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Message-ID: <1f8d08e5-8bc7-4a1a-a00b-505394a451bb@amd.com>
Date: Tue, 15 Apr 2025 15:54:21 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Dhananjay Ugwekar <dhananjay.ugwekar@....com>, gautham.shenoy@....com
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] cpufreq/amd-pstate: Add support for the "Requested
CPU Min frequency" BIOS option
On 4/15/2025 5:21 AM, Dhananjay Ugwekar wrote:
> Initialize lower frequency limit to the "Requested CPU Min frequency"
> BIOS option (if it is set) value as part of the driver->init()
> callback. The BIOS specified value is passed by the PMFW as min_perf in
> CPPC_REQ MSR. To ensure that we don't mistake a stale min_perf value in
> CPPC_REQ value as the "Requested CPU Min frequency" during a kexec wakeup,
> reset the CPPC_REQ.min_perf value back to the BIOS specified one in the
> offline, exit and suspend callbacks.
>
> amd_pstate_target() and amd_pstate_epp_update_limit() which are invoked
> as part of the resume() and online() callbacks will take care of restoring
> the CPPC_REQ back to the latest sane values.
>
> Signed-off-by: Dhananjay Ugwekar <dhananjay.ugwekar@....com>
I'm generally fine with this, but I have one nit below.
> ---
> drivers/cpufreq/amd-pstate.c | 62 ++++++++++++++++++++++++++++--------
> drivers/cpufreq/amd-pstate.h | 2 ++
> 2 files changed, 51 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 02de51001eba..d94fd2a38990 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -389,7 +389,8 @@ static inline int amd_pstate_cppc_enable(struct cpufreq_policy *policy)
> static int msr_init_perf(struct amd_cpudata *cpudata)
> {
> union perf_cached perf = READ_ONCE(cpudata->perf);
> - u64 cap1, numerator;
> + u64 cap1, numerator, cppc_req;
> + u8 min_perf;
>
> int ret = rdmsrl_safe_on_cpu(cpudata->cpu, MSR_AMD_CPPC_CAP1,
> &cap1);
> @@ -400,6 +401,22 @@ static int msr_init_perf(struct amd_cpudata *cpudata)
> if (ret)
> return ret;
>
> + ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, &cppc_req);
> + if (ret)
> + return ret;
> +
> + WRITE_ONCE(cpudata->cppc_req_cached, cppc_req);
> + min_perf = FIELD_GET(AMD_CPPC_MIN_PERF_MASK, cppc_req);
> +
> + /*
> + * Clear out the min_perf part to check if the rest of the MSR is 0, if yes, this is an
> + * indication that the min_perf value is the one specified through the BIOS option
> + */
> + cppc_req &= ~(AMD_CPPC_MIN_PERF_MASK);
> +
> + if (!cppc_req && min_perf)
> + perf.bios_min_perf = min_perf;
To avoid a risk of garbage being in perf.bios_min_perf leading to hard
to root cause bugs could we initialize this to 0 in the non
bios_min_perf case?
something like this:
cppc_req &= ~(AMD_CPPC_MIN_PERF_MASK);
perf.bios_min_perf = (!cppc_req && min_perf) ? min_perf : 0;
> +
> perf.highest_perf = numerator;
> perf.max_limit_perf = numerator;
> perf.min_limit_perf = FIELD_GET(AMD_CPPC_LOWEST_PERF_MASK, cap1);
> @@ -580,20 +597,26 @@ static int amd_pstate_verify(struct cpufreq_policy_data *policy_data)
> {
> /*
> * Initialize lower frequency limit (i.e.policy->min) with
> - * lowest_nonlinear_frequency which is the most energy efficient
> - * frequency. Override the initial value set by cpufreq core and
> - * amd-pstate qos_requests.
> + * lowest_nonlinear_frequency or the min frequency (if) specified in BIOS,
> + * Override the initial value set by cpufreq core and amd-pstate qos_requests.
> */
> if (policy_data->min == FREQ_QOS_MIN_DEFAULT_VALUE) {
> struct cpufreq_policy *policy __free(put_cpufreq_policy) =
> cpufreq_cpu_get(policy_data->cpu);
> struct amd_cpudata *cpudata;
> + union perf_cached perf;
>
> if (!policy)
> return -EINVAL;
>
> cpudata = policy->driver_data;
> - policy_data->min = cpudata->lowest_nonlinear_freq;
> + perf = READ_ONCE(cpudata->perf);
> +
> + if (perf.bios_min_perf)
> + policy_data->min = perf_to_freq(perf, cpudata->nominal_freq,
> + perf.bios_min_perf);
> + else
> + policy_data->min = cpudata->lowest_nonlinear_freq;
> }
>
> cpufreq_verify_within_cpu_limits(policy_data);
> @@ -1041,6 +1064,9 @@ static void amd_pstate_cpu_exit(struct cpufreq_policy *policy)
> {
> struct amd_cpudata *cpudata = policy->driver_data;
>
> + /* Reset CPPC_REQ MSR to the BIOS value */
> + amd_pstate_update_perf(policy, cpudata->perf.bios_min_perf, 0U, 0U, 0U, false);
> +
> freq_qos_remove_request(&cpudata->req[1]);
> freq_qos_remove_request(&cpudata->req[0]);
> policy->fast_switch_possible = false;
> @@ -1428,7 +1454,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
> struct amd_cpudata *cpudata;
> union perf_cached perf;
> struct device *dev;
> - u64 value;
> int ret;
>
> /*
> @@ -1493,12 +1518,6 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
> cpudata->epp_default = AMD_CPPC_EPP_BALANCE_PERFORMANCE;
> }
>
> - if (cpu_feature_enabled(X86_FEATURE_CPPC)) {
> - ret = rdmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ, &value);
> - if (ret)
> - return ret;
> - WRITE_ONCE(cpudata->cppc_req_cached, value);
> - }
> ret = amd_pstate_set_epp(policy, cpudata->epp_default);
> if (ret)
> return ret;
> @@ -1518,6 +1537,9 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
> struct amd_cpudata *cpudata = policy->driver_data;
>
> if (cpudata) {
> + /* Reset CPPC_REQ MSR to the BIOS value */
> + amd_pstate_update_perf(policy, cpudata->perf.bios_min_perf, 0U, 0U, 0U, false);
> +
> kfree(cpudata);
> policy->driver_data = NULL;
> }
> @@ -1575,13 +1597,27 @@ static int amd_pstate_cpu_online(struct cpufreq_policy *policy)
>
> static int amd_pstate_cpu_offline(struct cpufreq_policy *policy)
> {
> - return 0;
> + struct amd_cpudata *cpudata = policy->driver_data;
> +
> + /*
> + * 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, cpudata->perf.bios_min_perf, 0U, 0U, 0U, false);
> }
>
> static int amd_pstate_suspend(struct cpufreq_policy *policy)
> {
> struct amd_cpudata *cpudata = policy->driver_data;
>
> + /*
> + * 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 resumed back without kexec,
> + * the limits, epp and desired perf will get reset to the cached values in cpudata struct
> + */
> + amd_pstate_update_perf(policy, cpudata->perf.bios_min_perf, 0U, 0U, 0U, false);
> +
> /* invalidate to ensure it's rewritten during resume */
> cpudata->cppc_req_cached = 0;
>
> diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
> index fbe1c08d3f06..2f7ae364d331 100644
> --- a/drivers/cpufreq/amd-pstate.h
> +++ b/drivers/cpufreq/amd-pstate.h
> @@ -30,6 +30,7 @@
> * @lowest_perf: the absolute lowest performance level of the processor
> * @min_limit_perf: Cached value of the performance corresponding to policy->min
> * @max_limit_perf: Cached value of the performance corresponding to policy->max
> + * @bios_min_perf: Cached perf value corresponding to the "Requested CPU Min Frequency" BIOS option
> */
> union perf_cached {
> struct {
> @@ -39,6 +40,7 @@ union perf_cached {
> u8 lowest_perf;
> u8 min_limit_perf;
> u8 max_limit_perf;
> + u8 bios_min_perf;
> };
> u64 val;
> };
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