linux-kernel - Re: [PATCH] clocksource: mips-gic-timer: fix clocksource counter width

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Message-ID: <alpine.DEB.2.21.1802281025390.1886@nanos.tec.linutronix.de>
Date:   Wed, 28 Feb 2018 10:27:08 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Felix Fietkau <nbd@....name>
cc:     linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org,
        paul.burton@...tec.com
Subject: Re: [PATCH] clocksource: mips-gic-timer: fix clocksource counter
 width

On Wed, 28 Feb 2018, Felix Fietkau wrote:
> On 2018-02-28 09:56, Thomas Gleixner wrote:
> > On Wed, 21 Feb 2018, Felix Fietkau wrote:
> > 
> >> This code needs to use ffs instead of fls on the mask to determine the
> >> shift for reading the GIC_CONFIG_COUNTBITS field.
> > 
> > Why?
> >>  	count_width = read_gic_config() & GIC_CONFIG_COUNTBITS;
> >> -	count_width >>= __fls(GIC_CONFIG_COUNTBITS);
> >> +	count_width >>= __ffs(GIC_CONFIG_COUNTBITS);
> This code is trying to extract the GIC_CONFIG_COUNTBITS field from
> read_gic_config(), so it needs to shift count_width right by the index
> of the least significant bit (__ffs) instead of the most significant bit
> (__fls) of the field mask.

Sure, but that information wants to be in the changelog.

Thanks,

	tglx