[U-Boot] [PATCH] mx6: Set shared override bit in PL310 AUX_CTRL register

[Stefano Babic <sbabic@denx.de>]

Hi Fabio,

On 11/03/2015 21:12, Fabio Estevam wrote:
> From: Fabio Estevam <fabio.estevam@freescale.com>
> 
> Having bit 22 cleared in the PL310 Auxiliary Control register (shared
> attribute override enable) has the side effect of transforming Normal
> Shared Non-cacheable reads into Cacheable no-allocate reads.
> 
> Coherent DMA buffers in Linux always have a Cacheable alias via the
> kernel linear mapping and the processor can speculatively load cache
> lines into the PL310 controller. With bit 22 cleared, Non-cacheable
> reads would unexpectedly hit such cache lines leading to buffer
> corruption.
> 
> This was inspired by a patch from Catalin Marinas [1] and also from recent 
> discussions in the linux-arm-kernel list [2] where Russell King and Rob Herring 
> suggested that bootloaders should initialize the cache. 
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2010-November/031810.html
> [2] https://lkml.org/lkml/2015/2/20/199
> 
> Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
> ---
>  arch/arm/cpu/armv7/mx6/soc.c | 8 ++++++++
>  arch/arm/include/asm/pl310.h | 2 ++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/arch/arm/cpu/armv7/mx6/soc.c b/arch/arm/cpu/armv7/mx6/soc.c
> index ef02972..5aab305 100644
> --- a/arch/arm/cpu/armv7/mx6/soc.c
> +++ b/arch/arm/cpu/armv7/mx6/soc.c
> @@ -506,6 +506,14 @@ void v7_outer_cache_enable(void)
>  	struct pl310_regs *const pl310 = (struct pl310_regs *)L2_PL310_BASE;
>  	unsigned int val;
>  
> +
> +	/*
> +	 * Set bit 22 in the auxiliary control register. If this bit
> +	 * is cleared, PL310 treats Normal Shared Non-cacheable
> +	 * accesses as Cacheable no-allocate.
> +	 */
> +	setbits_le32(&pl310->pl310_aux_ctrl, L310_SHARED_ATT_OVERRIDE_ENABLE);
> +
>  #if defined CONFIG_MX6SL
>  	struct iomuxc *iomux = (struct iomuxc *)IOMUXC_BASE_ADDR;
>  	val = readl(&iomux->gpr[11]);
> diff --git a/arch/arm/include/asm/pl310.h b/arch/arm/include/asm/pl310.h
> index ddc245b..de7650e 100644
> --- a/arch/arm/include/asm/pl310.h
> +++ b/arch/arm/include/asm/pl310.h
> @@ -16,6 +16,8 @@
>  #define L2X0_STNDBY_MODE_EN			(1 << 0)
>  #define L2X0_CTRL_EN				1
>  
> +#define L310_SHARED_ATT_OVERRIDE_ENABLE		(1 << 22)
> +
>  struct pl310_regs {
>  	u32 pl310_cache_id;
>  	u32 pl310_cache_type;
> 

It looks like from the discussion and the following threads that a
general solution cannot be easy found. I agree with you to apply it at
least for i.MX6, and let's see if in the future we can factorize it for
other SOCs.

Best regards,
Stefano Babic

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