linux-kernel - Re: [PATCH RFC 2/3] ARM: kernel: add support for cpu cache information

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Message-ID: <20140108205754.GN27432@n2100.arm.linux.org.uk>
Date:	Wed, 8 Jan 2014 20:57:54 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Rob Herring <robh@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH RFC 2/3] ARM: kernel: add support for cpu cache
	information

On Wed, Jan 08, 2014 at 07:26:07PM +0000, Sudeep Holla wrote:
> +#if __LINUX_ARM_ARCH__ < 7 /* pre ARMv7 */
> +
> +#define MAX_CACHE_LEVEL		1	/* Only 1 level supported */
> +#define CTR_CTYPE_SHIFT		24
> +#define CTR_CTYPE_MASK		(1 << CTR_CTYPE_SHIFT)
> +
> +static inline unsigned int get_ctr(void)
> +{
> +	unsigned int ctr;
> +	asm volatile ("mrc p15, 0, %0, c0, c0, 1" : "=r" (ctr));
> +	return ctr;
> +}
> +
> +static enum cache_type get_cache_type(int level)
> +{
> +	if (level > MAX_CACHE_LEVEL)
> +		return CACHE_TYPE_NOCACHE;
> +	return get_ctr() & CTR_CTYPE_MASK ?
> +		CACHE_TYPE_SEPARATE : CACHE_TYPE_UNIFIED;

So, what do we do for CPUs that don't implement the CTR?  Just return
random rubbish based on decoding the CPU Identity register as if it
were the cache type register?

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