[U-Boot] [RFC PATCH] arm: arm926ejs: flush cache before disable it

[Sughosh Ganu <urwithsughosh@gmail.com>]

hi Albert,

On Mon Jul 08, 2013 at 09:55:51PM +0200, Albert ARIBAUD wrote:

<snip>

> > > Invalidating the cache in addition to flushing it would not prevent
> > > further writes from dirtying the cache lines if they happen before
> > > the cache is disabled.
> > 
> > I have a doubt on this. The arm926ejs uses a read-allocate policy,
> > wherein a new cache line is allocated only on a read miss -- a write
> > to an address not present in the cache gets written to memory. So if
> > the cache line is invalidated, how will data get written to the cache.
> 
> The arm926ej-s data cache does not have a single fixed policy, and
> does not have a bypass-on-write policy, only write-through and
> copy-back.
> 
> Other, more complex, policies may be defined, but at the MMU, not cache,
> level, and those are not constant for all arm926ej-s based SoCs; not
> even constant for a given SoC as they are configurable at run-time to
> fit the chosen system addressing map.

Can you please elucidate on these policies. Based on my reading of the
arm developers manual and the arm926ejs trm, the mmu makes a
particular region cacheable and/or write bufferable. I did not find
mention of any other  policies. Maybe pointers or links to the
documents would help.

> (Besides, bypassing the cache for writes and not reads is of little
> interest for plain DDR caching.)

Again, this is independent of the target interface that is being
cached(if i've missed something, can you please point me to the
document). Thanks.

-sughosh