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SubjectRE: [PATCH v3 07/10] clocksource/drivers/hyper-v: Handle vDSO differences inline
Date
From: Daniel Lezcano <daniel.lezcano@linaro.org> Sent: Tuesday, March 2, 2021 2:14 PM
>
> On 02/03/2021 22:38, Michael Kelley wrote:
> > While the driver for the Hyper-V Reference TSC and STIMERs is architecture
> > neutral, vDSO is implemented for x86/x64, but not for ARM64. Current code
> > calls into utility functions under arch/x86 (and coming, under arch/arm64)
> > to handle the difference.
> >
> > Change this approach to handle the difference inline based on whether
> > VDSO_CLOCK_MODE_HVCLOCK is present. The new approach removes code under
> > arch/* since the difference is tied more to the specifics of the Linux
> > implementation than to the architecture.
> >
> > No functional change.
> >
> > Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> > Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> > ---
> > arch/x86/include/asm/mshyperv.h | 4 ----
> > drivers/clocksource/hyperv_timer.c | 10 ++++++++--
> > 2 files changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> > index c10dd1c..4f566db 100644
> > --- a/arch/x86/include/asm/mshyperv.h
> > +++ b/arch/x86/include/asm/mshyperv.h
> > @@ -27,10 +27,6 @@ static inline u64 hv_get_register(unsigned int reg)
> > return value;
> > }
> >
> > -#define hv_set_clocksource_vdso(val) \
> > - ((val).vdso_clock_mode = VDSO_CLOCKMODE_HVCLOCK)
> > -#define hv_enable_vdso_clocksource() \
> > - vclocks_set_used(VDSO_CLOCKMODE_HVCLOCK);
> > #define hv_get_raw_timer() rdtsc_ordered()
> >
> > /*
> > diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> > index c73c127..06984fa 100644
> > --- a/drivers/clocksource/hyperv_timer.c
> > +++ b/drivers/clocksource/hyperv_timer.c
> > @@ -370,11 +370,13 @@ static void resume_hv_clock_tsc(struct clocksource *arg)
> > hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
> > }
> >
> > +#ifdef VDSO_CLOCKMODE_HVCLOCK
> > static int hv_cs_enable(struct clocksource *cs)
> > {
> > - hv_enable_vdso_clocksource();
> > + vclocks_set_used(VDSO_CLOCKMODE_HVCLOCK);
> > return 0;
> > }
> > +#endif
>
> We had a confusion here. The suggestion was to remove the #ifdef here
> and add the __maybe_unused annotation to the function.

I wondered if maybe that's what you were getting at with your
most recent comments. But the code doesn't compile on ARM64
with __maybe_unused instead of the #ifdef because
VDSO_CLOCKMODE_HVCLOCK is undefined.

Michael

>
> > static struct clocksource hyperv_cs_tsc = {
> > .name = "hyperv_clocksource_tsc_page",
> > @@ -384,7 +386,12 @@ static int hv_cs_enable(struct clocksource *cs)
> > .flags = CLOCK_SOURCE_IS_CONTINUOUS,
> > .suspend= suspend_hv_clock_tsc,
> > .resume = resume_hv_clock_tsc,
> > +#ifdef VDSO_CLOCKMODE_HVCLOCK
> > .enable = hv_cs_enable,
> > + .vdso_clock_mode = VDSO_CLOCKMODE_HVCLOCK,
> > +#else
> > + .vdso_clock_mode = VDSO_CLOCKMODE_NONE,
> > +#endif
> > };
> >

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