linux-kernel - Re: [PATCH v3 1/9] clocksource: arm_arch_timer: Gather KVM specific information in a structure

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Date:	Tue, 8 Mar 2016 19:23:43 -0800
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Julien Grall <julien.grall@....com>
Cc:	kvmarm@...ts.cs.columbia.edu, marc.zyngier@....com,
	fu.wei@...aro.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	wei@...hat.com, al.stone@...aro.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 1/9] clocksource: arm_arch_timer: Gather KVM specific
 information in a structure

On Tue, Mar 08, 2016 at 11:29:25AM +0000, Julien Grall wrote:
> Introduce a structure which are filled up by the arch timer driver and
> used by the virtual timer in KVM.
> 
> The first member of this structure will be the timecounter. More members
> will be added later.
> 
> A stub for the new helper isn't introduced because KVM requires the arch
> timer for both ARM64 and ARM32.
> 
> The function arch_timer_get_timecounter is kept for the time being and
> will be dropped in a subsequent patch.
> 
> Signed-off-by: Julien Grall <julien.grall@....com>
> 
> ---
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Marc Zyngier <marc.zyngier@....com>
> 
>     Changes in v3:
>         - Rename the patch
>         - Move the KVM changes and removal of arch_timer_get_timecounter
>         in separate patches.
> ---
>  drivers/clocksource/arm_arch_timer.c | 12 +++++++++---
>  include/clocksource/arm_arch_timer.h |  5 +++++
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index ffe9d1c..b7ab588 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -456,11 +456,16 @@ static struct cyclecounter cyclecounter = {
>  	.mask	= CLOCKSOURCE_MASK(56),
>  };
>  
> -static struct timecounter timecounter;
> +static struct arch_timer_kvm_info arch_timer_kvm_info;
> +
> +struct arch_timer_kvm_info *arch_timer_get_kvm_info(void)

borderline bikeshedding question:

does it make sense that the info the arch timer code exports is labeled
to be kvm-specific?  In other words, could we imagine another subsystem
using this timer info some time and is there a more generic term that
would be more appropriate?


otherwise it looks fine to me.

-Christoffer

> +{
> +	return &arch_timer_kvm_info;
> +}
>  
>  struct timecounter *arch_timer_get_timecounter(void)
>  {
> -	return &timecounter;
> +	return &arch_timer_kvm_info.timecounter;
>  }
>  
>  static void __init arch_counter_register(unsigned type)
> @@ -488,7 +493,8 @@ static void __init arch_counter_register(unsigned type)
>  	clocksource_register_hz(&clocksource_counter, arch_timer_rate);
>  	cyclecounter.mult = clocksource_counter.mult;
>  	cyclecounter.shift = clocksource_counter.shift;
> -	timecounter_init(&timecounter, &cyclecounter, start_count);
> +	timecounter_init(&arch_timer_kvm_info.timecounter,
> +			 &cyclecounter, start_count);
>  
>  	/* 56 bits minimum, so we assume worst case rollover */
>  	sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
> diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h
> index 25d0914..9101ed6b 100644
> --- a/include/clocksource/arm_arch_timer.h
> +++ b/include/clocksource/arm_arch_timer.h
> @@ -49,11 +49,16 @@ enum arch_timer_reg {
>  
>  #define ARCH_TIMER_EVT_STREAM_FREQ	10000	/* 100us */
>  
> +struct arch_timer_kvm_info {
> +	struct timecounter timecounter;
> +};
> +
>  #ifdef CONFIG_ARM_ARCH_TIMER
>  
>  extern u32 arch_timer_get_rate(void);
>  extern u64 (*arch_timer_read_counter)(void);
>  extern struct timecounter *arch_timer_get_timecounter(void);
> +extern struct arch_timer_kvm_info *arch_timer_get_kvm_info(void);
>  
>  #else
>  
> -- 
> 1.9.1
>