On Fri, Apr 20, 2018 at 09:08:51AM -0700, Alexander Duyck wrote: > On Fri, Apr 20, 2018 at 8:28 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Fri, Apr 20, 2018 at 07:56:14AM -0700, Alexander Duyck wrote: > >> > I think for virtio it should include the feature bit, yes. > >> > Adding feature bit is very easy - post a patch to the virtio TC mailing > >> > list, wait about a week to give people time to respond (two weeks if it > >> > is around holidays and such). > >> > >> The problem is we are talking about hardware/FPGA, not software. > >> Adding a feature bit means going back and updating RTL. The software > >> side of things is easy, re-validating things after a hardware/FPGA > >> change not so much. > >> > >> If this is a hard requirement I may just drop the virtio patch, push > >> what I have, and leave it to Mark/Dan to deal with the necessary RTL > >> and code changes needed to support Virtio as I don't expect the > >> turnaround to be as easy as just a patch. > >> > >> Thanks. > >> > >> - Alex > > > > Let's focus on virtio in this thread. > > That is kind of what I was thinking, and why I was thinking it might > make sense to make the virtio specific changes a separate patch set. I > could get the PCI bits taken care of in the meantime since they effect > genetic PCI, NVMe, and the Amazon ENA interfaces. > > > Involving the virtio TC in host/guest interface changes is a > > hard requirement. It's just too easy to create conflicts otherwise. > > > > So you guys should have just sent the proposal to the TC when you > > were doing your RTL and you would have been in the clear. > > Agreed. I believe I brought this up when I was originally asked to > look into the coding for this. > > > Generally adding a feature bit with any extension is a good idea: > > this way you merely reserve a feature bit for your feature through > > the TC and are more or less sure of forward and backward compatibility. > > It's incredibly easy. > > Agreed, though in this case I am not sure it makes sense since this > isn't necessarily something that is a Virtio feature itself. It is > just a side effect of the fact that they are adding SR-IOV support to > a device that happens to emulate Virtio NET and apparently their PF > has to be identical to the VF other than the PCIe extended config > space. I got that. My point is not everyone implementing SR-IOV will want to do it like this. Others might want to have VFs be different from PFs somehow. Feature bits ensure forward not just backward compatibility. > > But maybe it's not needed here. I am not making the decisions myself. > > Not too late: post to the TC list and let's see what the response is. > > Without a feature bit you are making a change affecting all future > > implementations without exception so the bar is a bit higher: you need > > to actually post a spec text proposal not just a patch showing how to > > use the feature, and TC needs to vote on it. Voting takes a week, > > review a week or two depending on change complexity. > > > > Hope this helps, > > > > -- > > MST > > I think I will leave this for Dan and Mark to handle since I am still > not all that familiar with the hardware in use here. Once a decision > has been made him and Mark could look at pushing either the one line > patch or something more complex involving a feature flag. > > Thanks. > > Alex As long as the TC is involved. I know it's a bit of a strange thing to block it at the driver level, the issue is with the device, but it's literally the only handle I have to prevent people from doing out of spec hacks then pushing it all on us to maintain. -- MST
