"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes: > 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 - nothing - nothing - effect of offset 1 and offset 3 writes Now, since there's nothing published by the *driver* at the moment which can't be trivially atomically written, this scheme is overkill (sure, it means you could do a byte-at-a-time write to some 4-byte field, but why?). But perhaps it's overkill: no other bus has this feature, so we'd need a feature bit for them anyway in future if we create a device which needs such atomicity. Cheers, Rusty. -- 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
