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

Tom Rini
2015-03-12T13:41:00Z

On Wed, Mar 11, 2015 at 05:12:12PM -0300, 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]);

We should put this somewhere a bit more common that other A9 cores can
also call into like OMAP4, SoCFPGA and maybe zynq later (based on a
quick git grep pl310).

--
Tom
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