linux-kernel - Re: [PATCH v4 3/9] cpufreq: amd-pstate: change amd-pstate driver to be built-in type

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Date:   Mon, 14 Nov 2022 16:46:03 -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 v4 3/9] cpufreq: amd-pstate: change amd-pstate driver to
 be built-in type

On 11/10/2022 11:58, Perry Yuan wrote:
> Change the `amd-pstate` driver as the built-in type which can help to
> load the driver before the acpi_cpufreq driver as the default pstate
> driver for the AMD processors.
> 
> for the processors do not have the dedicated MSR functions, add
> `amd-pstate=legacy_cppc` to grub which enable shared memory interface
> to communicate with cppc_acpi module to control pstate hints.

Did you sync with Wyes already as I had suggested?  Was this the outcome?

I was a bit surprised to see this still as legacy_cppc when reviewing v4.

> 
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>   drivers/cpufreq/Kconfig.x86  |  2 +-
>   drivers/cpufreq/amd-pstate.c | 25 +++++++++++++++----------
>   2 files changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> index 310779b07daf..00476e94db90 100644
> --- a/drivers/cpufreq/Kconfig.x86
> +++ b/drivers/cpufreq/Kconfig.x86
> @@ -35,7 +35,7 @@ config X86_PCC_CPUFREQ
>   	  If in doubt, say N.
>   
>   config X86_AMD_PSTATE
> -	tristate "AMD Processor P-State driver"
> +	bool "AMD Processor P-State driver"
>   	depends on X86 && ACPI
>   	select ACPI_PROCESSOR
>   	select ACPI_CPPC_LIB if X86_64
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index ace7d50cf2ac..85a0b3fb56c2 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -59,10 +59,7 @@
>    * we disable it by default to go acpi-cpufreq on these processors and add a
>    * module parameter to be able to enable it manually for debugging.
>    */
> -static bool shared_mem = false;
> -module_param(shared_mem, bool, 0444);
> -MODULE_PARM_DESC(shared_mem,
> -		 "enable amd-pstate on processors with shared memory solution (false = disabled (default), true = enabled)");
> +static bool shared_mem __read_mostly;
>   
>   static struct cpufreq_driver amd_pstate_driver;
>   
> @@ -653,16 +650,24 @@ static int __init amd_pstate_init(void)
>   
>   	return ret;
>   }
> +device_initcall(amd_pstate_init);
>   
> -static void __exit amd_pstate_exit(void)
> +static int __init amd_pstate_param(char *str)
>   {
> -	cpufreq_unregister_driver(&amd_pstate_driver);
> +	if (!str)
> +		return -EINVAL;
>   
> -	amd_pstate_enable(false);
> -}
> +	/*
> +	 * support shared memory type CPPC which has no MSR function.
> +	 * enable amd-pstate on processors with shared memory solution
> +	 * (amd-pstate=legacy_cppc enabled), it is disabled by default.
> +	 */
> +	if (!strcmp(str, "legacy_cppc"))
> +		shared_mem = true;
>   
> -module_init(amd_pstate_init);
> -module_exit(amd_pstate_exit);
> +	return 0;
> +}
> +early_param("amd-pstate", amd_pstate_param);

Documentation/kernel-parameters.txt needs to be updated for this early 
parameter support.

>   
>   MODULE_AUTHOR("Huang Rui <ray.huang@....com>");
>   MODULE_DESCRIPTION("AMD Processor P-state Frequency Driver");