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Date: Thu, 09 Jan 2014 19:35:03 +0000
From: Sudeep Holla <Sudeep.Holla@arm.com>
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To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Subject: Re: [PATCH RFC 2/3] ARM: kernel: add support for cpu cache information
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Cc: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
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On 08/01/14 20:57, Russell King - ARM Linux wrote:
> On Wed, Jan 08, 2014 at 07:26:07PM +0000, Sudeep Holla wrote:
>> +#if __LINUX_ARM_ARCH__ < 7 /* pre ARMv7 */
>> +
>> +#define MAX_CACHE_LEVEL=09=091=09/* Only 1 level supported */
>> +#define CTR_CTYPE_SHIFT=09=0924
>> +#define CTR_CTYPE_MASK=09=09(1 << CTR_CTYPE_SHIFT)
>> +
>> +static inline unsigned int get_ctr(void)
>> +{
>> +=09unsigned int ctr;
>> +=09asm volatile ("mrc p15, 0, %0, c0, c0, 1" : "=3Dr" (ctr));
>> +=09return ctr;
>> +}
>> +
>> +static enum cache_type get_cache_type(int level)
>> +{
>> +=09if (level > MAX_CACHE_LEVEL)
>> +=09=09return CACHE_TYPE_NOCACHE;
>> +=09return get_ctr() & CTR_CTYPE_MASK ?
>> +=09=09CACHE_TYPE_SEPARATE : CACHE_TYPE_UNIFIED;
>=20
> 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?
>=20

I assume you referring to some particular CPUs which don't implement this.
I could not find it as optional or IMPLEMENTATION defined in ARM ARM.
I might be missing to find it or there may be exceptions.
Can you please provide more information on that ?

Regards,
Sudeep