linux-kernel - Re: [PATCH] MIPS: Flush cache after DMA_FROM_DEVICE for agressively speculative CPUs

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Date:	Wed, 13 May 2015 19:49:11 -0700
From:	Kevin Cernekee <cernekee@...il.com>
To:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
Cc:	mina86@...a86.com,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	Zubair.Kakakhel@...tec.com, Ralf Baechle <ralf@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH] MIPS: Flush cache after DMA_FROM_DEVICE for agressively
 speculative CPUs

On Wed, May 13, 2015 at 6:49 PM, Leonid Yegoshin
<Leonid.Yegoshin@...tec.com> wrote:
> Some MIPS CPUs have an aggressive speculative load and may erroneuosly load
> some cache line in the middle of DMA transaction. CPU discards result but cache
> doesn't. If DMA happens from device then additional cache invalidation is needed
> on that CPU's after DMA.
>
> Found in test.
>
> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
> ---
>  arch/mips/mm/dma-default.c |   10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
> index 609d1241b0c4..ccf49ecfbf8c 100644
> --- a/arch/mips/mm/dma-default.c
> +++ b/arch/mips/mm/dma-default.c
> @@ -67,11 +67,13 @@ static inline struct page *dma_addr_to_page(struct device *dev,
>   * systems and only the R10000 and R12000 are used in such systems, the
>   * SGI IP28 Indigo² rsp. SGI IP32 aka O2.
>   */
> -static inline int cpu_needs_post_dma_flush(struct device *dev)
> +static inline int cpu_needs_post_dma_flush(struct device *dev,
> +                                          enum dma_data_direction direction)
>  {
>         return !plat_device_is_coherent(dev) &&
>                (boot_cpu_type() == CPU_R10000 ||
>                 boot_cpu_type() == CPU_R12000 ||
> +               (cpu_has_maar && (direction != DMA_TO_DEVICE)) ||
>                 boot_cpu_type() == CPU_BMIPS5000);

Can all of these CPUs safely skip the post_dma_flush on DMA_TO_DEVICE
(not just maar)?
--
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