linux-kernel - Re: [PATCH 03/19] ACPI: CPPC: add cppc enable register function

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Date:   Thu, 9 Sep 2021 17:58:13 +0800
From:   Huang Rui <ray.huang@....com>
To:     Shuah Khan <skhan@...uxfoundation.org>
CC:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...nel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "Sharma, Deepak" <Deepak.Sharma@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        "Fontenot, Nathan" <Nathan.Fontenot@....com>,
        "Su, Jinzhou (Joe)" <Jinzhou.Su@....com>,
        "Du, Xiaojian" <Xiaojian.Du@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 03/19] ACPI: CPPC: add cppc enable register function

On Thu, Sep 09, 2021 at 08:21:48AM +0800, Shuah Khan wrote:
> On 9/8/21 8:59 AM, Huang Rui wrote:
> > From: Jinzhou Su <Jinzhou.Su@....com>
> > 
> > Export the cppc enable register function for future use.
> 
> This patch also adds a new function. How about saying something about
> adding a new function.
> 
> > 
> > Signed-off-by: Jinzhou Su <Jinzhou.Su@....com>
> > Signed-off-by: Huang Rui <ray.huang@....com>
> > ---
> >   drivers/acpi/cppc_acpi.c | 42 ++++++++++++++++++++++++++++++++++++++++
> >   include/acpi/cppc_acpi.h |  5 +++++
> >   2 files changed, 47 insertions(+)
> > 
> > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> > index a4d4eebba1da..de4b30545215 100644
> > --- a/drivers/acpi/cppc_acpi.c
> > +++ b/drivers/acpi/cppc_acpi.c
> > @@ -1220,6 +1220,48 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
> >   }
> >   EXPORT_SYMBOL_GPL(cppc_get_perf_ctrs);
> >   
> > +/**
> > + * cppc_set_enable - Set to enable CPPC register.
> 
> Please make this more descriptive - does it write to register
> What is the behavior in error paths etc.
> 
> > + * @cpu: CPU for which to enable CPPC register.
> > + * @enable: enable field to write into share memory.
> 
> What should this be? What are the valid values to write?
> Also aren't we adding this to header file where prtotype
> is defined these days?

Thank you for the suggestions, I will refine the comments and commmit log
in V2.

> 
> > + *
> > + * Return: 0 for success, -ERRNO otherwise.
> > + */
> > +int cppc_set_enable(int cpu, u32 enable)
> > +{
> > +	int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
> > +	struct cpc_register_resource *enable_reg;
> > +	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> > +	struct cppc_pcc_data *pcc_ss_data = NULL;
> > +	int ret = -1;
> > +
> > +	if (!cpc_desc) {
> > +		pr_debug("No CPC descriptor for CPU:%d\n", cpu);
> > +		return -ENODEV;
> > +	}
> > +
> 
> Don't we need to do some error checking on input args? What is the
> valid range for cpu and enbale?

Good point.

> 
> > +	enable_reg = &cpc_desc->cpc_regs[ENABLE];
> > +
> > +	if (CPC_IN_PCC(enable_reg)) {
> > +
> > +		if (pcc_ss_id < 0)
> > +			return -EIO;
> > +
> > +		ret = cpc_write(cpu, enable_reg, enable);
> > +		if (ret)
> > +			return ret;
> > +
> > +		pcc_ss_data = pcc_data[pcc_ss_id];
> > +
> > +		down_write(&pcc_ss_data->pcc_lock);
> > +		send_pcc_cmd(pcc_ss_id, CMD_WRITE);
> 
> Could this fail?

Will add error handling in V2.

Thanks,
Ray