linux-kernel - Re: [PATCH v4 6/6] cpufreq: CPPC: Support for autonomous selection in cppc

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Message-ID: <Z4fLXPgMvwGur+pz@BLRRASHENOY1.amd.com>
Date: Wed, 15 Jan 2025 20:21:08 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Lifeng Zheng <zhenglifeng1@...wei.com>
Cc: rafael@...nel.org, lenb@...nel.org, robert.moore@...el.com,
	viresh.kumar@...aro.org, mario.limonciello@....com,
	ray.huang@....com, pierre.gondois@....com,
	acpica-devel@...ts.linux.dev, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linuxarm@...wei.com, jonathan.cameron@...wei.com,
	zhanjie9@...ilicon.com, lihuisong@...wei.com, hepeng68@...wei.com,
	fanghao11@...wei.com
Subject: Re: [PATCH v4 6/6] cpufreq: CPPC: Support for autonomous selection
 in cppc_cpufreq

Hello Lifeng,


On Mon, Jan 13, 2025 at 08:21:04PM +0800, Lifeng Zheng wrote:
> Add sysfs interfaces for CPPC autonomous selection in the cppc_cpufreq
> driver.
> 

[..snip..]

> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index bd8f75accfa0..ea6c6a5bbd8c 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -814,10 +814,119 @@ static ssize_t show_freqdomain_cpus(struct cpufreq_policy *policy, char *buf)
>  
>  	return cpufreq_show_cpus(cpu_data->shared_cpu_map, buf);
>  }
> +
> +static ssize_t show_auto_select(struct cpufreq_policy *policy, char *buf)
> +{
> +	bool val;
> +	int ret;
> +
> +	ret = cppc_get_auto_sel(policy->cpu, &val);
> +
> +	/* show "<unsupported>" when this register is not supported by cpc */
> +	if (ret == -EOPNOTSUPP)
> +		return sysfs_emit(buf, "%s\n", "<unsupported>");
> +
> +	if (ret)
> +		return ret;
> +
> +	return sysfs_emit(buf, "%d\n", val);
> +}
> +
> +static ssize_t store_auto_select(struct cpufreq_policy *policy,
> +				 const char *buf, size_t count)
> +{
> +	bool val;
> +	int ret;
> +
> +	ret = kstrtobool(buf, &val);
> +	if (ret)
> +		return ret;
> +
> +	ret = cppc_set_auto_sel(policy->cpu, val);

When the auto_select register is not supported, since
cppc_set_reg_val() doesn't have the !CPC_SUPPORTED(reg) check, that
function won't return an error, and thus this store function won't
return an error either. Should there be a !CPC_SUPPORTED(reg) check in
cppc_set_reg_val() as well? Or should the store function call
cppc_get_auto_sel() to figure out if the register is supported or not?

--
Thanks and Regards
gautham.