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Date:   Mon, 19 Dec 2022 17:38:59 -0600
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Subject: Re: [PATCH v8 09/13] cpufreq: amd-pstate: add driver working mode
 switch support
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To:     Perry Yuan <perry.yuan@amd.com>, rafael.j.wysocki@intel.com,
        ray.huang@amd.com, viresh.kumar@linaro.org
Cc:     Deepak.Sharma@amd.com, Nathan.Fontenot@amd.com,
        Alexander.Deucher@amd.com, Shimmer.Huang@amd.com,
        Xiaojian.Du@amd.com, Li.Meng@amd.com, wyes.karny@amd.com,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20221219064042.661122-1-perry.yuan@amd.com>
 <20221219064042.661122-10-perry.yuan@amd.com>
From:   "Limonciello, Mario" <mario.limonciello@amd.com>
In-Reply-To: <20221219064042.661122-10-perry.yuan@amd.com>
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On 12/19/2022 00:40, Perry Yuan wrote:
> From: Perry Yuan <Perry.Yuan@amd.com>
> 
> While amd-pstate driver was loaded with specific driver mode, it will
> need to check which mode is enabled for the pstate driver,add this sysfs
> entry to show the current status
> 
> $ cat /sys/devices/system/cpu/amd-pstate/status
> active
> 
> Meanwhile, user can switch the pstate driver mode with writing mode
> string to sysfs entry as below.
> 
> Enable passive mode:
> $ sudo bash -c "echo passive >  /sys/devices/system/cpu/amd-pstate/status"
> 
> Enable active mode (EPP driver mode):
> $ sudo bash -c "echo active > /sys/devices/system/cpu/amd-pstate/status"
> 
> Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
> ---
>   drivers/cpufreq/amd-pstate.c | 128 +++++++++++++++++++++++++++++++++++
>   1 file changed, 128 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index fc12d35bc7bd..e8996e937e63 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -64,6 +64,7 @@ static struct cpufreq_driver amd_pstate_driver;
>   static struct cpufreq_driver amd_pstate_epp_driver;
>   static struct amd_cpudata **all_cpu_data;
>   static int cppc_state = AMD_PSTATE_DISABLE;
> +struct kobject *amd_pstate_kobj;
>   
>   static inline int get_mode_idx_from_str(const char *str, size_t size)
>   {
> @@ -90,6 +91,8 @@ static struct amd_pstate_params global_params;
>   static DEFINE_MUTEX(amd_pstate_limits_lock);
>   static DEFINE_MUTEX(amd_pstate_driver_lock);
>   
> +static DEFINE_SPINLOCK(cppc_notify_lock);
> +
>   static s16 amd_pstate_get_epp(struct amd_cpudata *cpudata, u64 cppc_req_cached)
>   {
>   	u64 epp;
> @@ -644,6 +647,8 @@ static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
>   	policy->driver_data = cpudata;
>   
>   	amd_pstate_boost_init(cpudata);
> +	if (!default_pstate_driver->adjust_perf)
> +		default_pstate_driver->adjust_perf = amd_pstate_adjust_perf;
>   
>   	return 0;
>   
> @@ -784,12 +789,106 @@ static ssize_t show_energy_performance_preference(
>   	return sysfs_emit(buf, "%s\n", energy_perf_strings[preference]);
>   }
>   
> +static ssize_t amd_pstate_show_status(char *buf)
> +{
> +	if (!default_pstate_driver)
> +		return sysfs_emit(buf, "off\n");
> +
> +	return sysfs_emit(buf, "%s\n", default_pstate_driver == &amd_pstate_epp_driver ?
> +					"active" : "passive");

Didn't you introduce const strings for this in an earlier patch from the 
series?

How about using the indices from that rather than hardcoding /another/ 
string.

Also keep in mind guided mode will be coming so
"case ? true_val : false_val"

So perhaps you should just have have some if cases so you don't have to 
switch the whole thing out.

> +}
> +
> +static void amd_pstate_driver_cleanup(void)
> +{
> +	unsigned int cpu;
> +
> +	cpus_read_lock();
> +	for_each_online_cpu(cpu) {
> +		if (all_cpu_data[cpu]) {
> +			spin_lock(&cppc_notify_lock);
> +			kfree(all_cpu_data[cpu]);
> +			WRITE_ONCE(all_cpu_data[cpu], NULL);
> +			spin_unlock(&cppc_notify_lock);
> +		}
> +	}
> +	cpus_read_unlock();
> +
> +	default_pstate_driver = NULL;
> +}
> +
> +static int amd_pstate_update_status(const char *buf, size_t size)
> +{

Rather than looking at each size for each case, how about you just look 
at the boundaries once?  Something like this:

if (size > 7 || size < 3)
	return -EINVAL;

Then you should be able to run strncmp for each of your cases.

> +	if (size == 3 && !strncmp(buf, "off", size)) {

This seems like another case that would be good to use the const strings 
you already introduced for state machine checking.

> +		if (!default_pstate_driver)
> +			return -EINVAL;
> +
> +		if (cppc_state == AMD_PSTATE_ACTIVE)
> +			return -EBUSY;
> +
> +		cpufreq_unregister_driver(default_pstate_driver);
> +		amd_pstate_driver_cleanup();
> +		return 0;
> +	}
> +
> +	if (size == 6 && !strncmp(buf, "active", size)) {

This seems like another case that would be good to use the const strings 
you already introduced for state machine checking.

> +		if (default_pstate_driver) {
> +			if (default_pstate_driver == &amd_pstate_epp_driver)
> +				return 0;
> +			cpufreq_unregister_driver(default_pstate_driver);
> +			default_pstate_driver = &amd_pstate_epp_driver;
> +			cppc_state = AMD_PSTATE_ACTIVE;
> +		}
> +
> +		return cpufreq_register_driver(default_pstate_driver);
> +	}
> +
> +	if (size == 7 && !strncmp(buf, "passive", size)) {

This seems like another case that would be good to use the const strings 
you already introduced for state machine checking.

> +		if (default_pstate_driver) {
> +			if (default_pstate_driver == &amd_pstate_driver)
> +				return 0;
> +			cpufreq_unregister_driver(default_pstate_driver);
> +			cppc_state = AMD_PSTATE_PASSIVE;
> +			default_pstate_driver = &amd_pstate_driver;
> +		}
> +
> +		return cpufreq_register_driver(default_pstate_driver);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static ssize_t show_status(struct kobject *kobj,
> +			   struct kobj_attribute *attr, char *buf)
> +{
> +	ssize_t ret;
> +
> +	mutex_lock(&amd_pstate_driver_lock);
> +	ret = amd_pstate_show_status(buf);
> +	mutex_unlock(&amd_pstate_driver_lock);
> +
> +	return ret;
> +}
> +
> +static ssize_t store_status(struct kobject *a, struct kobj_attribute *b,
> +			    const char *buf, size_t count)
> +{
> +	char *p = memchr(buf, '\n', count);
> +	int ret;
> +
> +	mutex_lock(&amd_pstate_driver_lock);
> +	ret = amd_pstate_update_status(buf, p ? p - buf : count);
> +	mutex_unlock(&amd_pstate_driver_lock);
> +
> +	return ret < 0 ? ret : count;
> +}
> +
>   cpufreq_freq_attr_ro(amd_pstate_max_freq);
>   cpufreq_freq_attr_ro(amd_pstate_lowest_nonlinear_freq);
>   
>   cpufreq_freq_attr_ro(amd_pstate_highest_perf);
>   cpufreq_freq_attr_rw(energy_performance_preference);
>   cpufreq_freq_attr_ro(energy_performance_available_preferences);
> +define_one_global_rw(status);
>   
>   static struct freq_attr *amd_pstate_attr[] = {
>   	&amd_pstate_max_freq,
> @@ -807,6 +906,15 @@ static struct freq_attr *amd_pstate_epp_attr[] = {
>   	NULL,
>   };
>   
> +static struct attribute *pstate_global_attributes[] = {
> +	&status.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group amd_pstate_global_attr_group = {
> +	.attrs = pstate_global_attributes,
> +};
> +
>   static inline void update_boost_state(void)
>   {
>   	u64 misc_en;
> @@ -1228,6 +1336,26 @@ static int __init amd_pstate_init(void)
>   	if (ret)
>   		pr_err("failed to register with return %d\n", ret);
>   
> +	amd_pstate_kobj = kobject_create_and_add("amd-pstate", &cpu_subsys.dev_root->kobj);
> +	if (!amd_pstate_kobj) {
> +		ret = -EINVAL;
> +		pr_err("global sysfs registration failed.\n");
> +		goto kobject_free;
> +	}
> +
> +	ret = sysfs_create_group(amd_pstate_kobj, &amd_pstate_global_attr_group);
> +	if (ret) {
> +		pr_err("sysfs attribute export failed with error %d.\n", ret);
> +		goto global_attr_free;
> +	}
> +
> +	return ret;
> +
> +global_attr_free:
> +	kobject_put(amd_pstate_kobj);
> +kobject_free:
> +	kfree(cpudata);
> +	cpufreq_unregister_driver(default_pstate_driver);
>   	return ret;
>   }
>   device_initcall(amd_pstate_init);