Any input on this one?
Are there any other Armada XP users out there who could tell if they
also need such a workaround or if the current kernel works fine for them?
Sascha
On Thu, Aug 13, 2020 at 09:27:56AM +0200, Sascha Hauer wrote:
> It has been observed that some workloads (specifically iperf using
> a 2.5Gb network interface) die with an imprecise external abort when
> ECC is enabled in the L2 cache. It is assumed that the cache ECC
> functionality isn't directly at fault here, but just exposes another
> issue more openly by generating a slave error to what would otherwise
> be silent data corruption.
>
> The coherency protocol on Marvell Armada XP/375/38x requires that write
> misses allocate in the cache, so all requests should have the write-
> allocate attribute, which is done by setting the CPU pagetables to
> write-back write-allocate.
>
> Forcing all cacheable requests to allocate in the cache, by changing
> the allocation policy from "requester attribute" to "force allocate
> always", has been demonstrated to fix the issue in extensive testing.
> As this setting only enforces the requirements of the coherency
> protocol at the L2 cache level, instead of relying on requesters to
> provide the correct attribute, it is expected to have no adverse side
> effects and none have been found in the testing. Thus enabling this
> attribute override whenever the aurora cache is configured to be a
> coherent agent (no-outer) seem to be right thing to do.
>
> As we have no direct channel into Marvell to get more detailed
> information, as well as the Armada XP on which this behavior has been
> observed being a pretty old part by now, we can only speculate about
> the root cause. It may be a misguided CPU core optimization that tries
> to write-around the cache on specific access patterns, or it might be a
> bad interaction between the L2 cache and multiple concurrent masters.
>
> Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
> Signed-off-by: Lucas Stach, <l.stach at pengutronix.de>
> ---
> arch/arm/include/asm/hardware/cache-aurora-l2.h | 12 ++++++++++++
> arch/arm/mm/cache-l2x0.c | 12 +++++++++++-
> 2 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/hardware/cache-aurora-l2.h b/arch/arm/include/asm/hardware/cache-aurora-l2.h
> index 39769ffa00512..1a75b9b210a83 100644
> --- a/arch/arm/include/asm/hardware/cache-aurora-l2.h
> +++ b/arch/arm/include/asm/hardware/cache-aurora-l2.h
> @@ -31,6 +31,18 @@
> #define AURORA_ACR_REPLACEMENT_TYPE_SEMIPLRU \
> (3 << AURORA_ACR_REPLACEMENT_OFFSET)
>
> +#define AURORA_ACR_FORCE_WRITE_ALLOCATE_OFFSET 23
> +#define AURORA_ACR_FORCE_WRITE_ALLOCATE_MASK \
> + (0x3 << AURORA_ACR_FORCE_WRITE_ALLOCATE_OFFSET)
> +#define AURORA_ACR_FORCE_WRITE_ALLOCATE_REQUESTER \
> + (0 << AURORA_ACR_FORCE_WRITE_ALLOCATE_OFFSET)
> +#define AURORA_ACR_FORCE_WRITE_ALLOCATE_NEVER \
> + (1 << AURORA_ACR_FORCE_WRITE_ALLOCATE_OFFSET)
> +#define AURORA_ACR_FORCE_WRITE_ALLOCATE_ALWAYS \
> + (2 << AURORA_ACR_FORCE_WRITE_ALLOCATE_OFFSET)
> +#define AURORA_ACR_FORCE_WRITE_ALLOCATE_DT_ONLY \
> + (3 << AURORA_ACR_FORCE_WRITE_ALLOCATE_OFFSET)
> +
> #define AURORA_ACR_PARITY_EN (1 << 21)
> #define AURORA_ACR_ECC_EN (1 << 20)
>
> diff --git a/arch/arm/mm/cache-l2x0.c b/arch/arm/mm/cache-l2x0.c
> index 12c26eb88afbc..d0b03d77f3c5c 100644
> --- a/arch/arm/mm/cache-l2x0.c
> +++ b/arch/arm/mm/cache-l2x0.c
> @@ -1510,6 +1510,16 @@ static void __init aurora_of_parse(const struct device_node *np,
> *aux_mask &= ~mask;
> }
>
> +static void __init aurora_of_parse_no_outer(const struct device_node *np,
> + u32 *aux_val, u32 *aux_mask)
> +{
> + aurora_of_parse(np, aux_val, aux_mask);
> +
> + *aux_val &= ~AURORA_ACR_FORCE_WRITE_ALLOCATE_MASK;
> + *aux_val |= AURORA_ACR_FORCE_WRITE_ALLOCATE_ALWAYS;
> + *aux_mask &= ~AURORA_ACR_FORCE_WRITE_ALLOCATE_MASK;
> +}
> +
> static const struct l2c_init_data of_aurora_with_outer_data __initconst = {
> .type = "Aurora",
> .way_size_0 = SZ_4K,
> @@ -1535,7 +1545,7 @@ static const struct l2c_init_data of_aurora_no_outer_data __initconst = {
> .type = "Aurora",
> .way_size_0 = SZ_4K,
> .num_lock = 4,
> - .of_parse = aurora_of_parse,
> + .of_parse = aurora_of_parse_no_outer,
> .enable = aurora_enable_no_outer,
> .fixup = aurora_fixup,
> .save = aurora_save,
> --
> 2.28.0
>
>
--
Pengutronix e.K. | |
Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |