[U-Boot] [PATCH v3 03/11] Exynos542x: Add workaround for ARM errata 798870

[Siarhei Siamashka <siarhei.siamashka@gmail.com>]

On Wed, 18 Feb 2015 15:16:27 +0530
Akshay Saraswat <akshay.s@samsung.com> wrote:

> This patch adds workaround for ARM errata 798870 which says
> "If back-to-back speculative cache line fills (fill A and fill B) are
> issued from the L1 data cache of a CPU to the L2 cache, the second
> request (fill B) is then cancelled, and the second request would have
> detected a hazard against a recent write or eviction (write B) to the
> same cache line as fill B then the L2 logic might deadlock."
> 
> Signed-off-by: Kimoon Kim <kimoon.kim@samsung.com>
> Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
> Reviewed-by: Simon Glass <sjg@chromium.org>
> Tested-by: Simon Glass <sjg@chromium.org>
> ---
> Changes since v2:
> 	- No change.
> 
> Changes since v1:
> 	- Added Reviewed-by & Tested-by.
> 	- Added space before */ on line # 40.
> 
>  arch/arm/cpu/armv7/exynos/lowlevel_init.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/arm/cpu/armv7/exynos/lowlevel_init.c b/arch/arm/cpu/armv7/exynos/lowlevel_init.c
> index e36f2fa..7335a1e 100644
> --- a/arch/arm/cpu/armv7/exynos/lowlevel_init.c
> +++ b/arch/arm/cpu/armv7/exynos/lowlevel_init.c
> @@ -46,6 +46,28 @@ enum {
>  
>  #ifdef CONFIG_EXYNOS5420
>  /*
> + * Set L2ACTLR[7] to reissue any memory transaction in the L2 that has been
> + * stalled for 1024 cycles to verify that its hazard condition still exists.
> + */

Having the ARM errata number mentioned in the comment here would make
the purpose of this code much more clear to anyone looking at it later
in the future.

Also isn't this a general purpose Cortex-A15 r2pX workaround,
also potentially useful for the other non-Exynos SoCs too?

> +void set_l2cache(void)
> +{
> +	uint32_t val;
> +
> +	/* Read MIDR for Primary Part Number */
> +	mrc_midr(val);
> +	val = (val >> 4);
> +	val &= 0xf;
> +
> +	/* L2ACTLR[7]: Enable hazard detect timeout for A15 */
> +	if (val == 0xf) {
> +		mrc_l2_aux_ctlr(val);
> +		val |= (1 << 7);
> +		mcr_l2_aux_ctlr(val);
> +		mrc_l2_ctlr(val);
> +	}
> +}
> +
> +/*
>   * Pointer to this function is stored in iRam which is used
>   * for jump and power down of a specific core.
>   */



-- 
Best regards,
Siarhei Siamashka