[U-Boot] [PATCH 1/5] ARM: cache: Move the cp15 CR register read before flushing the cache.

[Marek Vasut]

Dear Sricharan R,

> Ping..

+1

> Thanks,
>  Sricharan
> 
> > -----Original Message-----
> > From: R, Sricharan [mailto:r.sricharan at ti.com]
> > Sent: Tuesday, May 29, 2012 8:24 PM
> > To: U-Boot at lists.denx.de; albert.u.boot at aribaud.net
> > Cc: trini at ti.com
> > Subject: Re: [U-Boot] [PATCH 1/5] ARM: cache: Move the cp15 CR register
> > read before flushing the cache.
> > 
> > Hi Albert,
> > 
> >   Are you planning to take up the below patch ?
> > 
> > Thanks,
> > 
> >  Sricharan
> > 
> > On Thu, May 17, 2012 at 3:22 PM, R Sricharan <r.sricharan at ti.com>
> > 
> > wrote:
> > > The following is the cleanup sequence in arch/arm/cpu/armv7/cpu.c
> > > 
> > > int cleanup_before_linux(void)
> > > {
> > >  ...
> > >  ...
> > >  dcache_disable();
> > >  v7_outer_cache_disable();
> > >  invalidate_dcache_all();
> > > }
> > > 
> > >  1) invalidate_dcache_all call expects that all the caches has been
> > >  flushed, invalidated and there are no dirty entries prior to its
> > >  execution.  In the above sequence dcache_disable() flushes,
> > 
> > invalidates
> > 
> > >  the caches and turns off the  mmu. But after it cleanups the cache
> > >  and before the mmu is disabled  there is a cp_delay() function which
> > >  has STR instruction. On certain cores like the cortex-a15, cache hit
> > >  and a write can happen to a cache line even when the dcache is
> > >  disabled. So the above mentioned STR instruction creates a dirty
> > 
> > entry
> > 
> > >  after cleaning. The mmu gets disabled after this.
> > > 
> > >  2) invalidate_dcache_all invalidates the cache lines. Again on
> > >  cores like cortex-a15, invalidate instruction flushes the dirty
> > >  line as well. So some times the dirty line from sequence 1
> > >  can corrupt the memory resulting in a crash.
> > > 
> > >  Fixing this by moving the get_cr() and cp_delay() calls before
> > >  cleaning up the cache, thus avoiding the dirty entry.
> > > 
> > > Signed-off-by: R Sricharan <r.sricharan at ti.com>
> > > ---
> > >  arch/arm/lib/cache-cp15.c |    6 +++---
> > >  1 files changed, 3 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/arch/arm/lib/cache-cp15.c b/arch/arm/lib/cache-cp15.c
> > > index e6c3eae..939de10 100644
> > > --- a/arch/arm/lib/cache-cp15.c
> > > +++ b/arch/arm/lib/cache-cp15.c
> > > @@ -115,17 +115,17 @@ static void cache_disable(uint32_t cache_bit)
> > >  {
> > >        uint32_t reg;
> > > 
> > > +       reg = get_cr();
> > > +       cp_delay();
> > > +
> > >        if (cache_bit == CR_C) {
> > >                /* if cache isn;t enabled no need to disable */
> > > -               reg = get_cr();
> > >                if ((reg & CR_C) != CR_C)
> > >                        return;
> > >                /* if disabling data cache, disable mmu too */
> > >                cache_bit |= CR_M;
> > >                flush_dcache_all();
> > >        }
> > > -       reg = get_cr();
> > > -       cp_delay();
> > >        set_cr(reg & ~cache_bit);
> > >  }
> > >  #endif
> > > --
> > > 1.7.1
> > > 
> > > _______________________________________________
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> > > U-Boot at lists.denx.de
> > > http://lists.denx.de/mailman/listinfo/u-boot
> 
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Best regards,
Marek Vasut