Subject: Re: [v5, PATCH 4/5] cpufreq: mediatek: add opp notification for SVS support

From: andrew-sh.cheng <[email-masked]>
Date: Mon, 9 Dec 2019 14:56:28 +0800

On Wed, 2019-11-27 at 14:06 +0530, Viresh Kumar wrote:
> On 26-11-19, 19:50, Andrew-sh.Cheng wrote:
> > diff --git a/drivers/cpufreq/mediatek-cpufreq.c b/drivers/cpufreq/mediatek-cpufreq.c
> > index 4b0cc50dd93b..7c37ab31230a 100644
> > --- a/drivers/cpufreq/mediatek-cpufreq.c
> > +++ b/drivers/cpufreq/mediatek-cpufreq.c
> > @@ -42,6 +42,10 @@ struct mtk_cpu_dvfs_info {
> >  	struct list_head list_head;
> >  	int intermediate_voltage;
> >  	bool need_voltage_tracking;
> > +	struct mutex lock; /* avoid notify and policy race condition */
> 
> Will a read-write lock be better suited here for performance reasons ?
Thank you for advice, I will check it.
> 
> > +	struct notifier_block opp_nb;
> > +	int opp_cpu;
> > +	unsigned long opp_freq;
> >  };
> >  
> >  static LIST_HEAD(dvfs_info_list);
> > @@ -231,6 +235,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
> >  	vproc = dev_pm_opp_get_voltage(opp);
> >  	dev_pm_opp_put(opp);
> >  
> > +	mutex_lock(&info->lock);
> >  	/*
> >  	 * If the new voltage or the intermediate voltage is higher than the
> >  	 * current voltage, scale up voltage first.
> > @@ -242,6 +247,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
> >  			pr_err("cpu%d: failed to scale up voltage!\n",
> >  			       policy->cpu);
> >  			mtk_cpufreq_set_voltage(info, old_vproc);
> > +			mutex_unlock(&info->lock);
> >  			return ret;
> >  		}
> >  	}
> > @@ -253,6 +259,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
> >  		       policy->cpu);
> >  		mtk_cpufreq_set_voltage(info, old_vproc);
> >  		WARN_ON(1);
> > +		mutex_unlock(&info->lock);
> >  		return ret;
> >  	}
> >  
> > @@ -263,6 +270,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
> >  		       policy->cpu);
> >  		clk_set_parent(cpu_clk, armpll);
> >  		mtk_cpufreq_set_voltage(info, old_vproc);
> > +		mutex_unlock(&info->lock);
> >  		return ret;
> >  	}
> >  
> > @@ -273,6 +281,7 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
> >  		       policy->cpu);
> >  		mtk_cpufreq_set_voltage(info, inter_vproc);
> >  		WARN_ON(1);
> > +		mutex_unlock(&info->lock);
> >  		return ret;
> >  	}
> >  
> > @@ -288,15 +297,75 @@ static int mtk_cpufreq_set_target(struct cpufreq_policy *policy,
> >  			clk_set_parent(cpu_clk, info->inter_clk);
> >  			clk_set_rate(armpll, old_freq_hz);
> >  			clk_set_parent(cpu_clk, armpll);
> > +			mutex_unlock(&info->lock);
> >  			return ret;
> >  		}
> >  	}
> >  
> > +	info->opp_freq = freq_hz;
> > +	mutex_unlock(&info->lock);
> > +
> >  	return 0;
> >  }
> >  
> >  #define DYNAMIC_POWER "dynamic-power-coefficient"
> >  
> > +static int mtk_cpufreq_opp_notifier(struct notifier_block *nb,
> > +				    unsigned long event, void *data)
> > +{
> > +	struct dev_pm_opp *opp = data;
> > +	struct dev_pm_opp *opp_item;
> > +	struct mtk_cpu_dvfs_info *info =
> > +		container_of(nb, struct mtk_cpu_dvfs_info, opp_nb);
> 
> Do the assignment after all definitions, instead of awkwardly breaking
> the line here.
Got it, will change it.
> 
> > +	unsigned long freq, volt;
> > +	struct cpufreq_policy *policy;
> > +	int ret = 0;
> > +
> > +	if (event == OPP_EVENT_ADJUST_VOLTAGE) {
> > +		freq = dev_pm_opp_get_freq(opp);
> > +
> > +		mutex_lock(&info->lock);
> > +		if (info->opp_freq == freq) {
> > +			volt = dev_pm_opp_get_voltage(opp);
> > +			ret = mtk_cpufreq_set_voltage(info, volt);
> > +			if (ret)
> > +				dev_err(info->cpu_dev, "failed to scale voltage: %d\n",
> > +					ret);
> > +		}
> > +		mutex_unlock(&info->lock);
> > +	} else if (event == OPP_EVENT_DISABLE) {
> > +		freq = info->opp_freq;
> > +		opp_item = dev_pm_opp_find_freq_ceil(info->cpu_dev, &freq);
> 
> name it new_opp instead of opp_item.
Got it, will change it.
> 
> > +		if (!IS_ERR(opp_item))
> > +			dev_pm_opp_put(opp_item);
> > +		else
> > +			freq = 0;
> > +
> 
> What is the purpose of the above code ?
When dev_pm_opp_find_freq_ceil() doesn't find matching opp item, freq
value won't be set.
Set it as 0 for below checking
> 
> > +		/* case of current opp is disabled */
> > +		if (freq == 0 || freq != info->opp_freq) {
> > +			// find an enable opp item
> 
> Use proper commenting style please.
Got it, will change it.
> 
> > +			freq = 1;
> > +			opp_item = dev_pm_opp_find_freq_ceil(info->cpu_dev,
> > +							     &freq);
> > +			if (!IS_ERR(opp_item)) {
> > +				dev_pm_opp_put(opp_item);
> > +				policy = cpufreq_cpu_get(info->opp_cpu);
> > +				if (policy) {
> > +					cpufreq_driver_target(policy,
> > +						freq / 1000,
> > +						CPUFREQ_RELATION_L);
> 
> Why don't you simply call this instead of all the code in the else
> block ?
These else code is used to check "current opp item is disabled or not".
If not, do nothing.
If current opp item is disabled, need to find an not-disabled opp item,
and set frequency to it.
> 
> > +					cpufreq_cpu_put(policy);
> > +				}
> > +			} else {
> > +				pr_err("%s: all opp items are disabled\n",
> > +				       __func__);
> > +			}
> > +		}
> > +	}
> > +
> > +	return notifier_from_errno(ret);
> > +}
> > +
> >  static int mtk_cpu_dvfs_info_init(struct mtk_cpu_dvfs_info *info, int cpu)
> >  {
> >  	struct device *cpu_dev;
> > @@ -383,11 +452,21 @@ static int mtk_cpu_dvfs_info_init(struct mtk_cpu_dvfs_info *info, int cpu)
> >  	info->intermediate_voltage = dev_pm_opp_get_voltage(opp);
> >  	dev_pm_opp_put(opp);
> >  
> > +	info->opp_cpu = cpu;
> > +	info->opp_nb.notifier_call = mtk_cpufreq_opp_notifier;
> > +	ret = dev_pm_opp_register_notifier(cpu_dev, &info->opp_nb);
> > +	if (ret) {
> > +		pr_warn("cannot register opp notification\n");
> > +		goto out_free_opp_table;
> > +	}
> > +
> > +	mutex_init(&info->lock);
> >  	info->cpu_dev = cpu_dev;
> >  	info->proc_reg = proc_reg;
> >  	info->sram_reg = IS_ERR(sram_reg) ? NULL : sram_reg;
> >  	info->cpu_clk = cpu_clk;
> >  	info->inter_clk = inter_clk;
> > +	info->opp_freq = clk_get_rate(cpu_clk);
> >  
> >  	/*
> >  	 * If SRAM regulator is present, software "voltage tracking" is needed
> > -- 
> > 2.12.5
> 

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