On 30/04/2024 13:44, Conor Dooley wrote: > 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. Hi Conor, Were you able to discuss that topic ? > > 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. Did you found time to look at the implementation ? Thanks, Clément > > Cheers, > Conor.
