Re: [Xen-devel] [RFC PATCH 06/31] cpufreq: make cpufreq driver more generalizable

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 6 Dec 2017, Jan Beulich wrote:
> >>> On 05.12.17 at 21:48, <sstabellini@xxxxxxxxxx> wrote:
> > You are right. We need to define a new struct for internal usage, for
> > example:
> > 
> > struct xen_processor_performance_internal {
> >     uint32_t flags;     /* flag for Px sub info type */
> >     uint32_t platform_limit;  /* Platform limitation on freq usage */
> >     struct xen_pct_register control_register;
> >     struct xen_pct_register status_register;
> >     uint32_t state_count;     /* total available performance states */
> >     struct xen_processor_px states;
> >     struct xen_psd_package domain_info;
> >     uint32_t shared_type;     /* coordination type of this processor */
> > };
> > 
> > Jan, Andrew, does this sound like a good approach to you?
> 
> I'm afraid I don't have the time to go through this discussion (and
> the original patch) in detail to figure out the full context in which
> you raise the question. IOW please summarize things alongside
> the proposed structure, or alternatively Oleksandr could simply
> submit an updated patch to allow seeing the actual context
> (albeit in any case I can't promise timely feedback, given the
> number of pending patches plus all the work I still hope to be
> able to get done myself eventually.
> 
> >From a brief check, I can't really figure much of a difference to
> the already existing (and internal) struct processor_performance.

Fair enough. Actually you have a good eye for being able to spot your
name in one of so many patch replies :-)


Oleksandr would like to call set_px_pminfo from a non-hypercall context,
meaning that there are no XEN_GUEST_HANDLE parameters. Today, struct
xen_processor_performance contains a

  XEN_GUEST_HANDLE(xen_processor_px_t) states;

field. Instead of "faking" the XEN_GUEST_HANDLE field from Xen, I
suggested to modify set_px_pminfo to take a different struct, one
without any XEN_GUEST_HANDLE field. For example:

 struct xen_processor_performance_internal {
     uint32_t flags;     /* flag for Px sub info type */
     uint32_t platform_limit;  /* Platform limitation on freq usage */
     struct xen_pct_register control_register;
     struct xen_pct_register status_register;
     uint32_t state_count;     /* total available performance states */
     struct xen_processor_px states;   <---- this is the interesting change
     struct xen_psd_package domain_info;
     uint32_t shared_type;     /* coordination type of this processor */
 };

The caller, in the x86 case is
xen/arch/x86/platform_hypercall.c:do_platform_op, would be resposible
for issuing the copy_from_guest.

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