[U-Boot] [PATCH] armv8: Enable CPUECTLR.SMPEN for data coherency

[Mark Rutland <mark.rutland@arm.com>]

On Thu, Jun 30, 2016 at 04:51:48PM +0800, Gong Qianyu wrote:
> From: Mingkai Hu <mingkai.hu@nxp.com>
> 
> Data coherency is enabled only when the CPUECTLR.SMPEN bit is
> set. The SMPEN bit should be set before enabling the data cache.
> If not enabled, the cache is not coherent with other cores and
> data corruption could occur.
> 
> Signed-off-by: Mingkai Hu <mingkai.hu@nxp.com>
> Signed-off-by: Gong Qianyu <Qianyu.Gong@nxp.com>
> 
> diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
> index 670e323..735dd67 100644
> --- a/arch/arm/cpu/armv8/start.S
> +++ b/arch/arm/cpu/armv8/start.S
> @@ -81,6 +81,11 @@ reset:
>  	msr	cpacr_el1, x0			/* Enable FP/SIMD */
>  0:
>  
> +	/* Enalbe SMPEN bit */
> +	mrs     x0, S3_1_c15_c2_1               /* cpuactlr_el1 */
> +	orr     x0, x0, #0x40
> +	msr     S3_1_c15_c2_1, x0

Please note that this register is IMPLEMENTATION DEFINED, and not
architectural, even though it happens to be common among ARM Ltd
implementations.

This is also not something that one can usually set on the Non-secure
side, and I'd expect Secure FW such as the ARM Trusted Firmware to
handle this.

If this is necessary within U-Boot, it should be guarded such that it
only runs on the relevant CPUs.

Thanks,
Mark.