On Wed, 2011-11-09 at 23:14 +0200, Michael S. Tsirkin wrote: > On Wed, Nov 09, 2011 at 10:57:28PM +0200, Sasha Levin wrote: > > On Wed, 2011-11-09 at 22:52 +0200, Michael S. Tsirkin wrote: > > > On Wed, Nov 09, 2011 at 10:24:47PM +0200, Sasha Levin wrote: > > > > On Wed, 2011-11-09 at 21:59 +0200, Michael S. Tsirkin wrote: > > > > > > > > [snip] > > > > > > > > > +\begin_layout Enumerate > > > > > +Reset the device. > > > > > + This is not required on initial start up. > > > > > +\end_layout > > > > > + > > > > > +\begin_layout Enumerate > > > > > +The ACKNOWLEDGE status bit is set: we have noticed the device. > > > > > +\end_layout > > > > > + > > > > > +\begin_layout Enumerate > > > > > +The DRIVER status bit is set: we know how to drive the device. > > > > > +\end_layout > > > > > + > > > > > +\begin_layout Enumerate > > > > > + > > > > > +\change_inserted 1986246365 1320838089 > > > > > +PCI capability list scan, detecting virtio configuration layout using Virtio > > > > > + Structure PCI capabilities. > > > > > > > > Does the legacy space always gets mapped from BAR0? > > > > > > > > If yes, > > > > > > Yes and this is repeated in several places. Not clear? How can this > > > be made clearer? > > > > Do you mean comments such as "For backwards compatibility, devices > > should also present legacy configuration space in the first I/O region > > of the PCI device"? What I understood from it is that the device should > > have a legacy config in case it's used with an older guest, but I didn't > > understand from it that the legacy config will be used even if new > > layout is present. > > Yes, this is what I meant. New guest is required to use the new space > and not the legacy one. So you dont need a legacy space for the at all. > But practically, we'll need to support old guests for a long while. > > > > > It'll be a bit harder deprecating it in the future. > > > > > > Harder than ... what ? > > > > Harder than allowing devices not to present it at all if new layout > > config is used. > > Yes, it's allowed if you know you have a new guest. It says > explicitly that drivers are required to use new capabilities > is they are there. > > > Right now the simple implementation is to use MMIO for > > config and device specific, and let it fallback to legacy for ISR and > > notifications (and therefore, this is probably how everybody will > > implement it), which means that when you do want to deprecate legacy, > > there will be extra work to be done then, instead of doing it now. > > If hypervisors don't implement the new layout then drivers will > have to keep supporting the old one. I don't think we can do > much about that. > > > > IMO there's no way to put legacy anywhere except the first BAR > > > without breaking existing guests. > > > > It's not about where we put legacy, it's about how easy it is to drop > > legacy entirely. > > We can only do this after all guests and hypervisors are updated. When > they are, we can drop legacy from drivers and hypervisors, and > I don't see a way to make it easier. Well, in that case, why does the PCI cap probing is #4 in the device init list? Shouldn't we getting the layout and mapping it before we write to the status byte? -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
