Re: [PATCH] ARM: v7 setup function should invalidate L1 cache

[Shawn Guo <shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Tue, May 19, 2015 at 05:12:56PM +0100, Russell King wrote:
> All ARMv5 and older CPUs invalidate their caches in the early assembly
> setup function, prior to enabling the MMU.  This is because the L1
> cache should not contain any data relevant to the execution of the
> kernel at this point; all data should have been flushed out to memory.
> 
> This requirement should also be true for ARMv6 and ARMv7 CPUs - indeed,
> these typically do not search their caches when caching is disabled (as
> it needs to be when the MMU is disabled) so this change should be safe.
> 
> ARMv7 allows there to be CPUs which search their caches while caching is
> disabled, and it's permitted that the cache is uninitialised at boot;
> for these, the architecture reference manual requires that an
> implementation specific code sequence is used immediately after reset
> to ensure that the cache is placed into a sane state.  Such
> functionality is definitely outside the remit of the Linux kernel, and
> must be done by the SoC's firmware before _any_ CPU gets to the Linux
> kernel.
> 
> Changing the data cache clean+invalidate to a mere invalidate allows us
> to get rid of a lot of platform specific hacks around this issue for
> their secondary CPU bringup paths - some of which were buggy.
> 
> Signed-off-by: Russell King <rmk+kernel-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
> ---
...
>  arch/arm/mach-imx/headsmp.S           |  1 -

Acked-by: Shawn Guo <shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>