[PATCH 2/2] ARM: cache: assume 64-byte L1 cachelines for ARMv7 CPUs

[Will Deacon]

On Mon, Jan 16, 2012 at 04:09:31PM +0000, Russell King - ARM Linux wrote:
> On Mon, Jan 16, 2012 at 04:52:14PM +0100, Shilimkar, Santosh wrote:
> > Will,
> > On Mon, Jan 16, 2012 at 4:44 PM, Will Deacon <will.deacon at arm.com> wrote:
> > > To ensure correct alignment of cacheline-aligned data, the maximum
> > > cacheline size needs to be known at compile time.
> > >
> > > Since Cortex-A8 and Cortex-A15 have 64-byte cachelines (and it is likely
> > > that there will be future ARMv7 implementations with the same line size)
> > > then it makes sense to assume that CPU_V7 implies a 64-byte L1 cacheline
> > > size. For CPUs with smaller caches, this will result in some harmless
> > > padding but will help with single zImage work and avoid hitting subtle
> > > bugs with misaligned data structures.
> > >
> > > Signed-off-by: Will Deacon <will.deacon at arm.com>
> > > ---
> > >  arch/arm/mm/Kconfig |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> > > index 4cefb57..493e5ea5 100644
> > > --- a/arch/arm/mm/Kconfig
> > > +++ b/arch/arm/mm/Kconfig
> > > @@ -887,7 +887,7 @@ config ARM_L1_CACHE_SHIFT_6
> > >
> > >  config ARM_L1_CACHE_SHIFT
> > >        int
> > > -       default 6 if ARM_L1_CACHE_SHIFT_6
> > > +       default 6 if ARM_L1_CACHE_SHIFT_6 || CPU_V7
> > 
> > Will be really harmless on A9 ? We have L2 also to be
> > considered here which hard codes the line size as 32.
> 
> Going for a larger cache line size is safe: this is used for aligning
> data structures and similar, and aligning to 64-byte means that it's
> also 32-byte aligned.

Indeed, it should be fine. As for L2, that's something that should only
affect the L2CC code so we don't need a compile-time definition for that.

I might rework this code anyway (this was just to see what people think of
the idea) so that ARM_L1_CACHE_SHIFT_6 is selected by CPU_V7. Then I can
remove the explicit selects of the config option by platforms that already
select CPU_V7.

Will