linux-kernel - Re: [RFC PATCH v2 03/14] x86/hpet: Calculate ticks-per-second in a separate function

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Date:   Tue, 26 Mar 2019 22:03:02 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Ashok Raj <ashok.raj@...el.com>,
        Andi Kleen <andi.kleen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Clemens Ladisch <clemens@...isch.de>,
        Arnd Bergmann <arnd@...db.de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH v2 03/14] x86/hpet: Calculate ticks-per-second in a
 separate function

On Wed, 27 Feb 2019, Ricardo Neri wrote:
>  int hpet_alloc(struct hpet_data *hdp)
>  {
>  	u64 cap, mcfg;
> @@ -845,7 +868,6 @@ int hpet_alloc(struct hpet_data *hdp)
>  	size_t siz;
>  	struct hpet __iomem *hpet;
>  	static struct hpets *last;
> -	unsigned long period;
>  	unsigned long long temp;
>  	u32 remainder;
>  
> @@ -881,6 +903,8 @@ int hpet_alloc(struct hpet_data *hdp)
>  
>  	cap = readq(&hpet->hpet_cap);
>  
> +	temp = hpet_get_ticks_per_sec(cap);

Just putting stuff to random places does not make the code any better.

>  	ntimer = ((cap & HPET_NUM_TIM_CAP_MASK) >> HPET_NUM_TIM_CAP_SHIFT) + 1;
>  
>  	if (hpetp->hp_ntimer != ntimer) {
> @@ -897,11 +921,6 @@ int hpet_alloc(struct hpet_data *hdp)
>  
>  	last = hpetp;
>  
> -	period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >>
> -		HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */
> -	temp = 1000000000000000uLL; /* 10^15 femtoseconds per second */
> -	temp += period >> 1; /* round */
> -	do_div(temp, period);
>  	hpetp->hp_tick_freq = temp; /* ticks per second */

What's wrong with the obvious:

       hpetp->hp_tick_freq = hpet_get_ticks_per_sec(cap);

Hmm?

Thanks,

	tglx