linux-kernel - Re: [PATCH 11/11] cpufreq: amd-pstate: automatically load pstate driver by default

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Date: Tue, 7 May 2024 09:41:29 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Perry Yuan <perry.yuan@....com>, rafael.j.wysocki@...el.com,
 viresh.kumar@...aro.org, Ray.Huang@....com, gautham.shenoy@....com,
 Borislav.Petkov@....com
Cc: Alexander.Deucher@....com, Xinmei.Huang@....com, Xiaojian.Du@....com,
 Li.Meng@....com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/11] cpufreq: amd-pstate: automatically load pstate
 driver by default

On 5/7/2024 02:15, Perry Yuan wrote:
> If the `amd-pstate` driver is not loaded automatically by default,
> it is because the kernel command line parameter has not been added.
> To resolve this issue, it is necessary to call the `amd_pstate_set_driver()`
> function to enable the desired mode (passive/active/guided) before registering
> the driver instance.
> This ensures that the driver is loaded correctly without relying on the kernel
> command line parameter.
> 
> [    0.917789] usb usb6: Manufacturer: Linux 6.9.0-rc6-amd-pstate-new-fix-v1 xhci-hcd
> [    0.982579] amd_pstate: failed to register with return -22
> 
> Reported-by: Andrei Amuraritei <andamu@...teo.net>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218705
> Signed-off-by: Perry Yuan <perry.yuan@....com>
> ---
>   drivers/cpufreq/amd-pstate.c | 39 +++++++++++++++++++-----------------
>   1 file changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 3ff381c4edf7..f5368497ee79 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -66,7 +66,7 @@
>   static struct cpufreq_driver *current_pstate_driver;
>   static struct cpufreq_driver amd_pstate_driver;
>   static struct cpufreq_driver amd_pstate_epp_driver;
> -static int cppc_state = AMD_PSTATE_UNDEFINED;
> +static int cppc_state;
>   static bool cppc_enabled;
>   static bool amd_pstate_prefcore = true;
>   static struct quirk_entry *quirks;
> @@ -1762,6 +1762,16 @@ static int __init amd_pstate_init(void)
>   	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
>   		return -ENODEV;
>   
> +	/* Disable on the following configs by default:
> +	 * 1. Undefined platforms
> +	 * 2. Server platforms
> +	 */
> +	if (amd_pstate_acpi_pm_profile_undefined() ||
> +		amd_pstate_acpi_pm_profile_server()) {
> +		pr_info("driver load is disabled for server or undefined platform\n");
> +		return -ENODEV;
> +	}
> +
>   	/* show debug message only if CPPC is not supported */
>   	if (!amd_cppc_supported())
>   		return -EOPNOTSUPP;
> @@ -1781,28 +1791,21 @@ static int __init amd_pstate_init(void)
>   	/* check if this machine need CPPC quirks */
>   	dmi_check_system(amd_pstate_quirks_table);
>   
> +	/* get default driver mode for loading*/
> +	cppc_state = CONFIG_X86_AMD_PSTATE_DEFAULT_MODE;

Rather than setting it here within amd_pstate_init() I think you can 
just set it at line 67 to CONFIG_X86_AMD_PSTATE_DEFAULT_MODE.

> +	pr_debug("cppc working state set to mode:%d\n", cppc_state);

I think this debug line is going to be unnecessary when it's already 
hardcoded to kernel config.

> +
>   	switch (cppc_state) {
> -	case AMD_PSTATE_UNDEFINED:
> -		/* Disable on the following configs by default:
> -		 * 1. Undefined platforms
> -		 * 2. Server platforms
> -		 * 3. Shared memory designs
> -		 */
> -		if (amd_pstate_acpi_pm_profile_undefined() ||
> -		    amd_pstate_acpi_pm_profile_server() ||
> -		    !cpu_feature_enabled(X86_FEATURE_CPPC)) {
> -			pr_info("driver load is disabled, boot with specific mode to enable this\n");
> -			return -ENODEV;
> -		}
> -		ret = amd_pstate_set_driver(CONFIG_X86_AMD_PSTATE_DEFAULT_MODE);
> -		if (ret)
> -			return ret;
> -		break;
>   	case AMD_PSTATE_DISABLE:
> +		pr_info("driver load is disabled, boot with specific mode to enable this\n");
>   		return -ENODEV;
> +	case AMD_PSTATE_UNDEFINED:

With the intent of this patch I no longer see a need for 
AMD_PSTATE_UNDEFINED in the rest of the driver (or in this case 
statement even).

I feel you can drop it from amd-pstate.h.

>   	case AMD_PSTATE_PASSIVE:
>   	case AMD_PSTATE_ACTIVE:
>   	case AMD_PSTATE_GUIDED:
> +		ret = amd_pstate_set_driver(cppc_state);
> +		if (ret)
> +			return ret;
>   		break;
>   	default:
>   		return -EINVAL;
> @@ -1823,7 +1826,7 @@ static int __init amd_pstate_init(void)
>   	/* enable amd pstate feature */
>   	ret = amd_pstate_enable(true);
>   	if (ret) {
> -		pr_err("failed to enable with return %d\n", ret);
> +		pr_err("failed to enable driver mode(%d) with return %d\n", cppc_state, ret);
>   		return ret;
>   	}
>