linux-kernel - Re: [RFC PATCH 3/8] arm: parse cpu capacity from DT

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Message-ID: <20151211101232.GI14571@e106622-lin>
Date:	Fri, 11 Dec 2015 10:12:32 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Dietmar Eggemann <dietmar.eggemann@....com>
Cc:	linux-kernel@...r.kernel.org, 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
Subject: Re: [RFC PATCH 3/8] arm: parse cpu capacity from DT

Hi,

On 10/12/15 14:14, Dietmar Eggemann wrote:
> On 23/11/15 14:28, Juri Lelli wrote:
> > With the introduction of cpu capacity bindings, CPU capacities can now be
> > extracted from DT. Add parsing of such information at boot time. We keep
> > code that can produce same information, based on different DT properties
> > and hard-coded values, as fall-back for backward compatibility.
> 
> This patch-set should define _one_ way to be able to specify
> heterogeneous cpu capacity values for all arm and arm64 systems. So I
> would really like that we can agree on this solution ('capacity'
> property) and delete the old (cortex-a[15,7] only) solution based on
> struct cpu_efficiency table_efficiency[] and 'clock-frequency' property
> in arch/arm/kernel/topology.c. The appropriate code in
> arch/arm[,64]/kernel/topology.c should be the same. Everything else is
> highly confusing.
> 

Yeah, I tend to agree on this. I'd say that we could first agree on the
way we specify capacities and then we see what cleanups are required to
make things nicer.

Thanks,

- Juri

> > 
> > Cc: Russell King <linux@....linux.org.uk>
> > Signed-off-by: Juri Lelli <juri.lelli@....com>
> > ---
> >  arch/arm/kernel/topology.c | 50 +++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 49 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
> > index ec279d1..ecbff03 100644
> > --- a/arch/arm/kernel/topology.c
> > +++ b/arch/arm/kernel/topology.c
> > @@ -78,6 +78,35 @@ static unsigned long *__cpu_capacity;
> >  #define cpu_capacity(cpu)	__cpu_capacity[cpu]
> >  
> >  static unsigned long middle_capacity = 1;
> > +static bool capacity_from_dt = true;
> > +static u32 capacity_scale = SCHED_CAPACITY_SCALE;
> > +
> > +static int __init parse_cpu_capacity(struct device_node *cpu_node, int cpu)
> > +{
> > +	int ret = 1;
> > +	u32 cpu_capacity;
> > +
> > +	ret = of_property_read_u32(cpu_node,
> > +				   "capacity",
> > +				   &cpu_capacity);
> > +	if (!ret) {
> > +		u64 capacity;
> > +
> > +		/*
> > +		 * Enforce capacity <= capacity-scale.
> > +		 */
> > +		cpu_capacity = cpu_capacity <= capacity_scale ? cpu_capacity :
> > +			capacity_scale;
> > +		capacity = (cpu_capacity << SCHED_CAPACITY_SHIFT) /
> > +			capacity_scale;
> > +
> > +		set_capacity_scale(cpu, capacity);
> > +		pr_info("CPU%d: DT cpu capacity %lu\n",
> > +			cpu, arch_scale_cpu_capacity(NULL, cpu));
> > +	}
> > +
> > +	return !ret;
> > +}
> >  
> >  /*
> >   * Iterate all CPUs' descriptor in DT and compute the efficiency
> > @@ -99,6 +128,18 @@ static void __init parse_dt_topology(void)
> >  	__cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
> >  				 GFP_NOWAIT);
> >  
> > +	cn = of_find_node_by_path("/cpus");
> > +	if (!cn) {
> > +		pr_err("No CPU information found in DT\n");
> > +		return;
> > +	}
> > +
> > +	if (!of_property_read_u32(cn, "capacity-scale", &capacity_scale))
> > +		pr_info("DT cpus capacity-scale %u\n", capacity_scale);
> > +	else
> > +		pr_debug("DT cpus capacity-scale not found: assuming %u\n",
> > +			capacity_scale);
> > +
> >  	for_each_possible_cpu(cpu) {
> >  		const u32 *rate;
> >  		int len;
> > @@ -110,6 +151,13 @@ static void __init parse_dt_topology(void)
> >  			continue;
> >  		}
> >  
> > +		if (parse_cpu_capacity(cn, cpu)) {
> > +			of_node_put(cn);
> > +			continue;
> > +		}
> > +
> > +		capacity_from_dt = false;
> > +
> >  		for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++)
> >  			if (of_device_is_compatible(cn, cpu_eff->compatible))
> >  				break;
> > @@ -160,7 +208,7 @@ static void __init parse_dt_topology(void)
> >   */
> >  static void update_cpu_capacity(unsigned int cpu)
> >  {
> > -	if (!cpu_capacity(cpu))
> > +	if (!cpu_capacity(cpu) || capacity_from_dt)
> >  		return;
> >  
> >  	set_capacity_scale(cpu, cpu_capacity(cpu) / middle_capacity);
> > 
> 
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