Re: [PATCH v3 06/12] amd-pstate: Add sysfs support for floor_freq and floor_count

[Mario Limonciello <mario.limonciello@amd.com>]

On 3/20/26 09:43, Gautham R. Shenoy wrote:
> When Floor Performance feature is supported by the platform, expose
> two sysfs files:
> 
>     * amd_pstate_floor_freq to allow userspace to request the floor
>       frequency for each CPU.
> 
>     * amd_pstate_floor_count which advertises the number of distinct
>       levels of floor frequencies supported on this platform.
> 
> Reset the floor_perf to bios_floor_perf in the suspend, offline, and
> exit paths, and restore the value to the cached user-request
> floor_freq on the resume and online paths mirroring how bios_min_perf
> is handled for MSR_AMD_CPPC_REQ.
> 
> Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
> ---
>   drivers/cpufreq/amd-pstate.c | 93 +++++++++++++++++++++++++++++++++---
>   drivers/cpufreq/amd-pstate.h |  2 +
>   2 files changed, 89 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 53b8173ff183..a068c4457a8f 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -383,8 +383,10 @@ static int amd_pstate_init_floor_perf(struct cpufreq_policy *policy)
>   			return ret;
>   	}
>   
> -	cpudata->bios_floor_perf = floor_perf;
>   
> +	cpudata->bios_floor_perf = floor_perf;

Double check the whitespace between 5 and 6; I wouldn't expect this line 
to ping pong.

> +	cpudata->floor_freq = perf_to_freq(cpudata->perf, cpudata->nominal_freq,
> +					   floor_perf);
>   	return 0;
>   }
>   
> @@ -1288,6 +1290,46 @@ static ssize_t show_energy_performance_preference(
>   	return sysfs_emit(buf, "%s\n", energy_perf_strings[preference]);
>   }
>   
> +static ssize_t store_amd_pstate_floor_freq(struct cpufreq_policy *policy,
> +					   const char *buf, size_t count)
> +{
> +	struct amd_cpudata *cpudata = policy->driver_data;
> +	union perf_cached perf = READ_ONCE(cpudata->perf);
> +	unsigned int freq;
> +	u8 floor_perf;
> +	int ret;
> +
> +	ret = kstrtouint(buf, 0, &freq);
> +	if (ret)
> +		return ret;
> +
> +	if (freq < policy->cpuinfo.min_freq || freq > policy->max)
> +		return -EINVAL;
> +
> +	floor_perf = freq_to_perf(perf, cpudata->nominal_freq, freq);
> +	ret = amd_pstate_set_floor_perf(policy, floor_perf);
> +
> +	if (!ret)
> +		cpudata->floor_freq = freq;
> +
> +	return ret ?: count;
> +}
> +
> +static ssize_t show_amd_pstate_floor_freq(struct cpufreq_policy *policy, char *buf)
> +{
> +	struct amd_cpudata *cpudata = policy->driver_data;
> +
> +	return sysfs_emit(buf, "%u\n", cpudata->floor_freq);
> +}
> +
> +static ssize_t show_amd_pstate_floor_count(struct cpufreq_policy *policy, char *buf)
> +{
> +	struct amd_cpudata *cpudata = policy->driver_data;
> +	u8 count = cpudata->floor_perf_cnt;
> +
> +	return sysfs_emit(buf, "%u\n", count);
> +}
> +
>   cpufreq_freq_attr_ro(amd_pstate_max_freq);
>   cpufreq_freq_attr_ro(amd_pstate_lowest_nonlinear_freq);
>   
> @@ -1296,6 +1338,8 @@ cpufreq_freq_attr_ro(amd_pstate_prefcore_ranking);
>   cpufreq_freq_attr_ro(amd_pstate_hw_prefcore);
>   cpufreq_freq_attr_rw(energy_performance_preference);
>   cpufreq_freq_attr_ro(energy_performance_available_preferences);
> +cpufreq_freq_attr_rw(amd_pstate_floor_freq);
> +cpufreq_freq_attr_ro(amd_pstate_floor_count);
>   
>   struct freq_attr_visibility {
>   	struct freq_attr *attr;
> @@ -1320,6 +1364,12 @@ static bool epp_visibility(void)
>   	return cppc_state == AMD_PSTATE_ACTIVE;
>   }
>   
> +/* Determines whether amd_pstate_floor_freq related attributes should be visible */
> +static bool floor_freq_visibility(void)
> +{
> +	return cpu_feature_enabled(X86_FEATURE_CPPC_PERF_PRIO);
> +}
> +
>   static struct freq_attr_visibility amd_pstate_attr_visibility[] = {
>   	{&amd_pstate_max_freq, always_visible},
>   	{&amd_pstate_lowest_nonlinear_freq, always_visible},
> @@ -1328,6 +1378,8 @@ static struct freq_attr_visibility amd_pstate_attr_visibility[] = {
>   	{&amd_pstate_hw_prefcore, prefcore_visibility},
>   	{&energy_performance_preference, epp_visibility},
>   	{&energy_performance_available_preferences, epp_visibility},
> +	{&amd_pstate_floor_freq, floor_freq_visibility},
> +	{&amd_pstate_floor_count, floor_freq_visibility},
>   };
>   
>   static struct freq_attr **get_freq_attrs(void)
> @@ -1748,24 +1800,39 @@ static int amd_pstate_epp_set_policy(struct cpufreq_policy *policy)
>   
>   static int amd_pstate_cpu_online(struct cpufreq_policy *policy)
>   {
> -	return amd_pstate_cppc_enable(policy);
> +	struct amd_cpudata *cpudata = policy->driver_data;
> +	union perf_cached perf = READ_ONCE(cpudata->perf);
> +	u8 cached_floor_perf;
> +	int ret;
> +
> +	ret = amd_pstate_cppc_enable(policy);
> +	if (ret)
> +		return ret;
> +
> +	cached_floor_perf = freq_to_perf(perf, cpudata->nominal_freq, cpudata->floor_freq);
> +	return amd_pstate_set_floor_perf(policy, cached_floor_perf);
>   }
>   
>   static int amd_pstate_cpu_offline(struct cpufreq_policy *policy)
>   {
>   	struct amd_cpudata *cpudata = policy->driver_data;
>   	union perf_cached perf = READ_ONCE(cpudata->perf);
> +	int ret;
>   
>   	/*
>   	 * Reset CPPC_REQ MSR to the BIOS value, this will allow us to retain the BIOS specified
>   	 * min_perf value across kexec reboots. If this CPU is just onlined normally after this, the
>   	 * limits, epp and desired perf will get reset to the cached values in cpudata struct
>   	 */
> -	return amd_pstate_update_perf(policy, perf.bios_min_perf,
> +	ret = amd_pstate_update_perf(policy, perf.bios_min_perf,
>   				     FIELD_GET(AMD_CPPC_DES_PERF_MASK, cpudata->cppc_req_cached),
>   				     FIELD_GET(AMD_CPPC_MAX_PERF_MASK, cpudata->cppc_req_cached),
>   				     FIELD_GET(AMD_CPPC_EPP_PERF_MASK, cpudata->cppc_req_cached),
>   				     false);
> +	if (ret)
> +		return ret;
> +
> +	return amd_pstate_set_floor_perf(policy, cpudata->bios_floor_perf);
>   }
>   
>   static int amd_pstate_suspend(struct cpufreq_policy *policy)
> @@ -1787,6 +1854,10 @@ static int amd_pstate_suspend(struct cpufreq_policy *policy)
>   	if (ret)
>   		return ret;
>   
> +	ret = amd_pstate_set_floor_perf(policy, cpudata->bios_floor_perf);
> +	if (ret)
> +		return ret;
> +
>   	/* set this flag to avoid setting core offline*/
>   	cpudata->suspended = true;
>   
> @@ -1798,15 +1869,24 @@ static int amd_pstate_resume(struct cpufreq_policy *policy)
>   	struct amd_cpudata *cpudata = policy->driver_data;
>   	union perf_cached perf = READ_ONCE(cpudata->perf);
>   	int cur_perf = freq_to_perf(perf, cpudata->nominal_freq, policy->cur);
> +	u8 cached_floor_perf;
> +	int ret;
>   
>   	/* Set CPPC_REQ to last sane value until the governor updates it */
> -	return amd_pstate_update_perf(policy, perf.min_limit_perf, cur_perf, perf.max_limit_perf,
> -				      0U, false);
> +	ret = amd_pstate_update_perf(policy, perf.min_limit_perf, cur_perf, perf.max_limit_perf,
> +				     0U, false);
> +	if (ret)
> +		return ret;
> +
> +	cached_floor_perf = freq_to_perf(perf, cpudata->nominal_freq, cpudata->floor_freq);
> +	return amd_pstate_set_floor_perf(policy, cached_floor_perf);
>   }
>   
>   static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
>   {
>   	struct amd_cpudata *cpudata = policy->driver_data;
> +	union perf_cached perf = READ_ONCE(cpudata->perf);
> +	u8 cached_floor_perf;
>   
>   	if (cpudata->suspended) {
>   		int ret;
> @@ -1819,7 +1899,8 @@ static int amd_pstate_epp_resume(struct cpufreq_policy *policy)
>   		cpudata->suspended = false;
>   	}
>   
> -	return 0;
> +	cached_floor_perf = freq_to_perf(perf, cpudata->nominal_freq, cpudata->floor_freq);
> +	return amd_pstate_set_floor_perf(policy, cached_floor_perf);
>   }
>   
>   static struct cpufreq_driver amd_pstate_driver = {
> diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
> index f04561da4518..2f7a96836fcd 100644
> --- a/drivers/cpufreq/amd-pstate.h
> +++ b/drivers/cpufreq/amd-pstate.h
> @@ -72,6 +72,7 @@ struct amd_aperf_mperf {
>    * @max_limit_freq: Cached value of policy->max (in khz)
>    * @nominal_freq: the frequency (in khz) that mapped to nominal_perf
>    * @lowest_nonlinear_freq: the frequency (in khz) that mapped to lowest_nonlinear_perf
> + * @floor_freq: Cached value of the user requested floor_freq
>    * @cur: Difference of Aperf/Mperf/tsc count between last and current sample
>    * @prev: Last Aperf/Mperf/tsc count value read from register
>    * @freq: current cpu frequency value (in khz)
> @@ -101,6 +102,7 @@ struct amd_cpudata {
>   	u32	max_limit_freq;
>   	u32	nominal_freq;
>   	u32	lowest_nonlinear_freq;
> +	u32	floor_freq;
>   
>   	struct amd_aperf_mperf cur;
>   	struct amd_aperf_mperf prev;