linux-kernel - Re: [PATCH v3 6/6] arm64: add sysfs cpu

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Date:	Fri, 5 Feb 2016 17:19:11 +0000
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org
Cc:	linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, peterz@...radead.org,
	vincent.guittot@...aro.org, robh+dt@...nel.org,
	mark.rutland@....com, linux@....linux.org.uk, sudeep.holla@....com,
	lorenzo.pieralisi@....com, catalin.marinas@....com,
	will.deacon@....com, morten.rasmussen@....com, broonie@...nel.org,
	Mark Brown <broonie@...aro.org>
Subject: Re: [PATCH v3 6/6] arm64: add sysfs cpu_capacity attribute

Hi Juri,

On 03/02/16 11:59, Juri Lelli wrote:
> Add a sysfs cpu_capacity attribute with which it is possible to read and
> write (thus over-writing default values) CPUs capacity. This might be
> useful in situation where there is no way to get proper default values
> at boot time.
> 
> The new attribute shows up as:
> 
>  /sys/devices/system/cpu/cpu*/cpu_capacity
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Mark Brown <broonie@...aro.org>
> Cc: Sudeep Holla <sudeep.holla@....com>
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> ---
>  arch/arm64/kernel/topology.c | 68 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index f2513a6..f05cc07 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -40,6 +40,74 @@ bool arch_wants_init_cpu_capacity(void)
>  	return true;
>  }
>  
> +#ifdef CONFIG_PROC_SYSCTL
> +#include <asm/cpu.h>
> +#include <linux/string.h>
> +static ssize_t show_cpu_capacity(struct device *dev,
> +				 struct device_attribute *attr,
> +				 char *buf)
> +{
> +	struct cpu *cpu = container_of(dev, struct cpu, dev);
> +	ssize_t rc;
> +	int cpunum = cpu->dev.id;
> +	unsigned long capacity = arch_scale_cpu_capacity(NULL, cpunum);

Gives me an implicit declaration of function ‘arch_scale_cpu_capacity’
error [without the commit fbc899610e1a ("arm64: Update
arch_scale_cpu_capacity() to reflect change to define") on your
git://linux-arm.org/linux-jl.git upstream/default_caps_v3 branch].

Why don't you just return cpu_scale

@@ -49,10 +49,8 @@ static ssize_t show_cpu_capacity(struct device *dev,
 {
        struct cpu *cpu = container_of(dev, struct cpu, dev);
        ssize_t rc;
-       int cpunum = cpu->dev.id;
-       unsigned long capacity = arch_scale_cpu_capacity(NULL, cpunum);

-       rc = sprintf(buf, "%lu\n", capacity);
+       rc = sprintf(buf, "%lu\n", per_cpu(cpu_scale, cpu->dev.id));

        return rc;
 }

to get rid of this dependency?

-- Dietmar

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