linux-kernel - Re: [PATCH v8 05/13] cpufreq: amd-pstate: optimize driver working mode selection in amd_pstate

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Date:   Mon, 19 Dec 2022 17:01:58 -0600
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Perry Yuan <perry.yuan@....com>, rafael.j.wysocki@...el.com,
        ray.huang@....com, viresh.kumar@...aro.org
Cc:     Deepak.Sharma@....com, Nathan.Fontenot@....com,
        Alexander.Deucher@....com, Shimmer.Huang@....com,
        Xiaojian.Du@....com, Li.Meng@....com, wyes.karny@....com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 05/13] cpufreq: amd-pstate: optimize driver working
 mode selection in amd_pstate_param()

On 12/19/2022 00:40, Perry Yuan wrote:
> There are some other amd pstate driver working mode to be supported.

Perhaps:

The amd-pstate driver may support multiple working modes. Introduce a 
variable to keep track of which mode is currently enabled.

> Here we use cppc_state var to indicate which mode is enabled.
> This change will help to simplify the the amd_pstate_param() to choose
> which mode used for the following driver registeration.

s/registeration/registration/

> 
> Signed-off-by: Perry Yuan <perry.yuan@....com>
> Signed-off-by: Wyes Karny <wyes.karny@....com>
> ---
>   drivers/cpufreq/amd-pstate.c | 35 +++++++++++++++++++++++++++--------
>   include/linux/amd-pstate.h   | 29 +++++++++++++++++++++++++++++
>   2 files changed, 56 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index c17bd845f5fc..861a905f9324 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -60,7 +60,18 @@
>    * module parameter to be able to enable it manually for debugging.
>    */
>   static struct cpufreq_driver amd_pstate_driver;
> -static int cppc_load __initdata;
> +static int cppc_state = AMD_PSTATE_DISABLE;
> +
> +static inline int get_mode_idx_from_str(const char *str, size_t size)
> +{
> +	int i;
> +
> +	for (i=0; i < AMD_PSTATE_MAX; i++) {
> +		if (!strncmp(str, amd_pstate_mode_string[i], size))
> +			return i;
> +	}
> +	return -EINVAL;
> +}
>   
>   static inline int pstate_enable(bool enable)
>   {
> @@ -628,7 +639,7 @@ static int __init amd_pstate_init(void)
>   	 * enable the amd_pstate passive mode driver explicitly
>   	 * with amd_pstate=passive in kernel command line
>   	 */
> -	if (!cppc_load) {
> +	if (cppc_state == AMD_PSTATE_DISABLE) {
>   		pr_debug("driver load is disabled, boot with amd_pstate=passive to enable this\n");

Presumably this message needs to be changed since there are different 
modes that can be used to enable it now.

>   		return -ENODEV;
>   	}
> @@ -671,16 +682,24 @@ device_initcall(amd_pstate_init);
>   
>   static int __init amd_pstate_param(char *str)
>   {
> +	size_t size;
> +	int mode_idx;
> +
>   	if (!str)
>   		return -EINVAL;
>   
> -	if (!strcmp(str, "disable")) {
> -		cppc_load = 0;
> -		pr_info("driver is explicitly disabled\n");
> -	} else if (!strcmp(str, "passive"))
> -		cppc_load = 1;
> +	size = strlen(str);
> +	mode_idx = get_mode_idx_from_str(str, size);
>   
> -	return 0;
> +	if (mode_idx >= AMD_PSTATE_DISABLE && mode_idx < AMD_PSTATE_MAX) {
> +		cppc_state = mode_idx;
> +		if (cppc_state == AMD_PSTATE_DISABLE)
> +			pr_info("driver is explicitly disabled\n");
> +
> +		return 0;
> +	}
> +
> +	return -EINVAL;
>   }
>   early_param("amd_pstate", amd_pstate_param);
>   
> diff --git a/include/linux/amd-pstate.h b/include/linux/amd-pstate.h
> index 1c4b8659f171..922d05a13902 100644
> --- a/include/linux/amd-pstate.h
> +++ b/include/linux/amd-pstate.h
> @@ -74,4 +74,33 @@ struct amd_cpudata {
>   	bool	boost_supported;
>   };
>   
> +/**
> + * enum amd_pstate_mode - driver working mode of amd pstate
> + */
> +
> +enum amd_pstate_mode {
> +	/** @AMD_PSTATE_DISABLE: Driver mode is disabled */
> +	AMD_PSTATE_DISABLE = 0,
> +
> +	/** @AMD_PSTATE_PASSIVE: Drier mode is passive mode */

s/Drier/Driver/

> +	AMD_PSTATE_PASSIVE = 1,
> +
> +	/** @AMD_PSTATE_ACTIVE: Driver mode is active mode */
> +	AMD_PSTATE_ACTIVE = 2,
> +
> +	/** @AMD_PSTATE_GUIDE: Driver mode is guided mode */
> +	AMD_PSTATE_GUIDE = 3,
> +
> +	/** @AMD_PSTATE_MAX */
> +	AMD_PSTATE_MAX = 4,
> +};
> +
> +static const char * const amd_pstate_mode_string[] = {
> +	[AMD_PSTATE_DISABLE]     = "disable",
> +	[AMD_PSTATE_PASSIVE]     = "passive",
> +	[AMD_PSTATE_ACTIVE]      = "active",
> +	[AMD_PSTATE_GUIDE]      = "guide",

I get the intent here, but guided mode isn't actually part of the v8
series under review.

I think it should either be folded into the series or this patch
should be split into two across the two patch-sets:
1) introduce the state machine (part of the EPP patch-set)
2) add guided mode support (part of the guided mode patch-set).

> +	NULL,
> +};
> +
>   #endif /* _LINUX_AMD_PSTATE_H */