RE: [PATCH v3 1/8] ACPI: CPPC: Add AMD pstate energy performance preference cppc control

["Yuan, Perry" <Perry.Yuan@amd.com>]

[AMD Official Use Only - General]



> -----Original Message-----
> From: Rafael J. Wysocki <rafael@kernel.org>
> Sent: Thursday, November 10, 2022 10:50 PM
> To: Limonciello, Mario <Mario.Limonciello@amd.com>; Yuan, Perry
> <Perry.Yuan@amd.com>
> Cc: rafael.j.wysocki@intel.com; Huang, Ray <Ray.Huang@amd.com>;
> viresh.kumar@linaro.org; Sharma, Deepak <Deepak.Sharma@amd.com>;
> Fontenot, Nathan <Nathan.Fontenot@amd.com>; Deucher, Alexander
> <Alexander.Deucher@amd.com>; Huang, Shimmer
> <Shimmer.Huang@amd.com>; Du, Xiaojian <Xiaojian.Du@amd.com>; Meng,
> Li (Jassmine) <Li.Meng@amd.com>; linux-pm@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH v3 1/8] ACPI: CPPC: Add AMD pstate energy
> performance preference cppc control
> 
> Caution: This message originated from an External Source. Use proper
> caution when opening attachments, clicking links, or responding.
> 
> 
> On Mon, Nov 7, 2022 at 7:44 PM Limonciello, Mario
> <mario.limonciello@amd.com> wrote:
> >
> > On 11/7/2022 11:56, Perry Yuan wrote:
> > > Add the EPP(Energy Performance Preference) support for the AMD SoCs
> > > without the dedicated CPPC MSR, those SoCs need to add this cppc
> > > acpi functions to update EPP values and desired perf value.
> >
> > As far as I can tell this is generic code.  Although the reason you're
> > submitting it is for enabling AMD SoCs, the commit message should be
> > worded as such.
> >
> > >
> > > In order to get EPP worked, cppc_get_epp_caps() will query EPP
> > > preference value and cppc_set_epp_perf() will set EPP new value.
> > > Before the EPP works, pstate driver will use cppc_set_auto_epp() to
> > > enable EPP function from firmware firstly.
> >
> > This could more succinctly say:
> >
> > "Add support for setting and querying EPP preferences to the generic
> > CPPC driver.  This enables downstream drivers such as amd-pstate to
> > discover and use these values."
> >
> > >
> > > Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
> > > ---
> > >   drivers/acpi/cppc_acpi.c | 126
> +++++++++++++++++++++++++++++++++++++++
> > >   include/acpi/cppc_acpi.h |  17 ++++++
> > >   2 files changed, 143 insertions(+)
> > >
> > > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> > > index 093675b1a1ff..d9c38dee1f48 100644
> > > --- a/drivers/acpi/cppc_acpi.c
> > > +++ b/drivers/acpi/cppc_acpi.c
> > > @@ -1365,6 +1365,132 @@ int cppc_get_perf_ctrs(int cpunum, struct
> cppc_perf_fb_ctrs *perf_fb_ctrs)
> > >   }
> > >   EXPORT_SYMBOL_GPL(cppc_get_perf_ctrs);
> > >
> > > +/**
> > > + * cppc_get_epp_caps - Get the energy preference register value.
> > > + * @cpunum: CPU from which to get epp preference level.
> > > + * @perf_caps: Return address.
> > > + *
> > > + * Return: 0 for success, -EIO otherwise.
> > > + */
> > > +int cppc_get_epp_caps(int cpunum, struct cppc_perf_caps *perf_caps)
> > > +{
> > > +     struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
> > > +     struct cpc_register_resource *energy_perf_reg;
> > > +     u64 energy_perf;
> > > +
> > > +     if (!cpc_desc) {
> > > +             pr_warn("No CPC descriptor for CPU:%d\n", cpunum);
> > > +             return -ENODEV;
> > > +     }
> > > +
> > > +     energy_perf_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
> > > +
> > > +     if (!CPC_SUPPORTED(energy_perf_reg))
> > > +             pr_warn("energy perf reg update is unsupported!\n");
> >
> > No need to add a explanation point at the end.
> >
> > As this is a per-CPU message I wonder if this would be better as
> > pr_warn_once()?  Othewrise some systems with large numbers of cores
> > might potentially show this message quite a few times.
> 
> pr_info_once() would suffice IMO.

Fixed in V4. 

> 
> > > +
> > > +     if (CPC_IN_PCC(energy_perf_reg)) {
> > > +             int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);
> > > +             struct cppc_pcc_data *pcc_ss_data = NULL;
> > > +             int ret = 0;
> > > +
> > > +             if (pcc_ss_id < 0)
> > > +                     return -ENODEV;
> > > +
> > > +             pcc_ss_data = pcc_data[pcc_ss_id];
> > > +
> > > +             down_write(&pcc_ss_data->pcc_lock);
> > > +
> > > +             if (send_pcc_cmd(pcc_ss_id, CMD_READ) >= 0) {
> > > +                     cpc_read(cpunum, energy_perf_reg, &energy_perf);
> > > +                     perf_caps->energy_perf = energy_perf;
> > > +             } else {
> > > +                     ret = -EIO;
> > > +             }
> > > +
> > > +             up_write(&pcc_ss_data->pcc_lock);
> > > +
> > > +             return ret;
> > > +     }
> 
> What if CPC is not in PCC?
> 
> Would returning 0 then work for all users?

Fixed in V4

> 
> > > +
> > > +     return 0;
> > > +}
> > > +EXPORT_SYMBOL_GPL(cppc_get_epp_caps);
> > > +
> > > +int cppc_set_auto_epp(int cpu, bool enable) {
> > > +     int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
> > > +     struct cpc_register_resource *auto_sel_reg;
> > > +     struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> > > +     struct cppc_pcc_data *pcc_ss_data = NULL;
> > > +     int ret = -EINVAL;
> > > +
> > > +     if (!cpc_desc) {
> > > +             pr_warn("No CPC descriptor for CPU:%d\n", cpu);
> >
> > Is this actually warn worthy?  I would think it's fine a debug like we
> > have for the other _CPC missing messages.
> >
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
> > > +
> > > +     if (CPC_IN_PCC(auto_sel_reg)) {
> > > +             if (pcc_ss_id < 0)
> > > +                     return -ENODEV;
> > > +
> > > +             ret = cpc_write(cpu, auto_sel_reg, enable);
> > > +             if (ret)
> > > +                     return ret;
> > > +
> > > +             pcc_ss_data = pcc_data[pcc_ss_id];
> > > +
> > > +             down_write(&pcc_ss_data->pcc_lock);
> > > +             /* after writing CPC, transfer the ownership of PCC to platform */
> > > +             ret = send_pcc_cmd(pcc_ss_id, CMD_WRITE);
> > > +             up_write(&pcc_ss_data->pcc_lock);
> > > +             return ret;
> > > +     }
> > > +
> > > +     return cpc_write(cpu, auto_sel_reg, enable); }
> > > +EXPORT_SYMBOL_GPL(cppc_set_auto_epp);
> > > +
> > > +/*
> > > + * Set Energy Performance Preference Register value through
> > > + * Performance Controls Interface
> > > + */
> > > +int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
> > > +{
> > > +     int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
> > > +     struct cpc_register_resource *epp_set_reg;
> > > +     struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> > > +     struct cppc_pcc_data *pcc_ss_data = NULL;
> > > +     int ret = -EINVAL;
> > > +
> > > +     if (!cpc_desc) {
> > > +             pr_warn("No CPC descriptor for CPU:%d\n", cpu);
> >
> > Is this actually warn worthy?  I would think it's fine a debug like we
> > have for the other _CPC missing messages.
> >
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     epp_set_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
> > > +
> > > +     if (CPC_IN_PCC(epp_set_reg)) {
> > > +             if (pcc_ss_id < 0)
> > > +                     return -ENODEV;
> > > +
> > > +             ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
> > > +             if (ret)
> > > +                     return ret;
> > > +
> > > +             pcc_ss_data = pcc_data[pcc_ss_id];
> > > +
> > > +             down_write(&pcc_ss_data->pcc_lock);
> > > +             /* after writing CPC, transfer the ownership of PCC to platform */
> > > +             ret = send_pcc_cmd(pcc_ss_id, CMD_WRITE);
> > > +             up_write(&pcc_ss_data->pcc_lock);
> >
> > cppc_set_auto_epp and cppc_set_epp_perf have nearly the same code in
> > the if block.  I wonder if it's worth having a static helper function
> > for this purpose that takes "reg" and "value" as arguments?
> >
> > > +     }
> 
> And what about the non-PCC case here?

I merge the  cppc_set_auto_epp and cppc_set_epp_perf in V4. 
For the non-PCC case, we canno set the EPP value to FW, then just returned 
Error code.  Is it Ok ?


> 
> > > +
> > > +     return ret;
> > > +}
> > > +EXPORT_SYMBOL_GPL(cppc_set_epp_perf);
> > > +
> > >   /**
> > >    * cppc_set_enable - Set to enable CPPC on the processor by writing the
> > >    * Continuous Performance Control package EnableRegister field.
> > > diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> > > index c5614444031f..10d91aeedaca 100644
> > > --- a/include/acpi/cppc_acpi.h
> > > +++ b/include/acpi/cppc_acpi.h
> > > @@ -108,12 +108,14 @@ struct cppc_perf_caps {
> > >       u32 lowest_nonlinear_perf;
> > >       u32 lowest_freq;
> > >       u32 nominal_freq;
> > > +     u32 energy_perf;
> > >   };
> > >
> > >   struct cppc_perf_ctrls {
> > >       u32 max_perf;
> > >       u32 min_perf;
> > >       u32 desired_perf;
> > > +     u32 energy_perf;
> > >   };
> > >
> > >   struct cppc_perf_fb_ctrs {
> > > @@ -149,6 +151,9 @@ extern bool cpc_ffh_supported(void);
> > >   extern bool cpc_supported_by_cpu(void);
> > >   extern int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val);
> > >   extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64
> > > val);
> > > +extern int cppc_set_auto_epp(int cpu, bool enable); extern int
> > > +cppc_get_epp_caps(int cpunum, struct cppc_perf_caps *perf_caps);
> > > +extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls
> > > +*perf_ctrls);
> > >   #else /* !CONFIG_ACPI_CPPC_LIB */
> > >   static inline int cppc_get_desired_perf(int cpunum, u64 *desired_perf)
> > >   {
> > > @@ -202,6 +207,18 @@ static inline int cpc_write_ffh(int cpunum, struct
> cpc_reg *reg, u64 val)
> > >   {
> > >       return -ENOTSUPP;
> > >   }
> > > +static inline int cppc_set_auto_epp(int cpu, bool enable) {
> > > +     return -ENOTSUPP;
> > > +}
> > > +static inline int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls
> > > +*perf_ctrls) {
> > > +     return -ENOTSUPP;
> > > +}
> > > +static inline int cppc_get_epp_caps(int cpunum, struct
> > > +cppc_perf_caps *perf_caps) {
> > > +     return -ENOTSUPP;
> > > +}
> > >   #endif /* !CONFIG_ACPI_CPPC_LIB */
> > >
> > >   #endif /* _CPPC_ACPI_H*/
> >