On Fri, Apr 05, 2024 at 05:59:41PM +0200, Andrew Jones wrote: > On Fri, Mar 29, 2024 at 10:31:10AM +0000, Conor Dooley wrote: > > On Fri, Mar 29, 2024 at 05:26:18PM +0800, Max Hsu wrote: > > > The mcontext/hcontext/scontext CSRs are optional in the Sdtrig extension, > > > to prevent RW operations to the missing CSRs, which will cause > > > illegal instructions. > > > > > > As a solution, we have proposed the dt format for these CSRs. > > > > As I mentioned in your other patch, I amn't sure what the actual value > > is in being told about "sdtrig" itself if so many of the CSRs are > > optional. I think we should define pseudo extensions that represent > > usable subsets that are allowed by riscv,isa-extensions, such as > > those you describe here: sdtrig + mcontext, sdtrig + scontext and > > sdtrig + hcontext. Probably also for strig + mscontext. What > > additional value does having a debug child node give us that makes > > it worth having over something like the above? > > Yeah, Sdtrig, which doesn't tell you what you get, isn't nice at all. > I wonder if we can start with requiring Sdtrig to be accompanied by > Ssstrict in order to enable the context CSRs, i.e. > > Sdtrig - support without optional CSRs > Sdtrig+Ssstrict - probe for optional CSRs, support what's found > > If there are platforms with Sdtrig and optional CSRs, but not Ssstrict, > then maybe the optional CSRs can be detected in some vendor-specific way, > where the decision as to whether or not that vendor-specific way is > acceptable is handled case-by-case. I think it's pretty reasonable to make sstrict a requirement for the kernel's use of sdtrig. If we have some non-sstrict systems that do implement these particular CSRs, then I guess we can add some psuedo instructions then (and nothing would stop the sstrict systems also specifying directly). If they're using some non-standard CSRs then case-by-case I guess. I'm just specifically not keen on adding extra dt properties that do things we can already do with the ones we have!
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