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

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Date:   Mon, 8 Mar 2021 15:41:46 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: Re: [PATCH v3 07/10] clocksource/drivers/hyper-v: Handle vDSO
 differences inline

On 08/03/2021 14:49, Michael Kelley wrote:
> From: Michael Kelley <mikelley@...rosoft.com> Sent: Tuesday, March 2, 2021 3:07 PM
>>
>> From: Daniel Lezcano <daniel.lezcano@...aro.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@...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.
>>
>> 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
>>
> 
> Daniel -- any additional comments/feedback?  Getting your Ack on
> this patch should be the last step to wrap up the patch series.

It would have been nice to simplify those #ifdef but I don't see a
straightforward change for that... :(

Acked-by: Daniel Lezcano <daniel.lezcano@...aro.org>



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