Re: [PATCH v2 5/6] cpufreq: amd_pstate: Add guided mode control support via sysfs

[Mario Limonciello <mario.limonciello@amd.com>]

On 1/12/23 23:21, Wyes Karny wrote:
> amd_pstate driver's `status` sysfs entry helps to control the driver's
> mode dynamically by user. After the addition of guided mode the
> combinations of mode transitions have been increased (16 combinations).
> Therefore optimise the amd_pstate_update_status function by implementing
> a state transition table.
> 
> There are 4 states amd_pstate supports, namely: 'disable', 'passive',
> 'active', and 'guided'.  The transition from any state to any other
> state is possible after this change. Only if the state requested matches
> with the current state then -EBUSY value is returned.
> 
> Sysfs interface:
> 
> To disable amd_pstate driver:
>   # echo disable > /sys/devices/system/cpu/amd_pstate/status
> 
> To enable passive mode:
>   # echo passive > /sys/devices/system/cpu/amd_pstate/status
> 
> To change mode to active:
>   # echo active > /sys/devices/system/cpu/amd_pstate/status
> 
> To change mode to guided:
>   # echo guided > /sys/devices/system/cpu/amd_pstate/status
> 
> Signed-off-by: Wyes Karny <wyes.karny@amd.com>
> ---
>   drivers/cpufreq/amd-pstate.c | 144 ++++++++++++++++++++++++++---------
>   1 file changed, 109 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 20d78dad712d..4a2b559fd712 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -65,6 +65,8 @@ static struct cpufreq_driver amd_pstate_epp_driver;
>   static int cppc_state = AMD_PSTATE_DISABLE;
>   struct kobject *amd_pstate_kobj;
>   
> +typedef int (*cppc_mode_transition_fn)(int);
> +
>   static inline int get_mode_idx_from_str(const char *str, size_t size)
>   {
>   	int i;
> @@ -806,55 +808,127 @@ static ssize_t amd_pstate_show_status(char *buf)
>   
>   static void amd_pstate_driver_cleanup(void)
>   {
> +	amd_pstate_enable(false);
> +	cppc_state = AMD_PSTATE_DISABLE;
>   	default_pstate_driver = NULL;
>   }
>   
> -static int amd_pstate_update_status(const char *buf, size_t size)
> +static int amd_pstate_register_driver(int mode)
>   {
>   	int ret;
> -	int mode_idx;
>   
> -	if (size > 7 || size < 3)
> +	if (mode == AMD_PSTATE_PASSIVE || mode == AMD_PSTATE_GUIDED)
> +		default_pstate_driver = &amd_pstate_driver;
> +	else if (mode == AMD_PSTATE_ACTIVE)
> +		default_pstate_driver = &amd_pstate_epp_driver;
> +	else
>   		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);
> +	ret = cpufreq_register_driver(default_pstate_driver);
> +	if (ret) {
>   		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;
> -		}
> +		return ret;
> +	}
>   
> -		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;
> +	cppc_state = mode;
> +	return 0;
> +}
> +
> +static int amd_pstate_unregister_driver(int dummy)
> +{
> +	int ret;
> +
> +	ret = cpufreq_unregister_driver(default_pstate_driver);
> +
> +	if (ret)
> +		return ret;
> +
> +	amd_pstate_driver_cleanup();
> +	return 0;
> +}
> +
> +static void amd_pstate_change_mode_without_dvr_change(int mode)
> +{
> +	int cpu = 0;
> +
> +	cppc_state = mode;
> +	if (!boot_cpu_has(X86_FEATURE_CPPC)) {

You can save some indentation by inverting the check and calling "return".

> +		if (cppc_state == AMD_PSTATE_PASSIVE) {
> +			for_each_present_cpu(cpu) {
> +				cppc_set_auto_sel(cpu, 0);
> +			}
> +		} else if (cppc_state == AMD_PSTATE_GUIDED) {
> +				for_each_present_cpu(cpu) {
> +					cppc_set_auto_sel(cpu, 1);
> +				}
>   		}
> +	}
> +}
>   
> -		ret = cpufreq_register_driver(default_pstate_driver);
> -		break;
> -	default:
> -		break;
> -		ret = -EINVAL;
> +static int amd_pstate_change_driver_mode(int mode)
> +{
> +	int ret;
> +
> +	if ((mode == AMD_PSTATE_GUIDED && cppc_state == AMD_PSTATE_PASSIVE) ||
> +			(mode == AMD_PSTATE_PASSIVE && cppc_state == AMD_PSTATE_GUIDED)) {
> +		amd_pstate_change_mode_without_dvr_change(mode);
> +		return 0;

This feels like you're duplicating your logic of your mode transition 
table.  How about having the mode transition table call the function for 
changing modes without a driver change directly instead for those cases?

>   	}
>   
> -	return ret;
> +	ret = amd_pstate_unregister_driver(0);
> +	if (ret)
> +		return ret;
> +
> +	ret = amd_pstate_register_driver(mode);
> +	if (ret)
> +		return ret;
> +
> +	return 0;
> +}
> +
> +/* Mode transition table */
> +cppc_mode_transition_fn mode_state_machine[AMD_PSTATE_MAX][AMD_PSTATE_MAX] = {
> +	[AMD_PSTATE_DISABLE]         = {
> +		[AMD_PSTATE_DISABLE]     = NULL,
> +		[AMD_PSTATE_PASSIVE]     = amd_pstate_register_driver,
> +		[AMD_PSTATE_ACTIVE]      = amd_pstate_register_driver,
> +		[AMD_PSTATE_GUIDED]      = amd_pstate_register_driver,
> +	},
> +	[AMD_PSTATE_PASSIVE]         = {
> +		[AMD_PSTATE_DISABLE]     = amd_pstate_unregister_driver,
> +		[AMD_PSTATE_PASSIVE]     = NULL,
> +		[AMD_PSTATE_ACTIVE]      = amd_pstate_change_driver_mode,
> +		[AMD_PSTATE_GUIDED]      = amd_pstate_change_driver_mode,
> +	},
> +	[AMD_PSTATE_ACTIVE]          = {
> +		[AMD_PSTATE_DISABLE]     = amd_pstate_unregister_driver,
> +		[AMD_PSTATE_PASSIVE]     = amd_pstate_change_driver_mode,
> +		[AMD_PSTATE_ACTIVE]      = NULL,
> +		[AMD_PSTATE_GUIDED]      = amd_pstate_change_driver_mode,
> +	},
> +	[AMD_PSTATE_GUIDED]          = {
> +		[AMD_PSTATE_DISABLE]     = amd_pstate_unregister_driver,
> +		[AMD_PSTATE_PASSIVE]     = amd_pstate_change_driver_mode,
> +		[AMD_PSTATE_ACTIVE]      = amd_pstate_change_driver_mode,
> +		[AMD_PSTATE_GUIDED]      = NULL,
> +	},
> +};
> +
> +static int amd_pstate_update_status(const char *buf, size_t size)
> +{
> +	int mode_idx;
> +
> +	if (size > 7 || size < 3)
> +		return -EINVAL;

The compiler typically inlines strlen.  Perhaps to make this more 
obvious what these boundaries are maybe do this:

size > strlen("passive") || size < strlen("off")

> +	mode_idx = get_mode_idx_from_str(buf, size);
> +
> +	if (mode_idx < 0 || mode_idx >= AMD_PSTATE_MAX)
> +		return -EINVAL;
> +
> +	if (mode_state_machine[cppc_state][mode_idx])
> +		return mode_state_machine[cppc_state][mode_idx](mode_idx);
> +
> +	return -EBUSY;
>   }
>   
>   static ssize_t show_status(struct kobject *kobj,