linux-kernel - Re: [PATCH v2 2/2] cpufreq / cppc: Work around for Hisilicon CPPC cpufreq

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Message-ID: <2813657.1l3PCoQO4Z@aspire.rjw.lan>
Date:   Fri, 15 Feb 2019 00:15:52 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>, gcherianv@...il.com,
        Prashanth Prakash <pprakash@...eaurora.org>,
        George Cherian <george.cherian@...ium.com>,
        Robert Moore <robert.moore@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        John Garry <john.garry@...wei.com>
Subject: Re: [PATCH v2 2/2] cpufreq / cppc: Work around for Hisilicon CPPC cpufreq

On Thursday, February 14, 2019 2:58:21 PM CET Xiongfeng Wang wrote:
> 
> On 2019/2/14 18:58, Rafael J. Wysocki wrote:
> > On Thu, Feb 14, 2019 at 8:46 AM Xiongfeng Wang
> > <wangxiongfeng2@...wei.com> wrote:
> >>
> >> Hisilicon chips do not support delivered performance counter register
> >> and reference performance counter register. But the platform can
> >> calculate the real performance using its own method. This patch provide
> >> a workaround for this problem, and other platforms can also use this
> >> workaround framework. We reuse the desired performance register to
> >> store the real performance calculated by the platform. After the
> >> platform finished the frequency adjust, it gets the real performance and
> >> writes it into desired performance register. OS can use it to calculate
> >> the real frequency.
> >>
> >> Signed-off-by: Xiongfeng Wang <wangxiongfeng2@...wei.com>
> >> ---
> >>  drivers/cpufreq/cppc_cpufreq.c | 70 ++++++++++++++++++++++++++++++++++++++++++
> >>  1 file changed, 70 insertions(+)
> >>
> >> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> >> index fd25c21c..da96fec 100644
> >> --- a/drivers/cpufreq/cppc_cpufreq.c
> >> +++ b/drivers/cpufreq/cppc_cpufreq.c
> >> @@ -33,6 +33,16 @@
> >>  /* Offest in the DMI processor structure for the max frequency */
> >>  #define DMI_PROCESSOR_MAX_SPEED  0x14
> >>
> >> +struct cppc_workaround_info {
> >> +       char oem_id[ACPI_OEM_ID_SIZE +1];
> >> +       char oem_table_id[ACPI_OEM_TABLE_ID_SIZE + 1];
> >> +       u32 oem_revision;
> >> +       unsigned int (*get_rate)(unsigned int cpu);
> >> +};
> >> +
> >> +/* CPPC workaround for get_rate callback */
> >> +unsigned int (*cppc_wa_get_rate)(unsigned int cpu);
> >> +
> > 
> > First off, please don't split the workaround material into two parts.
> > IOW, the other new function added below can go here just fine IMO.
> > 
> >>  /*
> >>   * These structs contain information parsed from per CPU
> >>   * ACPI _CPC structures.
> >> @@ -334,6 +344,9 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
> >>         struct cppc_cpudata *cpu = all_cpu_data[cpunum];
> >>         int ret;
> >>
> >> +       if (cppc_wa_get_rate)
> >> +               return cppc_wa_get_rate(cpunum);
> > 
> > Second, what is the value of using the function pointer above?
> > 
> > All we need for now is a flag to indicate whether or not to call
> > hisi_cppc_cpufreq_get_rate() here and return its return value.
> 
> How about adding a pointer of 'struct cppc_workaround_info' to indicate whether we have
> found a matches workaround ?
> If I use a flag, I will need another variable to indicate which item of the workaround array 'wa_info'
> to use.

And why do you need to distinguish one of them from the other?