[PATCH] ARM: smp_scu: enable coherent speculative linefills

[Thomas Petazzoni]

Hello Russell,

Any chance to get this patch reviewed/applied? Should I simply submit
it to your patch tracking system?

Thanks,

Thomas

On Thu, 19 Mar 2015 14:54:15 +0100, Thomas Petazzoni wrote:
> According to the ARM TRM, about the SCU Control Register, bit 3
> (Speculative linefills enable) :
> 
>   When set, coherent linefill requests are sent speculatively to the
>   PL310 in parallel with the tag lookup. If the tag lookup misses, the
>   confirmed linefill is sent to the PL310 and gets Rdata earlier
>   because the data request was already initiated by the speculative
>   request. This feature works only if the PL310 is present in the
>   design.
> 
> This feature may improve the overall system performance.
> 
> Since the public ARM web site only documents Cortex-A9 revisions r2p0
> and later, we err on the safe side and only enable this bit on >= r2p0
> platforms, like the standby bit.
> 
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
> ---
>  arch/arm/kernel/smp_scu.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/kernel/smp_scu.c b/arch/arm/kernel/smp_scu.c
> index 72f9241..227bb86 100644
> --- a/arch/arm/kernel/smp_scu.c
> +++ b/arch/arm/kernel/smp_scu.c
> @@ -18,6 +18,7 @@
>  
>  #define SCU_CTRL		0x00
>  #define SCU_ENABLE		(1 << 0)
> +#define SCU_SPEC_LINEFILL	(1 << 3)
>  #define SCU_STANDBY_ENABLE	(1 << 5)
>  #define SCU_CONFIG		0x04
>  #define SCU_CPU_STATUS		0x08
> @@ -57,10 +58,13 @@ void scu_enable(void __iomem *scu_base)
>  
>  	scu_ctrl |= SCU_ENABLE;
>  
> -	/* Cortex-A9 earlier than r2p0 has no standby bit in SCU */
> +	/*
> +	 * Cortex-A9 earlier than r2p0 has no standby / speculative
> +	 * line fills bits in SCU
> +	 */
>  	if ((read_cpuid_id() & 0xff0ffff0) == 0x410fc090 &&
>  	    (read_cpuid_id() & 0x00f0000f) >= 0x00200000)
> -		scu_ctrl |= SCU_STANDBY_ENABLE;
> +		scu_ctrl |= SCU_STANDBY_ENABLE | SCU_SPEC_LINEFILL;
>  
>  	writel_relaxed(scu_ctrl, scu_base + SCU_CTRL);
>  



-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com