Re: [PATCH v1 12/15] xen/riscv: introduce sbi_set_timer()

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 1/14/26 10:07 AM, Jan Beulich wrote:
> On 13.01.2026 17:33, Oleksii Kurochko wrote:
> > On 1/12/26 4:12 PM, Jan Beulich wrote:
> > > On 24.12.2025 18:03, Oleksii Kurochko wrote:
> > > > Introduce pointer to function which points to a specific sbi_set_timer()
> > > > implementation. It is done in this way as different OpenSBI version can
> > > > have different Extenion ID and/or funcion ID for TIME extension.
> > > >
> > > > sbi_set_time() programs the clock for next event after stime_value
> > > > time. This function also clears the pending timer interrupt bit.
> > > >
> > > > Introduce extension ID and SBI function ID for TIME extension.
> > > >
> > > > Implement only sbi_set_timer_v02() as there is not to much sense
> > > > to support earlier version and, at the moment, Xen supports only v02.
> > > Besides this somewhat contradicting the use of a function pointer: What
> > > about the legacy extension's equivalent?
> > I think this is not really needed, and the same implementation can be used for
> > both the Legacy and TIME extensions, since the API is identical and the only
> > difference is that|sbi_set_timer()| was moved into a separate extension.
> >
> > Since Xen reports to the guest that it supports SBI v0.2, it is up to the guest
> > implementation to decide why it is still using|sbi_set_timer()| from the
> > Legacy extension instead of the TIME extension.
> >
> > I think that I can add Legacy extension equivalent but considering that we are
> > using OpenSBI v0.2 for which Time extension is available it seems for me it is
> > enough to define sbi_set_timer to sbi_set_timer_v02() for now.
> Feels like here you're negating what just before you wrote in reply to 10/15.
> IOW - I'm now sufficiently confused. (Just consider if you ran Xen itself as
> a guest of the very same Xen. From what you said for 10/15, it would end up
> not seeing the TIME extension as available, hence would need a fallback to
> the Legacy one.
You are right, a fallback to the Legacy one should be provided for such cases.

Actually, it is why Linux could be ran now as it has its fallback too.

~ Oleksii