Re: [PATCH v5 06/22] cpufreq: amd: introduce a new amd pstate driver to support future processors

[Rafael J. Wysocki]

On Tue, Nov 30, 2021 at 1:37 PM Huang Rui <ray.huang@xxxxxxx> wrote:
>
> amd-pstate is the AMD CPU performance scaling driver that introduces a
> new CPU frequency control mechanism on AMD Zen based CPU series in Linux
> kernel. The new mechanism is based on Collaborative processor
> performance control (CPPC) which is finer grain frequency management
> than legacy ACPI hardware P-States. Current AMD CPU platforms are using
> the ACPI P-states driver to manage CPU frequency and clocks with
> switching only in 3 P-states. AMD P-States is to replace the ACPI
> P-states controls, allows a flexible, low-latency interface for the
> Linux kernel to directly communicate the performance hints to hardware.
>
> "amd-pstate" leverages the Linux kernel governors such as *schedutil*,
> *ondemand*, etc. to manage the performance hints which are provided by CPPC
> hardware functionality. The first version for amd-pstate is to support one
> of the Zen3 processors, and we will support more in future after we verify
> the hardware and SBIOS functionalities.
>
> There are two types of hardware implementations for amd-pstate: one is full
> MSR support and another is shared memory support. It can use
> X86_FEATURE_CPPC feature flag to distinguish the different types.
>
> Using the new AMD P-States method + kernel governors (*schedutil*,
> *ondemand*, ...) to manage the frequency update is the most appropriate
> bridge between AMD Zen based hardware processor and Linux kernel, the
> processor is able to adjust to the most efficiency frequency according to
> the kernel scheduler loading.
>
> Please check the detailed CPU feature and MSR register description in
> Processor Programming Reference (PPR) for AMD Family 19h Model 51h,
> Revision A1 Processors:
>
> https://www.amd.com/system/files/TechDocs/56569-A1-PUB.zip
>
> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
> ---
>  drivers/cpufreq/Kconfig.x86  |  17 ++
>  drivers/cpufreq/Makefile     |   1 +
>  drivers/cpufreq/amd-pstate.c | 398 +++++++++++++++++++++++++++++++++++
>  3 files changed, 416 insertions(+)
>  create mode 100644 drivers/cpufreq/amd-pstate.c
>
> diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> index 92701a18bdd9..21837eb1698b 100644
> --- a/drivers/cpufreq/Kconfig.x86
> +++ b/drivers/cpufreq/Kconfig.x86
> @@ -34,6 +34,23 @@ config X86_PCC_CPUFREQ
>
>           If in doubt, say N.
>
> +config X86_AMD_PSTATE
> +       tristate "AMD Processor P-State driver"
> +       depends on X86
> +       select ACPI_PROCESSOR if ACPI
> +       select ACPI_CPPC_LIB if X86_64 && ACPI
> +       select CPU_FREQ_GOV_SCHEDUTIL if SMP
> +       help
> +         This driver adds a CPUFreq driver which utilizes a fine grain
> +         processor performance frequency control range instead of legacy
> +         performance levels. This driver supports the AMD processors with
> +         _CPC object in the SBIOS.

Well, _CPC needs to be present in the ACPI tables of the system.

> +
> +         For details, take a look at:
> +         <file:Documentation/admin-guide/pm/amd-pstate.rst>.
> +
> +         If in doubt, say N.
> +
>  config X86_ACPI_CPUFREQ
>         tristate "ACPI Processor P-States driver"
>         depends on ACPI_PROCESSOR
> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> index 48ee5859030c..c8d307010922 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -25,6 +25,7 @@ obj-$(CONFIG_CPUFREQ_DT_PLATDEV)      += cpufreq-dt-platdev.o
>  # speedstep-* is preferred over p4-clockmod.
>
>  obj-$(CONFIG_X86_ACPI_CPUFREQ)         += acpi-cpufreq.o
> +obj-$(CONFIG_X86_AMD_PSTATE)           += amd-pstate.o
>  obj-$(CONFIG_X86_POWERNOW_K8)          += powernow-k8.o
>  obj-$(CONFIG_X86_PCC_CPUFREQ)          += pcc-cpufreq.o
>  obj-$(CONFIG_X86_POWERNOW_K6)          += powernow-k6.o
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> new file mode 100644
> index 000000000000..20ffbc30118f
> --- /dev/null
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -0,0 +1,398 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * amd-pstate.c - AMD Processor P-state Frequency Driver
> + *
> + * Copyright (C) 2021 Advanced Micro Devices, Inc. All Rights Reserved.
> + *
> + * Author: Huang Rui <ray.huang@xxxxxxx>

Given the lack of other documentation, it would be nice to provide at
least a brief description of the driver here.

> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/smp.h>
> +#include <linux/sched.h>
> +#include <linux/cpufreq.h>
> +#include <linux/compiler.h>
> +#include <linux/dmi.h>
> +#include <linux/slab.h>
> +#include <linux/acpi.h>
> +#include <linux/io.h>
> +#include <linux/delay.h>
> +#include <linux/uaccess.h>
> +#include <linux/static_call.h>
> +
> +#include <acpi/processor.h>
> +#include <acpi/cppc_acpi.h>
> +
> +#include <asm/msr.h>
> +#include <asm/processor.h>
> +#include <asm/cpufeature.h>
> +#include <asm/cpu_device_id.h>
> +
> +#define AMD_PSTATE_TRANSITION_LATENCY  0x20000
> +#define AMD_PSTATE_TRANSITION_DELAY    500
> +
> +static struct cpufreq_driver amd_pstate_driver;
> +
> +struct amd_cpudata {
> +       int     cpu;
> +
> +       struct freq_qos_request req[2];
> +
> +       u64     cppc_req_cached;
> +
> +       u32     highest_perf;
> +       u32     nominal_perf;
> +       u32     lowest_nonlinear_perf;
> +       u32     lowest_perf;
> +
> +       u32     max_freq;
> +       u32     min_freq;
> +       u32     nominal_freq;
> +       u32     lowest_nonlinear_freq;
> +};

Please describe the fields of this structure, preferably in a kerneldoc comment.

> +
> +static inline int pstate_enable(bool enable)
> +{
> +       return wrmsrl_safe(MSR_AMD_CPPC_ENABLE, enable);
> +}
> +
> +DEFINE_STATIC_CALL(amd_pstate_enable, pstate_enable);

Why do you need a static call here?

It doesn't get updated anywhere below.

> +
> +static inline int amd_pstate_enable(bool enable)
> +{
> +       return static_call(amd_pstate_enable)(enable);
> +}
> +
> +static int pstate_init_perf(struct amd_cpudata *cpudata)
> +{
> +       u64 cap1;
> +
> +       int ret = rdmsrl_safe_on_cpu(cpudata->cpu, MSR_AMD_CPPC_CAP1,
> +                                    &cap1);
> +       if (ret)
> +               return ret;
> +
> +       /*
> +        * TODO: Introduce AMD specific power feature.
> +        *
> +        * CPPC entry doesn't indicate the highest performance in some ASICs.
> +        */
> +       WRITE_ONCE(cpudata->highest_perf, amd_get_highest_perf());
> +
> +       WRITE_ONCE(cpudata->nominal_perf, CAP1_NOMINAL_PERF(cap1));
> +       WRITE_ONCE(cpudata->lowest_nonlinear_perf, CAP1_LOWNONLIN_PERF(cap1));
> +       WRITE_ONCE(cpudata->lowest_perf, CAP1_LOWEST_PERF(cap1));
> +
> +       return 0;
> +}
> +
> +DEFINE_STATIC_CALL(amd_pstate_init_perf, pstate_init_perf);

And same here.

> +
> +static inline int amd_pstate_init_perf(struct amd_cpudata *cpudata)
> +{
> +       return static_call(amd_pstate_init_perf)(cpudata);
> +}
> +
> +static void pstate_update_perf(struct amd_cpudata *cpudata, u32 min_perf,
> +                              u32 des_perf, u32 max_perf, bool fast_switch)
> +{
> +       if (fast_switch)
> +               wrmsrl(MSR_AMD_CPPC_REQ, READ_ONCE(cpudata->cppc_req_cached));
> +       else
> +               wrmsrl_on_cpu(cpudata->cpu, MSR_AMD_CPPC_REQ,
> +                             READ_ONCE(cpudata->cppc_req_cached));
> +}
> +
> +DEFINE_STATIC_CALL(amd_pstate_update_perf, pstate_update_perf);

Same here.

> +
> +static inline void amd_pstate_update_perf(struct amd_cpudata *cpudata,
> +                                         u32 min_perf, u32 des_perf,
> +                                         u32 max_perf, bool fast_switch)
> +{
> +       static_call(amd_pstate_update_perf)(cpudata, min_perf, des_perf,
> +                                           max_perf, fast_switch);
> +}
> +
> +static void amd_pstate_update(struct amd_cpudata *cpudata, u32 min_perf,
> +                             u32 des_perf, u32 max_perf, bool fast_switch)
> +{
> +       u64 prev = READ_ONCE(cpudata->cppc_req_cached);
> +       u64 value = prev;
> +
> +       value &= ~REQ_MIN_PERF(~0L);
> +       value |= REQ_MIN_PERF(min_perf);
> +
> +       value &= ~REQ_DES_PERF(~0L);
> +       value |= REQ_DES_PERF(des_perf);
> +
> +       value &= ~REQ_MAX_PERF(~0L);
> +       value |= REQ_MAX_PERF(max_perf);
> +
> +       if (value == prev)
> +               return;
> +
> +       WRITE_ONCE(cpudata->cppc_req_cached, value);
> +
> +       amd_pstate_update_perf(cpudata, min_perf, des_perf,
> +                              max_perf, fast_switch);
> +}
> +
> +static int amd_pstate_verify(struct cpufreq_policy_data *policy)
> +{
> +       cpufreq_verify_within_cpu_limits(policy);
> +
> +       return 0;
> +}
> +
> +static int amd_pstate_target(struct cpufreq_policy *policy,
> +                            unsigned int target_freq,
> +                            unsigned int relation)
> +{
> +       struct cpufreq_freqs freqs;
> +       struct amd_cpudata *cpudata = policy->driver_data;
> +       unsigned long max_perf, min_perf, des_perf, cap_perf;
> +
> +       if (!cpudata->max_freq)
> +               return -ENODEV;
> +
> +       cap_perf = READ_ONCE(cpudata->highest_perf);
> +       min_perf = READ_ONCE(cpudata->lowest_nonlinear_perf);
> +       max_perf = cap_perf;
> +
> +       freqs.old = policy->cur;
> +       freqs.new = target_freq;
> +
> +       des_perf = DIV_ROUND_CLOSEST(target_freq * cap_perf,
> +                                    cpudata->max_freq);
> +
> +       cpufreq_freq_transition_begin(policy, &freqs);
> +       amd_pstate_update(cpudata, min_perf, des_perf,
> +                         max_perf, false);
> +       cpufreq_freq_transition_end(policy, &freqs, false);
> +
> +       return 0;
> +}
> +
> +static int amd_get_min_freq(struct amd_cpudata *cpudata)
> +{
> +       struct cppc_perf_caps cppc_perf;
> +
> +       int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
> +       if (ret)
> +               return ret;
> +
> +       /* Switch to khz */
> +       return cppc_perf.lowest_freq * 1000;
> +}
> +
> +static int amd_get_max_freq(struct amd_cpudata *cpudata)
> +{
> +       struct cppc_perf_caps cppc_perf;
> +       u32 max_perf, max_freq, nominal_freq, nominal_perf;
> +       u64 boost_ratio;
> +
> +       int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
> +       if (ret)
> +               return ret;
> +
> +       nominal_freq = cppc_perf.nominal_freq;
> +       nominal_perf = READ_ONCE(cpudata->nominal_perf);
> +       max_perf = READ_ONCE(cpudata->highest_perf);
> +
> +       boost_ratio = div_u64(max_perf << SCHED_CAPACITY_SHIFT,
> +                             nominal_perf);
> +
> +       max_freq = nominal_freq * boost_ratio >> SCHED_CAPACITY_SHIFT;
> +
> +       /* Switch to khz */
> +       return max_freq * 1000;
> +}
> +
> +static int amd_get_nominal_freq(struct amd_cpudata *cpudata)
> +{
> +       struct cppc_perf_caps cppc_perf;
> +
> +       int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
> +       if (ret)
> +               return ret;
> +
> +       /* Switch to khz */
> +       return cppc_perf.nominal_freq * 1000;
> +}
> +
> +static int amd_get_lowest_nonlinear_freq(struct amd_cpudata *cpudata)
> +{
> +       struct cppc_perf_caps cppc_perf;
> +       u32 lowest_nonlinear_freq, lowest_nonlinear_perf,
> +           nominal_freq, nominal_perf;
> +       u64 lowest_nonlinear_ratio;
> +
> +       int ret = cppc_get_perf_caps(cpudata->cpu, &cppc_perf);
> +       if (ret)
> +               return ret;
> +
> +       nominal_freq = cppc_perf.nominal_freq;
> +       nominal_perf = READ_ONCE(cpudata->nominal_perf);
> +
> +       lowest_nonlinear_perf = cppc_perf.lowest_nonlinear_perf;
> +
> +       lowest_nonlinear_ratio = div_u64(lowest_nonlinear_perf << SCHED_CAPACITY_SHIFT,
> +                                        nominal_perf);
> +
> +       lowest_nonlinear_freq = nominal_freq * lowest_nonlinear_ratio >> SCHED_CAPACITY_SHIFT;
> +
> +       /* Switch to khz */
> +       return lowest_nonlinear_freq * 1000;
> +}
> +
> +static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
> +{
> +       int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
> +       struct device *dev;
> +       struct amd_cpudata *cpudata;
> +
> +       dev = get_cpu_device(policy->cpu);
> +       if (!dev)
> +               return -ENODEV;
> +
> +       cpudata = kzalloc(sizeof(*cpudata), GFP_KERNEL);
> +       if (!cpudata)
> +               return -ENOMEM;
> +
> +       cpudata->cpu = policy->cpu;
> +
> +       ret = amd_pstate_init_perf(cpudata);
> +       if (ret)
> +               goto free_cpudata1;
> +
> +       min_freq = amd_get_min_freq(cpudata);
> +       max_freq = amd_get_max_freq(cpudata);
> +       nominal_freq = amd_get_nominal_freq(cpudata);
> +       lowest_nonlinear_freq = amd_get_lowest_nonlinear_freq(cpudata);
> +
> +       if (min_freq < 0 || max_freq < 0 || min_freq > max_freq) {
> +               dev_err(dev, "min_freq(%d) or max_freq(%d) value is incorrect\n",
> +                       min_freq, max_freq);
> +               ret = -EINVAL;
> +               goto free_cpudata1;
> +       }
> +
> +       policy->cpuinfo.transition_latency = AMD_PSTATE_TRANSITION_LATENCY;
> +       policy->transition_delay_us = AMD_PSTATE_TRANSITION_DELAY;
> +
> +       policy->min = min_freq;
> +       policy->max = max_freq;
> +
> +       policy->cpuinfo.min_freq = min_freq;
> +       policy->cpuinfo.max_freq = max_freq;
> +
> +       /* It will be updated by governor */
> +       policy->cur = policy->cpuinfo.min_freq;

The freq_qos requests below are never updated in this file.  What are they for?

> +
> +       ret = freq_qos_add_request(&policy->constraints, &cpudata->req[0],
> +                                  FREQ_QOS_MIN, policy->cpuinfo.min_freq);
> +       if (ret < 0) {
> +               dev_err(dev, "Failed to add min-freq constraint (%d)\n", ret);
> +               goto free_cpudata1;
> +       }
> +
> +       ret = freq_qos_add_request(&policy->constraints, &cpudata->req[1],
> +                                  FREQ_QOS_MAX, policy->cpuinfo.max_freq);
> +       if (ret < 0) {
> +               dev_err(dev, "Failed to add max-freq constraint (%d)\n", ret);
> +               goto free_cpudata2;
> +       }
> +
> +       /* Initial processor data capability frequencies */
> +       cpudata->max_freq = max_freq;
> +       cpudata->min_freq = min_freq;
> +       cpudata->nominal_freq = nominal_freq;
> +       cpudata->lowest_nonlinear_freq = lowest_nonlinear_freq;
> +
> +       policy->driver_data = cpudata;
> +
> +       return 0;
> +
> +free_cpudata2:
> +       freq_qos_remove_request(&cpudata->req[0]);
> +free_cpudata1:
> +       kfree(cpudata);
> +       return ret;
> +}
> +
> +static int amd_pstate_cpu_exit(struct cpufreq_policy *policy)
> +{
> +       struct amd_cpudata *cpudata;
> +
> +       cpudata = policy->driver_data;
> +
> +       freq_qos_remove_request(&cpudata->req[1]);
> +       freq_qos_remove_request(&cpudata->req[0]);
> +       kfree(cpudata);
> +
> +       return 0;
> +}
> +
> +static struct cpufreq_driver amd_pstate_driver = {
> +       .flags          = CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
> +       .verify         = amd_pstate_verify,
> +       .target         = amd_pstate_target,
> +       .init           = amd_pstate_cpu_init,
> +       .exit           = amd_pstate_cpu_exit,
> +       .name           = "amd-pstate",
> +};
> +
> +static int __init amd_pstate_init(void)
> +{
> +       int ret;
> +
> +       if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
> +               return -ENODEV;
> +
> +       if (!acpi_cpc_valid()) {
> +               pr_debug("the _CPC object is not present in SBIOS\n");
> +               return -ENODEV;
> +       }
> +
> +       /* don't keep reloading if cpufreq_driver exists */
> +       if (cpufreq_get_current_driver())
> +               return -EEXIST;
> +
> +       /* capability check */
> +       if (!boot_cpu_has(X86_FEATURE_CPPC)) {
> +               pr_debug("AMD CPPC MSR based functionality is not supported\n");
> +               return -ENODEV;
> +       }
> +
> +       /* enable amd pstate feature */
> +       ret = amd_pstate_enable(true);
> +       if (ret) {
> +               pr_err("failed to enable amd-pstate with return %d\n", ret);
> +               return ret;
> +       }
> +
> +       ret = cpufreq_register_driver(&amd_pstate_driver);
> +       if (ret)
> +               pr_err("failed to register amd_pstate_driver with return %d\n",
> +                      ret);
> +
> +       return ret;
> +}
> +
> +static void __exit amd_pstate_exit(void)
> +{
> +       cpufreq_unregister_driver(&amd_pstate_driver);
> +
> +       amd_pstate_enable(false);
> +}
> +
> +module_init(amd_pstate_init);
> +module_exit(amd_pstate_exit);
> +
> +MODULE_AUTHOR("Huang Rui <ray.huang@xxxxxxx>");
> +MODULE_DESCRIPTION("AMD Processor P-state Frequency Driver");
> +MODULE_LICENSE("GPL");
> --
> 2.25.1
>