On Fri, 30 Nov 2018 at 07:40, Markus Armbruster <arm...@redhat.com> wrote: > Peter Maydell <peter.mayd...@linaro.org> writes: > > Add an assert somewhere and catch it with the usual > > "instantiate everything" qtest?
> The troublemaker is (3), where we may end up with an overridden > realize-like method and an non-matching, un-overridden unrealize-like > method. Got any smart ideas? Mmm, I see the difficulty. I suppose in theory we could have a custom linter like clang-tidy and check that anything that sets a realize pointer also sets an unrealize, but that's pie-in-the-sky territory at the moment. Asserting that there is an unrealize would catch at least some cases of "forgot to handle hotplug", though, right? > > More generally, what is causing dc390 to be hotpluggable? > > I can't see anything obvious in the class init. > > It's a PCI device. These are all hot-pluggable by default. Maybe we should change that? Most people writing a PCI device are probably not thinking about hotplug. Though in the dc390 case it would probably not help to have to set a dc->hotpluggable flag, because it would inherit that from am53c974 too. I wonder if the dc390 could be structured in a way that it doesn't subclass a complete non-abstract pci device like that... > > If we > > have APIs where the default is "you get this weird thing > > you weren't thinking about but it's broken because > > you weren't thinking about it" then we will have a whole > > class of bugs that we then need to squash device by device[*]. > > I think it would be better for devices to have to explicitly > > opt in to implementing things like hotplug -- that way the > > failure mode is just "this isn't hotpluggable", we can > > report that helpfully to the user, and if anybody cares > > they can add the support. > > I tend to agree, although for PCI devices, not being hot-pluggable is > kind of weird, except for the ones that only occur soldered onto > mainboards. Real hardware PCI devices are not hot-pluggable by default as far as I'm aware; PCIe may be hot-pluggable but I think need to be designed to support it. This is a random non-hotplug-safe PCIe card: https://i.stack.imgur.com/tXug5.jpg PRSNT2# (pin 17 side B) is connected to Ground on pin 18 (these are the rightmost two connections visible); for hotplug it must be connected to PRSNT1# (which is pin 1 side A), AIUI. But the hardware situation is kind of a tangent from how we try to design our APIs. thanks -- PMM
