Re: [PATCH] ARM: mm: add ARM_L1_CACHE_SHIFT_7 for UniPhier outer cache

[Masahiro Yamada]

Hi.

If there is no objection to this patch,
I will put it into Russell's patch tracker.


2016-10-19 21:39 GMT+09:00 Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>:
> The UniPhier outer cache (arch/arm/mm/cache-uniphier.c) has 128 byte
> line length and its tags are also managed per 128 byte line.  This
> is very unfortunate, but the current 64 byte alignment for kmalloc()
> causes sharing problems on DMA if used with this outer cache.
>
> This commit adds ARM_L1_CACHE_SHIFT_7 to increase the DMA minimum
> alignment to 128 byte if CACHE_UNIPHIER is enabled.  There are
> several drivers that assume aligning to L1_CACHE_BYTES will be DMA
> safe, so this commit also changes the L1_CACHE_BYTES for safety.
>
> Having said that, I hesitate to align all the other SoCs in Multi
> platform to the UniPhier's requirement.  So, I am disabling the
> CONFIG_CACHE_UNIPHIER by default, so that multi_v7_defconfig will
> still with CONFIG_ARM_L1_CACHE_SHIFT=6.  With this, UniPhier SoCs
> become a bit slower, but it is much better than system crash.
> If desired, the outer-cache can be enabled by the merge_config or
> something.
>
> Note:
> The UniPhier PH1-Pro5 SoC is equipped also with L3 cache with 256 byte
> line size but its tags are managed per 128 byte sub-line.
> So, ARM_L1_CACHE_SHIFT_7 should be fine for all the UniPhier SoCs.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> ---
>
> I threw a question in January this year:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/400289.html
>
> After a long interval, I came back to this topic.
>
>
>  arch/arm/mm/Kconfig | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
> index c1799dd..f68e8ec 100644
> --- a/arch/arm/mm/Kconfig
> +++ b/arch/arm/mm/Kconfig
> @@ -991,7 +991,7 @@ config CACHE_TAUROS2
>  config CACHE_UNIPHIER
>         bool "Enable the UniPhier outer cache controller"
>         depends on ARCH_UNIPHIER
> -       default y
> +       select ARM_L1_CACHE_SHIFT_7
>         select OUTER_CACHE
>         select OUTER_CACHE_SYNC
>         help
> @@ -1012,8 +1012,14 @@ config ARM_L1_CACHE_SHIFT_6
>         help
>           Setting ARM L1 cache line size to 64 Bytes.
>
> +config ARM_L1_CACHE_SHIFT_7
> +       bool
> +       help
> +         Setting ARM L1 cache line size to 128 Bytes.
> +
>  config ARM_L1_CACHE_SHIFT
>         int
> +       default 7 if ARM_L1_CACHE_SHIFT_7
>         default 6 if ARM_L1_CACHE_SHIFT_6
>         default 5
>
> --
> 1.9.1
>
>
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-- 
Best Regards
Masahiro Yamada