linux-kernel - Re: [PATCH] microblaze/timer: set ->min_delta_ticks and ->max_delta

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Message-ID: <20170407131429.GD2078@mai>
Date:   Fri, 7 Apr 2017 15:14:29 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Nicolai Stange <nicstange@...il.com>
Cc:     Michal Simek <monstr@...str.eu>,
        John Stultz <john.stultz@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] microblaze/timer: set ->min_delta_ticks and
 ->max_delta_ticks

On Thu, Mar 30, 2017 at 09:45:28PM +0200, Nicolai Stange wrote:
> In preparation for making the clockevents core NTP correction aware,
> all clockevent device drivers must set ->min_delta_ticks and
> ->max_delta_ticks rather than ->min_delta_ns and ->max_delta_ns: a
> clockevent device's rate is going to change dynamically and thus, the
> ratio of ns to ticks ceases to stay invariant.
> 
> Make the microblaze arch's clockevent driver initialize these fields
> properly.
> 
> This patch alone doesn't introduce any change in functionality as the
> clockevents core still looks exclusively at the (untouched) ->min_delta_ns
> and ->max_delta_ns. As soon as this has changed, a followup patch will
> purge the initialization of ->min_delta_ns and ->max_delta_ns from this
> driver.
> 
> Signed-off-by: Nicolai Stange <nicstange@...il.com>
> ---
> 
> Notes:
>     This prerequisite patch is part of a larger effort to feed NTP
>     corrections into the clockevent devices' frequencies and thus
>     avoiding their notion of time to diverge from the system's
>     one. If you're interested, the current state of the whole series
>     can be found at [1].
>     
>     If you haven't got any objections and these prerequisites get
>     merged by 4.12 everywhere, I'll proceed with the remainder of
>     this series in 4.13.
>     
>     Applicable to next-20170324 as well as to John' Stultz tree [2].
>     
>     [1]
>       git://nicst.de/linux.git cev-freq-adj.v10.fortglx-4.12-time
>       https://nicst.de/git/?p=linux.git;a=shortlog;h=refs/heads/cev-freq-adj.v10.fortglx-4.12-time
>     
>     [2]
>       https://git.linaro.org/people/john.stultz/linux.git fortglx/4.12/time
> 
>  arch/microblaze/kernel/timer.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/microblaze/kernel/timer.c b/arch/microblaze/kernel/timer.c
> index 999066192715..545ccd46edb3 100644
> --- a/arch/microblaze/kernel/timer.c
> +++ b/arch/microblaze/kernel/timer.c
> @@ -178,8 +178,10 @@ static __init int xilinx_clockevent_init(void)
>  				clockevent_xilinx_timer.shift);
>  	clockevent_xilinx_timer.max_delta_ns =
>  		clockevent_delta2ns((u32)~0, &clockevent_xilinx_timer);
> +	clockevent_xilinx_timer.max_delta_ticks = (u32)~0;

Can you take the opportunity to fix the type (unsigned long) ?

>  	clockevent_xilinx_timer.min_delta_ns =
>  		clockevent_delta2ns(1, &clockevent_xilinx_timer);
> +	clockevent_xilinx_timer.min_delta_ticks = 1;
>  	clockevent_xilinx_timer.cpumask = cpumask_of(0);
>  	clockevents_register_device(&clockevent_xilinx_timer);
>  
> -- 
> 2.12.0
> 

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