| Message ID | 20240329-dev-maxh-lin-452-6-9-v1-2-1534f93b94a7@sifive.com (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | riscv: support Sdtrig extension hcontext/scontext CSRs | expand |
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? Thanks, Conor. > > Signed-off-by: Max Hsu <max.hsu@sifive.com> > --- > Documentation/devicetree/bindings/riscv/cpus.yaml | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml > index d87dd50f1a4b..c713a48c5025 100644 > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml > @@ -137,6 +137,24 @@ properties: > DMIPS/MHz, relative to highest capacity-dmips-mhz > in the system. > > + debug: > + type: object > + properties: > + compatible: > + const: riscv,debug-v1.0.0 > + trigger-module: > + type: object > + description: | > + An indication set of optional CSR existence from > + riscv-debug-spec Sdtrig extension > + properties: > + mcontext-present: > + type: boolean > + hcontext-present: > + type: boolean > + scontext-present: > + type: boolean > + > anyOf: > - required: > - riscv,isa > > -- > 2.43.2 >
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. Thanks, drew > > Thanks, > Conor. > > > > > Signed-off-by: Max Hsu <max.hsu@sifive.com> > > --- > > Documentation/devicetree/bindings/riscv/cpus.yaml | 18 ++++++++++++++++++ > > 1 file changed, 18 insertions(+) > > > > diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml > > index d87dd50f1a4b..c713a48c5025 100644 > > --- a/Documentation/devicetree/bindings/riscv/cpus.yaml > > +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml > > @@ -137,6 +137,24 @@ properties: > > DMIPS/MHz, relative to highest capacity-dmips-mhz > > in the system. > > > > + debug: > > + type: object > > + properties: > > + compatible: > > + const: riscv,debug-v1.0.0 > > + trigger-module: > > + type: object > > + description: | > > + An indication set of optional CSR existence from > > + riscv-debug-spec Sdtrig extension > > + properties: > > + mcontext-present: > > + type: boolean > > + hcontext-present: > > + type: boolean > > + scontext-present: > > + type: boolean > > + > > anyOf: > > - required: > > - riscv,isa > > > > -- > > 2.43.2 > > > -- > kvm-riscv mailing list > kvm-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/kvm-riscv
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!
diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml index d87dd50f1a4b..c713a48c5025 100644 --- a/Documentation/devicetree/bindings/riscv/cpus.yaml +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml @@ -137,6 +137,24 @@ properties: DMIPS/MHz, relative to highest capacity-dmips-mhz in the system. + debug: + type: object + properties: + compatible: + const: riscv,debug-v1.0.0 + trigger-module: + type: object + description: | + An indication set of optional CSR existence from + riscv-debug-spec Sdtrig extension + properties: + mcontext-present: + type: boolean + hcontext-present: + type: boolean + scontext-present: + type: boolean + anyOf: - required: - riscv,isa
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. Signed-off-by: Max Hsu <max.hsu@sifive.com> --- Documentation/devicetree/bindings/riscv/cpus.yaml | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)