arm: Add ARM ERRATA 775420 workaround

[jungseung lee]

Hi,

I have question the work-around code.
The below code will be enter after handling exception handling path. (that
is fix-up code)
As far as i know, the dsb instruction should be inserted before the any isb
instruction on exception handling code for breaking erratum condition .
It could meet the requirement?

> source "arch/arm/common/Kconfig"
> > diff --git a/arch/arm/mm/cache-v7.S b/arch/arm/mm/cache-v7.S
> > index 39e3fb3..3b17227 100644
> > --- a/arch/arm/mm/cache-v7.S
> > +++ b/arch/arm/mm/cache-v7.S
> > @@ -211,6 +211,9 @@ ENTRY(v7_coherent_user_range)
> >   * isn't mapped, fail with -EFAULT.
> >   */
> > 9001:
> > +#ifdef CONFIG_ARM_ERRATA_775420
> > + dsb
> > +#endif
> >   mov r0, #-EFAULT
> >   mov pc, lr
> >   UNWIND(.fnend )
> >
> >
> thanks
>
> > On Thu, Sep 20, 2012 at 10:58:53AM +0100, Catalin Marinas wrote:
> > > On 12 September 2012 08:14, Simon Horman wrote:
> > > > +config ARM_ERRATA_775420
> > > > +       bool "ARM errata: A data cache maintenance operation which
aborts, might lead to deadlock"
> > > > +       depends on CPU_V7
> > > > +       help
> > > > +         This option enables the workaround for the 775420
Cortex-A9 (r2p2,
> > > > +         r2p6,r2p8,r2p10,r3p0) erratum. In case a date cache
maintenance
> > > > +         operation aborts with MMU exception, it might cause the
processor
> > > > +         deadlock. This workaround puts DSB before executing ISB
at the
> > > > +         beginning of the abort exception handler.
> > > > +
> > > >  endmenu
> > >
> > > The only case where we can get an abort on cache maintenance is
> > > v7_coherent_user_range(). I don't think we have any ISB on the
> > > exception handling path for this function, so we could just add the
> > > DSB there:
> >
> > I think that an advantage of Abe-san's implementation is that
> > it might to be a bit more robust. But your proposal is certainly
> > much cleaner and for that reason I agree it is a good option.
> >
> > I've updated the patch, but since the code is now all yours
> > I'm unsure if the author should be changed or not.
> >
> > ----------------------------------------------------------------
> > From: Kouei Abe
> >
> > arm: Add ARM ERRATA 775420 workaround
> >
> > Workaround for the 775420 Cortex-A9 (r2p2, r2p6,r2p8,r2p10,r3p0)
erratum.
> > In case a date cache maintenance operation aborts with MMU exception, it
> > might cause the processor to deadlock. This workaround puts DSB before
> > executing ISB if an abort may occur on cache maintenance.
> >
> > Based on work by Kouei Abe and feedback from Catalin Marinas.
> >
> > Cc: Catalin Marinas
> > Signed-off-by: Kouei Abe
> > Signed-off-by: Simon Horman
> >
> > ---
> >
> > v2
> > * Add some details to changelog entry
> > * Alternate implementation suggested by Catalin Marinas
> >   - Add the dsb directly to v7_coherent_user_range() rather
> >     than the exception handler
> > ---
> > arch/arm/Kconfig       |   10 ++++++++++
> > arch/arm/mm/cache-v7.S |    3 +++
> > 2 files changed, 13 insertions(+)
> >
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index 2f88d8d..48c19d4 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -1413,6 +1413,16 @@ config PL310_ERRATA_769419
> >    on systems with an outer cache, the store buffer is drained
> >    explicitly.
> >
> > +config ARM_ERRATA_775420
> > +       bool "ARM errata: A data cache maintenance operation which
aborts, might lead to deadlock"
> > +       depends on CPU_V7
> > +       help
> > + This option enables the workaround for the 775420 Cortex-A9 (r2p2,
> > + r2p6,r2p8,r2p10,r3p0) erratum. In case a date cache maintenance
> > + operation aborts with MMU exception, it might cause the processor
> > + to deadlock. This workaround puts DSB before executing ISB if
> > + an abort may occur on cache maintenance.
> > +
> > endmenu
> >
> > source "arch/arm/common/Kconfig"
> > diff --git a/arch/arm/mm/cache-v7.S b/arch/arm/mm/cache-v7.S
> > index 39e3fb3..3b17227 100644
> > --- a/arch/arm/mm/cache-v7.S
> > +++ b/arch/arm/mm/cache-v7.S
> > @@ -211,6 +211,9 @@ ENTRY(v7_coherent_user_range)
> >   * isn't mapped, fail with -EFAULT.
> >   */
> > 9001:
> > +#ifdef CONFIG_ARM_ERRATA_775420
> > + dsb
> > +#endif
> >   mov r0, #-EFAULT
> >   mov pc, lr
> >   UNWIND(.fnend )
> > --
> > 1.7.10.4
> >
> >
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20121107/5e13cf89/attachment-0001.html>