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

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Date:   Thu, 14 Feb 2019 11:58:51 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.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 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.

> +
>         ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0);
>         if (ret)
>                 return ret;
> @@ -357,6 +370,61 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
>         .name = "cppc_cpufreq",
>  };
>
> +/*
> + * HISI platform does not support delivered performance counter and
> + * reference performance counter. It can calculate the performance using the
> + * platform specific mechanism. We reuse the desired performance register to
> + * store the real performance calculated by the platform.
> + */
> +static unsigned int hisi_cppc_cpufreq_get_rate(unsigned int cpunum)
> +{
> +       struct cppc_cpudata *cpudata = all_cpu_data[cpunum];
> +       u64 desired_perf;
> +       int ret;
> +
> +       ret = cppc_get_desired_perf(cpunum, &desired_perf);
> +       if (ret < 0)
> +               return -EIO;
> +
> +       return cppc_cpufreq_perf_to_khz(cpudata, desired_perf);
> +}
> +
> +static struct cppc_workaround_info wa_info[] = {
> +       {
> +               .oem_id         = "HISI  ",
> +               .oem_table_id   = "HIP07   ",
> +               .oem_revision   = 0,
> +               .get_rate = hisi_cppc_cpufreq_get_rate,
> +       }, {
> +               .oem_id         = "HISI  ",
> +               .oem_table_id   = "HIP08   ",
> +               .oem_revision   = 0,
> +               .get_rate = hisi_cppc_cpufreq_get_rate,
> +       }
> +};
> +
> +static int cppc_check_workaround(void)

And this function can be a void one.


> +{
> +       struct acpi_table_header *tbl;
> +       acpi_status status = AE_OK;
> +       int i;
> +
> +       status = acpi_get_table(ACPI_SIG_PCCT, 0, &tbl);
> +       if (ACPI_FAILURE(status) || !tbl)
> +               return -EINVAL;
> +
> +       for (i = 0; i < ARRAY_SIZE(wa_info); i++) {
> +               if (!memcmp(wa_info[i].oem_id, tbl->oem_id, ACPI_OEM_ID_SIZE) &&
> +                   !memcmp(wa_info[i].oem_table_id, tbl->oem_table_id, ACPI_OEM_TABLE_ID_SIZE) &&
> +                   wa_info[i].oem_revision == tbl->oem_revision) {
> +                       cppc_wa_get_rate = wa_info[i].get_rate;
> +                       return 0;
> +               }
> +       }
> +
> +       return -ENODEV;
> +}
> +
>  static int __init cppc_cpufreq_init(void)
>  {
>         int i, ret = 0;
> @@ -386,6 +454,8 @@ static int __init cppc_cpufreq_init(void)
>                 goto out;
>         }
>
> +       cppc_check_workaround();
> +
>         ret = cpufreq_register_driver(&cppc_cpufreq_driver);
>         if (ret)
>                 goto out;
> --