Re: [PATCH v2 14/22] arm64: Cleanup HWCAP handling - Russell King

From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Suzuki K. Poulose" <suzuki.poulose@arm.com>,
	mark.rutland@arm.com, Vladimir.Murzin@arm.com,
	steve.capper@linaro.org, ard.biesheuvel@linaro.org,
	marc.zyngier@arm.com, andre.przywara@arm.com,
	will.deacon@arm.com, linux-kernel@vger.kernel.org,
	edward.nevill@linaro.org, aph@redhat.com, james.morse@arm.com,
	dave.martin@arm.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 14/22] arm64: Cleanup HWCAP handling
Date: Thu, 8 Oct 2015 12:17:09 +0100	[thread overview]
Message-ID: <20151008111709.GE32532@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <20151008111000.GG17192@e104818-lin.cambridge.arm.com>

On Thu, Oct 08, 2015 at 12:10:00PM +0100, Catalin Marinas wrote:
> On Mon, Oct 05, 2015 at 06:02:03PM +0100, Suzuki K. Poulose wrote:
> > +static bool cpus_have_hwcap(const struct arm64_cpu_capabilities *cap)
> > +{
> > +	switch(cap->hwcap_type) {
> > +	case CAP_HWCAP:
> > +		return !!(elf_hwcap & cap->hwcap);
> > +#ifdef CONFIG_COMPAT
> > +	case CAP_COMPAT_HWCAP:
> > +		return !!(compat_elf_hwcap & (u32)cap->hwcap);
> > +	case CAP_COMPAT_HWCAP2:
> > +		return !!(compat_elf_hwcap2 & (u32)cap->hwcap);
> > +#endif
> > +	default:
> > +		BUG();
> > +		return false;
> > +	}
> > +}
> 
> Apart from the multiple returns, you don't really need !! since the
> return type is bool already.

That's wrong.  a & b doesn't return 0 or 1, but the bitwise-and result.

http://yarchive.net/comp/linux/bool.html

especially hpa's response.

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