Re: [PATCH v3 02/23] psci: Accessor for configured PSCI function IDs

David Brazdil
2020-11-26T17:29:51Z

Hey Mark,

On Thu, Nov 26, 2020 at 05:24:50PM +0000, Mark Rutland wrote:
> On Thu, Nov 26, 2020 at 03:54:00PM +0000, David Brazdil wrote:
> > Function IDs used by PSCI are configurable for v0.1 via DT/APCI. If the
> > host is using PSCI v0.1, KVM's host PSCI proxy needs to use the same IDs.
> > Expose the array holding the information with a read-only accessor.
> >
> > Signed-off-by: David Brazdil <dbrazdil@google.com>
> > ---
> > drivers/firmware/psci/psci.c | 16 ++++++++--------
> > include/linux/psci.h | 10 ++++++++++
> > 2 files changed, 18 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> > index 213c68418a65..40609564595e 100644
> > --- a/drivers/firmware/psci/psci.c
> > +++ b/drivers/firmware/psci/psci.c
> > @@ -58,16 +58,16 @@ typedef unsigned long (psci_fn)(unsigned long, unsigned long,
> > unsigned long, unsigned long);
> > static psci_fn *invoke_psci_fn;
> >
> > -enum psci_function {
> > - PSCI_FN_CPU_SUSPEND,
> > - PSCI_FN_CPU_ON,
> > - PSCI_FN_CPU_OFF,
> > - PSCI_FN_MIGRATE,
> > - PSCI_FN_MAX,
> > -};
> > -
> > static u32 psci_function_id[PSCI_FN_MAX];
> >
> > +u32 psci_get_function_id(enum psci_function fn)
> > +{
> > + if (WARN_ON_ONCE(fn < 0 || fn >= PSCI_FN_MAX))
> > + return 0;
> > +
> > + return psci_function_id[fn];
> > +}
>
> I'd really like if we could namespace this with a psci_0_1_* prefix
> before we expose it outside of the PSCI code. I appreciate that's a
> larger change, but I reckon we only need a couple of new patches:
>
> 1) Split the ops which consume the FN ids into separate psci_0_1_*() and
> psci_0_2_*() variants, with a common __psci_*() helper that takes the
> function ID as an argument. The 0_1 variants would read the function
> ID from a variable, and the 0_2 variants would hard-code the id.
>
> 2) Replace the psci_function_id array with:
>
> struct psci_0_1_function_ids {
> u32 suspend;
> u32 cpu_on;
> u32 cpu_off;
> u32 migrate;
> };
>
> ... and remove enum psci_function entirely.
>
> 3) Add a helper which returns the entire psci_0_1_function_ids struct in
> one go. No warnings necessary.
>
> Does that sound OK to you?

Sure, sounds easy enough and 2) is in line with how I structured the handlers
in KVM.

Thanks,
David