linux-kernel - Re: [PATCH v3 10/10] cpufreq: amd-pstate: automatically load pstate driver by default

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Message-ID: <87wmmti7b0.fsf@BLR-5CG11610CF.amd.com>
Date: Thu, 13 Jun 2024 13:49:15 +0530
From: Gautham R.Shenoy <gautham.shenoy@....com>
To: Perry Yuan <perry.yuan@....com>, <Mario.Limonciello@....com>
CC: <rafael.j.wysocki@...el.com>, <viresh.kumar@...aro.org>,
	<Ray.Huang@....com>, <Borislav.Petkov@....com>, <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 v3 10/10] cpufreq: amd-pstate: automatically load pstate
 driver by default

Hello Perry,


Perry Yuan <perry.yuan@....com> writes:

> 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.
>
> Meanwhle, user can add driver mode in command line which will override
> the kernel config default option.
>
> [    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 | 27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index fa486dfaa7e8..6e5c398810bf 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1841,28 +1841,37 @@ static int __init amd_pstate_init(void)
>  	/* check if this machine need CPPC quirks */
>  	dmi_check_system(amd_pstate_quirks_table);
>  
> -	switch (cppc_state) {
> -	case AMD_PSTATE_UNDEFINED:
> +	/*
> +	 * get driver mode for loading from command line choice or kernel config
> +	 * cppc_state will be AMD_PSTATE_UNDEFINED if no command line input
> +	 * command line choice will override the kconfig option
> +	 */
> +	if (cppc_state == AMD_PSTATE_UNDEFINED) {
> +		pr_err("pyuan cppc_state == AMD_PSTATE_UNDEFINED \n");

As Mario pointed out, this needs to be removed :-)

The following review comments are assuming that you want this patch so that
amd-pstate is the default driver on shared-memory non-server platforms.


>  		/* Disable on the following configs by default:
>  		 * 1. Undefined platforms
>  		 * 2. Server platforms
>  		 * 3. Shared memory designs

The comment says the driver needs to be disabled on the shared memory
designs by default. But...



>  		 */
>  		if (amd_pstate_acpi_pm_profile_undefined() ||
> -		    amd_pstate_acpi_pm_profile_server() ||
> -		    !cpu_feature_enabled(X86_FEATURE_CPPC)) {

...the check for shared-memory design has been removed. Is this
intentional ? So do you want the comment to be fixed so that it is clear
that we want amd-pstate to be the default driver on non-server platforms
?



> +		    amd_pstate_acpi_pm_profile_server()) {
>  			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;
> +		/* get driver mode from kernel config option [1:4] */
> +		cppc_state = CONFIG_X86_AMD_PSTATE_DEFAULT_MODE;

If someone booted the system with "amd_pstate=disable", the above will
overwrite that preference, no ?

> +	}
> +
> +	switch (cppc_state) {
>  	case AMD_PSTATE_DISABLE:
> +		pr_info("driver load is disabled, boot with specific mode to enable this\n");
>  		return -ENODEV;

....and this "case" statement will never be reachable in the
aforementioned case.


>  	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;
> @@ -1883,7 +1892,7 @@ 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)\n", cppc_state);
>  		return ret;
>  	}
>  
> -- 
> 2.34.1