On 21/06/2024 12:17, Conor Dooley wrote:
On Fri, Jun 21, 2024 at 10:37:21AM +0200, Alexandre Ghiti wrote:
On 20/06/2024 08:25, Anup Patel wrote:
On Wed, Jun 5, 2024 at 10:25 PM Conor Dooley <conor@xxxxxxxxxx> wrote:
On Wed, Jun 05, 2024 at 08:15:08PM +0800, Yong-Xuan Wang wrote:
Add entries for the Svade and Svadu extensions to the riscv,isa-extensions
property.
Signed-off-by: Yong-Xuan Wang <yongxuan.wang@xxxxxxxxxx>
---
.../devicetree/bindings/riscv/extensions.yaml | 30 +++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/Documentation/devicetree/bindings/riscv/extensions.yaml b/Documentation/devicetree/bindings/riscv/extensions.yaml
index 468c646247aa..1e30988826b9 100644
--- a/Documentation/devicetree/bindings/riscv/extensions.yaml
+++ b/Documentation/devicetree/bindings/riscv/extensions.yaml
@@ -153,6 +153,36 @@ properties:
ratified at commit 3f9ed34 ("Add ability to manually trigger
workflow. (#2)") of riscv-time-compare.
+ - const: svade
+ description: |
+ The standard Svade supervisor-level extension for raising page-fault
+ exceptions when PTE A/D bits need be set as ratified in the 20240213
+ version of the privileged ISA specification.
+
+ Both Svade and Svadu extensions control the hardware behavior when
+ the PTE A/D bits need to be set. The default behavior for the four
+ possible combinations of these extensions in the device tree are:
+ 1. Neither svade nor svadu in DT: default to svade.
I think this needs to be expanded on, as to why nothing means svade.
Actually if both Svade and Svadu are not present in DT then
it is left to the platform and OpenSBI does nothing.
+ 2. Only svade in DT: use svade.
That's a statement of the obvious, right?
+ 3. Only svadu in DT: use svadu.
This is not relevant for Svade.
+ 4. Both svade and svadu in DT: default to svade (Linux can switch to
+ svadu once the SBI FWFT extension is available).
"The privilege level to which this devicetree has been provided can switch to
Svadu if the SBI FWFT extension is available".
+ - const: svadu
+ description: |
+ The standard Svadu supervisor-level extension for hardware updating
+ of PTE A/D bits as ratified at commit c1abccf ("Merge pull request
+ #25 from ved-rivos/ratified") of riscv-svadu.
+
+ Both Svade and Svadu extensions control the hardware behavior when
+ the PTE A/D bits need to be set. The default behavior for the four
+ possible combinations of these extensions in the device tree are:
@Anup/Drew/Alex, are we missing some wording in here about it only being
valid to have Svadu in isolation if the provider of the devicetree has
actually turned on Svadu? The binding says "the default behaviour", but
it is not the "default" behaviour, the behaviour is a must AFAICT. If
you set Svadu in isolation, you /must/ have turned it on. If you set
Svadu and Svade, you must have Svadu turned off?
Yes, the wording should be more of requirement style using
must or may.
How about this ?
1) Both Svade and Svadu not present in DT => Supervisor may
assume Svade to be present and enabled or it can discover
based on mvendorid, marchid, and mimpid.
2) Only Svade present in DT => Supervisor must assume Svade
to be always enabled. (Obvious)
3) Only Svadu present in DT => Supervisor must assume Svadu
to be always enabled. (Obvious)
I agree with all of that, but the problem is how can we guarantee that
openSBI actually enabled svadu?
Conflation of an SBI implementation and OpenSBI aside, if the devicetree
property is defined to mean that "the supervisor must assume svadu to be
always enabled", then either it is, or the firmware's description of the
hardware is broken and it's not the supervisor's problem any more. It's
not the kernel's job to validate that the devicetree matches the
hardware.
This is not the case for now.
What "is not the case for now"? My understanding was that, at the
moment, nothing happens with Svadu in OpenSBI. In turn, this means that
there should be no devicetrees containing Svadu (per this binding's
description) and therefore no problem?
What prevents a dtb to be passed with svadu to an old version of opensbi
which does not support the enablement of svadu? The svadu extension will
end up being present in the kernel but not enabled right?
Sorry if I'm completely off here, it really feels like I missed something :)
Thanks,
Conor.
