Am 28.07.2022 um 16:50 hat Markus Armbruster geschrieben: > Kevin Wolf <kw...@redhat.com> writes: > > > Am 28.07.2022 um 11:46 hat Peter Maydell geschrieben: > >> On Wed, 27 Jul 2022 at 20:03, Kevin Wolf <kw...@redhat.com> wrote: > >> > > >> > Am 18.07.2022 um 11:49 hat Markus Armbruster geschrieben: > >> > > An OTP device isn't really a parallel flash, and neither are eFuses. > >> > > More fast-and-lose use of IF_PFLASH may exist in the tree, and maybe of > >> > > other interface types, too. > >> > > > >> > > This patch introduces IF_OTHER. The patch after next uses it for an > >> > > EEPROM device. > >> > > > >> > > Do we want IF_OTHER? > >> > > >> > What would the semantics even be? Any block device that doesn't pick up > >> > a different category may pick up IF_OTHER backends? > >> > > >> > It certainly feels like a strange interface to ask for "other" disk and > >> > then getting as surprise what this other thing might be. It's > >> > essentially the same as having an explicit '-device other', and I > >> > suppose most people would find that strange. > >> > > >> > > If no, I guess we get to abuse IF_PFLASH some more. > >> > > > >> > > If yes, I guess we should use IF_PFLASH only for actual parallel flash > >> > > memory going forward. Cleaning up existing abuse of IF_PFLASH may not > >> > > be worth the trouble, though. > >> > > > >> > > Thoughts? > >> > > >> > If the existing types aren't good enough (I don't have an opinion on > >> > whether IF_PFLASH is a good match), let's add a new one. But a specific > >> > new one, not just "other". > >> > >> I think the common thread is "this isn't what anybody actually thinks > >> of as being a 'disk', but we would like to back it with a block device > >> anyway". That can cover a fair range of possibilities... > > > > How confident are we that no board will ever have two devices of this > > kind? > > > > As long as every board has at most one, if=other is a bad user interface > > in terms of descriptiveness, but still more or less workable as long as > > you know what it means for the specific board you use. > > > > But if you have more than one device, it becomes hard to predict which > > device gets which backend - it depends on the initialisation order in > > the code then, > > Really? Board code should use IF_OTHER devices just like it uses the > other interface types, namely connecting each frontend device to a > backend device with a well-known and fixed interface type and index (or > bus and unit instead, where appropriate). > > > and I'm pretty sure that this isn't something that should > > have significance in external interfaces and therefore become a stable > > API. > > I agree that "implied by execution order" is a bad idea: commit > 95fd260f0a "blockdev: Drop unused drive_get_next()".
Ah good, I was indeed thinking of something drive_get_next()-like. In case the board works with explicit indices, the situation is not as bad as I was afraid. It will certainly be workable (even if not obvious) for any boards that have a fixed number of devices with block backends, which should cover everything we're intending to cover here. I still consider if=other a bad user interface because what it means is completely opaque, but if that's okay for you in your board, who am I to object. (Of course, the real solution would be having a generic way to set qdev properties for on-board devices. I'm not expecting that we're getting this anytime soon, though.) Kevin
