[PATCH] ARM: setup_mm_for_reboot(): use flush_cache_louis()

[Will Deacon]

On Tue, Nov 06, 2012 at 10:04:58PM +0000, Russell King - ARM Linux wrote:
> On Tue, Nov 06, 2012 at 04:12:27PM -0500, Nicolas Pitre wrote:
> > 
> > ... instead of flush_cache_all().  The later unconditionally flushes
> > the L2 cache on ARMv7 architectures such as Cortex A15 and A7 which
> > is costly and unnecessary in some scenarios where setup_mm_for_reboot()
> > is used.  If L2 has to be flushed as well, it should already be done
> > separately on other architectures anyway.
> 
> Why does the cost at reboot count?  It's a relatively slow operation as
> it is anyway, because you have to wait for the system to shut down, call
> the boot loader, etc.
> 
> However, the opposite argument is that the state of the L2 _shouldn't_
> matter - except for one small little detail.  Dirty data, which could
> get evicted and overwrite something that matters.  Generally there won't
> be any dirty data in the L2 cache on normal boot, so this is a situation
> which boot loaders probably don't expect.

Wouldn't the L2 flush in this case be included with the code that turns off
caching? For reboot, that's currently done in __sort_restart -- the cache
flush in setup_mm_for_reboot is just to ensure that the idmap tables are
visible to the hardware walker iirc.

Will