Re: [PATCH v2 2/3] cpufreq: amd-pstate: Allow replacing acpi-cpufreq when loaded

[Huang Rui <ray.huang@amd.com>]

On Tue, Mar 29, 2022 at 09:59:46AM +0800, Limonciello, Mario wrote:
> `amd-pstate` can be compiled as a module.  This however can be a
> deficiency because `acpi-cpufreq` will be loaded earlier when compiled
> into the kernel meaning `amd-pstate` doesn't get a chance.
> `acpi-cpufreq` is also unable to be unloaded in this circumstance.
> 
> To better improve the usability of `amd-pstate` when compiled as a module,
> add an optional module parameter that will force it to replace other
> cpufreq drivers at startup.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> v1->v2:
>  * Update to changes from v1.
>  * Verify the driver being matched is acpi-cpufreq.
>  * Show a message letting users know they can use amd-pstate.
> 
>  drivers/cpufreq/amd-pstate.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 7be38bc6a673..7dc2e344f222 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -63,6 +63,12 @@ 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 replace = false;
> +module_param(replace, bool, 0444);
> +MODULE_PARM_DESC(replace,
> +		  "replace acpi-cpufreq driver upon init if necessary");
> +extern void acpi_cpufreq_exit(void);
> +
>  static struct cpufreq_driver amd_pstate_driver;
>  
>  /**
> @@ -643,6 +649,7 @@ static struct cpufreq_driver amd_pstate_driver = {
>  
>  static int __init amd_pstate_init(void)
>  {
> +	const char *current_driver;
>  	int ret;
>  
>  	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
> @@ -653,9 +660,15 @@ static int __init amd_pstate_init(void)
>  		return -ENODEV;
>  	}
>  
> -	/* don't keep reloading if cpufreq_driver exists */
> -	if (cpufreq_get_current_driver())
> -		return -EEXIST;
> +	current_driver = cpufreq_get_current_driver();
> +	if (current_driver) {
> +		if (replace && strcmp(current_driver, "acpi-cpufreq") == 0) {

#ifdef CONFIG_X86_ACPI_CPUFREQ
> +			acpi_cpufreq_exit();
#endif

We need a kernel config checking here, otherwise, it will be built failed
once the acpi-cpufreq not set but amd_pstate is set.

Thanks,
Ray