[PATCH v2] ARM: Do not run dummy_flush_tlb_a15_erratum() on non-Cortex-A15

[Russell King - ARM Linux]

On Wed, Jul 31, 2013 at 11:03:46PM -0500, Rob Herring wrote:
> I just submitted my patch for 798181 ECO fix handling to the patch
> system today. Then I noticed this patch in your fixes branch. This is
> going to cause some churn as my patch needs to move the core version
> check back to a .c file.
> 
> I don't know if you are okay with rebasing your fixes branch or not.
> If my patch is applied first, then this issue can be handled by just
> replacing dummy_flush_tlb_a15_erratum call in context.c a call to
> erratum_a15_798181.

Well, firstly, are you sure your patch is correct?

You're removing the call to dummy_flush_tlb_a15_erratum() before the
smp_call_function() - smp_call_function() does _not_ call the function
for the local CPU.  So, what this means is we don't end up doing any
of the workaround for the local CPU.

Secondly, doesn't the check in your case reduce down to:

	unsigned int midr = read_cpuid_id();

	/* Cortex-A15 r0p0..r3p2 affected */
	if ((midr & 0xff0ffff0) != 0x410fc0f0 || midr > 0x413fc0f2 ||
	    /* ECO not fully fixed */
	    !(read_cpuid(CPUID_REVIDR) & 0x010))
		return 0;
	return 1;

because, assuming midr is not satisfied:

revidr	errata_fix_needed	function return
000	2			1
010	1			0
200	2			1
210	0			0

I think that the above version is still cheap enough to be inline.