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

Sughosh Ganu
2013-07-08T14:07:22Z

hi Albert,

On Mon Jul 08, 2013 at 02:32:16PM +0200, Albert ARIBAUD wrote:
> Hi Sughosh,
>
> On Mon, 8 Jul 2013 17:38:46 +0530, Sughosh Ganu
> <urwithsughosh@gmail.com> wrote:
>
> > hi Albert,
> > On Mon Jul 08, 2013 at 12:22:57PM +0200, Albert ARIBAUD wrote:
> >
> > <snip>
> >
> > > It you flush first then disable, you leave a time window between the
> > > two where a write to the cache can happen (either because your code
> > > does one, or because the compiler optimized one in). If it happens,
> > > then you disable a cache which is still dirty -- IOW, your flushing
> > > has failed its mission, and your cache and memory are still not
> > > coherent.
> >
> > Since this is specific to arm926ejs, can we not flush *and* invalidate
> > the dcache before disabling it -- since the arm926ejs cache uses a
> > read allocate policy, flushing and invalidating a cache before
> > disabling it would not result in the cache getting written to in the
> > window that you refer to. Also, flushing and cleaning is an atomic
> > operation.
>
> 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.

-sughosh