[PATCH] ARM: Fix errata 751472 handling on Cortex-A9 r1p*

[Russell King - ARM Linux]

On Wed, Nov 14, 2012 at 02:21:59PM -0800, Tony Lindgren wrote:
> No idea if assuming that zero value for the diagnostic register
> is safe.. What's the default value of the diagnostic register supposed
> to be?

No, that's not safe.  What if your pre-kernel code has asked the secure
monitor to set the work-around bit already?

>  #if defined(CONFIG_ARM_ERRATA_751472) && defined(CONFIG_SMP)
>  	ALT_SMP(cmp r6, #0x30)			@ present prior to r3p0
>  	ALT_UP_B(1f)
> -	mrclt	p15, 0, r10, c15, c0, 1		@ read diagnostic register
> -	orrlt	r10, r10, #1 << 11		@ set bit #11
> -	mcrlt	p15, 0, r10, c15, c0, 1		@ write diagnostic register
> +	bge	1f				@ not needed for r3p0 and later
> +	mrc	p15, 0, r10, c15, c0, 1		@ read diagnostic register
> +	teq	r10, #0				@ zero for secure mode?
> +	beq	1f				@ bail out for secure mode

This test for zero is pointless.  What if some other work-around has
been enabled but not this one?

> +	tst	r10, #1 << 11			@ bit #11 already set?
> +	orreq	r10, r10, #1 << 11		@ set bit #11 if not set
> +	mcreq	p15, 0, r10, c15, c0, 1		@ write diagnostic register
>  1:
>  #endif
>