specific should be fine. Not sure about legacy MMIO then. > Can we make scanning these mandatory in future drivers? future devices? > I guess we can add a feature bit to flag that. For PASID, it doesn't need this, otherwise we may duplicate transport specific features. > Is accessing these possible from bios? Not at least for the two use cases now PASID or legacy MMIO. > > So I like this one better as a basis - care reviewing it and adding > stuff? There are very few differences and I will have a look. Thanks > > -- > MST >
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