linux-kernel - Re: [PATCH v3 07/10] clocksource/drivers/hyper-v: Handle vDSO differences inline

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Message-ID: <25234414-d905-0f9c-af92-9a9e4cde30c4@linaro.org>
Date:   Tue, 2 Mar 2021 23:14:22 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Michael Kelley <mikelley@...rosoft.com>, sthemmin@...rosoft.com,
        kys@...rosoft.com, wei.liu@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, arnd@...db.de,
        linux-hyperv@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v3 07/10] clocksource/drivers/hyper-v: Handle vDSO
 differences inline

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@...rosoft.com>
> Reviewed-by: Boqun Feng <boqun.feng@...il.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.

>  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
>  };
>  
>  static u64 notrace read_hv_clock_msr(void)
> @@ -442,7 +449,6 @@ static bool __init hv_init_tsc_clocksource(void)
>  	tsc_msr = tsc_msr | 0x1 | (u64)phys_addr;
>  	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
>  
> -	hv_set_clocksource_vdso(hyperv_cs_tsc);
>  	clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
>  
>  	hv_sched_clock_offset = hv_read_reference_counter();
> 


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