On Wed, 2024-03-20 at 19:44 +0000, Conor Dooley wrote: > IIRC this only "works" because the OpenSBI devs assume that there are > no > non-normative behaviours and all CSRs have their ~God~ RVI defined > meanings. Reading a CSR to see if it traps is not behaviour you can > really > rely on unless the platform claims to support Sstrict - but Sstrict > you'd > have to detect from the DT so chicken and egg for you! It's one of > these > new "extensions" from the profiles spec, so it doesn't even have > support > in Linux's dt-bindings yet. Up to Xen devs if you guys want to make > the > same assumptions as OpenSBI. Linux doesn't and when we discussed this > not too long ago on the U-Boot ML in the context of the rng CSR it > was > also decided not to do make the assumption there either. > > Personally I wonder if you can just apply the same policy here as you > did with Zbb in the other thread and assume that something with H > will > have Zihintpause and leave implementing a "fake" pause as an exercise > for someone that introduces such a system?
If i understand you correctly, then it is done in this way now. Only build time check is done, but it would be nice also have some runtime check, and for now, for runtime the "check" is only exists in booting.txt where it mentioned that Xen expects from CPU to support some extenstions; otherwise "please implement the following functions". Anyway, at the moment, the best one runtime check which we can provide is detect availability of extensions from DT and what I mentioned in commit message. ~ Oleksii
