Re: [Qemu-devel] Using PCI config space to indicate config location

[Michael S. Tsirkin]

On Fri, Oct 12, 2012 at 08:59:36AM +1030, Rusty Russell wrote:
> >> For writes, the standard seems to be a commit latch.  We could abuse the
> >> generation count for this: the driver writes to it to commit config
> >> changes.
> >
> > I think this will work. There are a couple of things that bother me:
> >
> > This assumes read accesses have no side effects, and these are sometimes 
> > handy.
> > Also the semantics for write aren't very clear to me.
> > I guess device must buffer data until generation count write?
> > This assumes the device has a buffer to store writes,
> > and it must track each byte written. I kind of dislike this
> > tracking of accessed bytes. Also, device would need to resolve conflicts
> > if any in some device specific way.
> 
> It should be trivial to implement: you keep a scratch copy of the config
> space, and copy it to the master copy when they hit the latch.
> 
> Implementation of this will show whether I've missed anything here, I
> think.

What I refer to: what happens if driver does:
- write offset 1
- write offset 3
- hit commit latch

?

-- 
MST