On Tue, Apr 30, 2024 at 09:18:47AM +0200, Clément Léger wrote: > > > On 30/04/2024 00:15, Conor Dooley wrote: > > On Mon, Apr 29, 2024 at 05:04:55PM +0200, Clément Léger wrote: > >> Since a few extensions (Zicbom/Zicboz) already needs validation and > >> future ones will need it as well (Zc*) add a validate() callback to > >> struct riscv_isa_ext_data. This require to rework the way extensions are > >> parsed and split it in two phases. First phase is isa string or isa > >> extension list parsing and consists in enabling all the extensions in a > >> temporary bitmask without any validation. The second step "resolves" the > >> final isa bitmap, handling potential missing dependencies. The mechanism > >> is quite simple and simply validate each extension described in the > >> temporary bitmap before enabling it in the final isa bitmap. validate() > >> callbacks can return either 0 for success, -EPROBEDEFER if extension > >> needs to be validated again at next loop. A previous ISA bitmap is kept > >> to avoid looping mutliple times if an extension dependencies are never > >> satisfied until we reach a stable state. In order to avoid any potential > >> infinite looping, allow looping a maximum of the number of extension we > >> handle. Zicboz and Zicbom extensions are modified to use this validation > >> mechanism. > > > > Your reply to my last review only talked about part of my comments, > > which is usually what you do when you're gonna implement the rest, but > > you haven't. > > I like the change you've made to shorten looping, but I'd at least like > > a response to why a split is not worth doing :) > > Hi Conor, > > Missed that point since I was feeling that my solution actually > addresses your concerns. Your argument was that there is no reason to > loop for Zicbom/Zicboz but that would also apply to Zcf in case we are > on RV64 as well (since zcf is not supported on RV64). So for Zcf, that > would lead to using both mecanism or additional ifdefery with little to > no added value since the current solution actually solves both cases: > > - We don't have any extra looping if all validation callback returns 0 > (except the initial one on riscv_isa_ext, which is kind of unavoidable). > - Zicbom, Zicboz callbacks will be called only once (which was one of > your concern). > > Adding a second kind of callback for after loop validation would only > lead to a bunch of additional macros/ifdefery for extensions with > validate() callback, with validate_end() or with both (ie Zcf)). For > these reasons, I do not think there is a need for a separate mechanism > nor additional callback for such extensions except adding extra code > with no real added functionality. > > AFAIK, the platform driver probing mechanism works the same, the probe() > callback is actually called even if for some reason properties are > missing from nodes for platform devices and thus the probe() returns > -EINVAL or whatever. > > Hope this answers your question, Yeah, pretty much I am happy with just an "it's not worth doing it" response. Given it wasn't your first choice, I doubt you're overly happy with it either, but I really would like to avoid looping to closure to sort out dependencies - particularly on the boot CPU before we bring anyone else up, but if the code is now more proactive about breaking out, I suppose that'll have to do :) I kinda wish we didn't do this at all, but I think we've brought this upon ourselves via hwprobe. I'm still on the fence as to whether things that are implied need to be handled in this way. I think I'll bring this up tomorrow at the weekly call, because so far it's only been you and I discussing this really and it's a policy decision that hwprobe-ists should be involved in I think. Implied extensions aside, I think we will eventually need this stuff anyway, for extensions that make no sense to consider if a config option for a dependency is disabled. From talking to Eric Biggers the other week about riscv_isa_extension_available() I'm of the opinion that we need to do better with that interface w.r.t. extension and config dependencies, and what seems like a good idea to me at the moment is putting tests for IS_ENABLED(RISCV_ISA_FOO) into these validate hooks. I'll try to look at the actual implementation here tomorrow. Cheers, Conor.
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