linux-kernel - Re: [RFC v5 21/23] clockevents: initial support for mono to raw time conversion

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Date:   Sun, 04 Sep 2016 11:50:56 +0200
From:   Nicolai Stange <nicstange@...il.com>
To:     Nicolai Stange <nicstange@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v5 21/23] clockevents: initial support for mono to raw time conversion

Nicolai Stange <nicstange@...il.com> writes:

> +static u32 __clockevents_calc_adjust_freq(u32 mult_ce_raw, u32 mult_cs_mono,
> +					u32 mult_cs_raw)
> +{
> +	u64 adj;
> +	int sign;
> +
> +	if (mult_cs_raw >= mult_cs_mono) {
> +		sign = 0;
> +		adj = mult_cs_raw - mult_cs_mono;
> +	} else {
> +		sign = 1;
> +		adj = mult_cs_mono - mult_cs_raw;
> +	}
> +
> +	adj *= mult_ce_raw;
> +	adj += mult_cs_mono / 2;
> +	do_div(adj, mult_cs_mono);
> +
> +	if (!sign) {
> +		/*
> +		 * Never increase mult by more than 12.5%,
> +		 * c.f. __clockevents_update_bounds().
> +		 */
> +		adj = max_t(u64, adj, mult_ce_raw / 8);

This is wrong and should read as min_t(...), of course -- it's an upper
bound.


> +		if (U32_MAX - mult_ce_raw < adj)
> +			return U32_MAX;
> +		return mult_ce_raw + (u32)adj;
> +	}
> +	if (adj >= mult_ce_raw)
> +		return 1;
> +	return mult_ce_raw - (u32)adj;
> +}