[PATCH 1/2 v2] ARM: l2x0: make it possible to disable outer sync from DT

Rob Herring robh at kernel.org
Sat Dec 19 19:39:24 PST 2015

On Mon, Dec 14, 2015 at 09:53:05PM +0100, Linus Walleij wrote:
> According to commit 2503a5ecd86c002506001eba432c524ea009fe7f
> "ARM: 6201/1: RealView: Do not use outer_sync() on ARM11MPCore
> boards with L220" Some PB11MPCore RealView core tiles have broken
> outer_sync.
> We got rid of the custom barriers from the machine by disabling
> outer sync, but that was just for the boardfile case. We have
> to be able to do the same in the device tree case.
> Since __l2c_init() is cloning and copying the L2C vtable,
> we pass an argument to this function to optionally numb
> the outer sync operation if desired, before initializing
> the cache.
> After this we can set up the cache correctly on the RealView
> PB11MPCore. This was tested on a PB11MPCore known to have the
> issue. Before this, spurious crashes would occur if we try to
> set up the cache properly, after this it boots rock solid.
> Cc: Russell King <linux at arm.linux.org.uk>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: devicetree at vger.kernel.org
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
> ---
> ChangeLog v2->v3:
> - Update description, reference Catalins initial commit in the
>   commit blurb.
> ---
>  Documentation/devicetree/bindings/arm/l2cc.txt |  3 +++
>  arch/arm/mm/cache-l2x0.c                       | 13 ++++++++++---
>  2 files changed, 13 insertions(+), 3 deletions(-)
> diff --git a/Documentation/devicetree/bindings/arm/l2cc.txt b/Documentation/devicetree/bindings/arm/l2cc.txt
> index d181b7c4c522..416864e9dc92 100644
> --- a/Documentation/devicetree/bindings/arm/l2cc.txt
> +++ b/Documentation/devicetree/bindings/arm/l2cc.txt
> @@ -75,6 +75,9 @@ Optional properties:
>    specified to indicate that such transforms are precluded.
>  - arm,parity-enable : enable parity checking on the L2 cache (L220 or PL310).
>  - arm,parity-disable : disable parity checking on the L2 cache (L220 or PL310).
> +- arm,outer-sync-disable : disable the outer sync operation on the L2 cache.
> +  Some core tiles, especially ARM PB11MPCore have a faulty L220 cache that
> +  will randomly hang unless outer sync operations are disabled.

This is also useful on Highbank as a feature where all DMA goes thru the 
ACP port and there should not be a need to flush the L2 write buffer. 
But I already optimized the performance critical register accesses with 
_relaxed variants, so it doesn't really matter. I don't think any other 
platform cares, therefore:

Acked-by: Rob Herring <robh at kernel.org>


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