Re: [PATCH v9 09/13] cpufreq: amd-pstate: add driver working mode switch support

[Wyes Karny]

Hi Perry,

On 12/25/2022 10:04 PM, Perry Yuan wrote:
> From: Perry Yuan <Perry.Yuan@xxxxxxx>
> 
> 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@xxxxxxx>
> ---
>  drivers/cpufreq/amd-pstate.c | 118 +++++++++++++++++++++++++++++++++++
>  1 file changed, 118 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index e3676d1a85c7..8ceca4524fc1 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -63,6 +63,7 @@ static struct cpufreq_driver *default_pstate_driver;
>  static struct cpufreq_driver amd_pstate_driver;
>  static struct cpufreq_driver amd_pstate_epp_driver;
>  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)
>  {
> @@ -632,6 +633,8 @@ 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;
>  
> @@ -772,12 +775,99 @@ 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");

IMO 'disable' is more consistent to cppc_state.

> +
> +	return sysfs_emit(buf, "%s\n", amd_pstate_mode_string[cppc_state]);
> +}
> +
> +static void amd_pstate_driver_cleanup(void)
> +{
> +	default_pstate_driver = NULL;
> +}
> +
> +static int amd_pstate_update_status(const char *buf, size_t size)
> +{
> +	int ret;
> +	int mode_idx;
> +
> +	if (size > 7 || size < 3)
> +		return -EINVAL;
> +	mode_idx = get_mode_idx_from_str(buf, size);
> +
> +	switch(mode_idx) {
> +	case AMD_PSTATE_DISABLE:
> +		if (!default_pstate_driver)
> +			return -EINVAL;
> +		if (cppc_state == AMD_PSTATE_ACTIVE)
> +			return -EBUSY;
> +		ret = cpufreq_unregister_driver(default_pstate_driver);
> +		amd_pstate_driver_cleanup();
> +		break;
> +	case AMD_PSTATE_PASSIVE:
> +		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;
> +		}
> +
> +		ret = cpufreq_register_driver(default_pstate_driver);
> +		break;
> +	case AMD_PSTATE_ACTIVE:
> +		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;
> +		}
> +
> +		ret = cpufreq_register_driver(default_pstate_driver);
> +		break;
> +	default:
> +		break;
> +		ret = -EINVAL;
> +	}
> +
> +	return ret;
> +}

The implementation of amd_pstate_update_status function is good as long as the possible states are less.
Currently prev_state and next_state has 9 combinations. But with guided mode this becomes 16 combinations.
Do you have any concerns if I optimize this function by creating a state transition table in guided patch series?

> +
> +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,
> @@ -795,6 +885,15 @@ 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 int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>  {
>  	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
> @@ -1154,6 +1253,25 @@ 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:
> +	cpufreq_unregister_driver(default_pstate_driver);
>  	return ret;
>  }
>  device_initcall(amd_pstate_init);

-- 
Thanks & Regards,
Wyes