Re: [PATCH v4 1/3] amd_pstate: Add ->fast_switch() callback

[Rafael J. Wysocki]

On Wed, May 17, 2023 at 6:29 PM Wyes Karny <wyes.karny@xxxxxxx> wrote:
>
> From: "Gautham R. Shenoy" <gautham.shenoy@xxxxxxx>
>
> Schedutil normally calls the adjust_perf callback for drivers with
> adjust_perf callback available and fast_switch_possible flag set.
> However, when frequency invariance is disabled and schedutil tries to
> invoke fast_switch. So, there is a chance of kernel crash if this
> function pointer is not set. To protect against this scenario add
> fast_switch callback to amd_pstate driver.
>
> Fixes: 1d215f0319c2 ("cpufreq: amd-pstate: Add fast switch function for AMD P-State")
>
> Signed-off-by: Wyes Karny <wyes.karny@xxxxxxx>
> Signed-off-by: Gautham R. Shenoy <gautham.shenoy@xxxxxxx>
> ---
>  drivers/cpufreq/amd-pstate.c | 36 ++++++++++++++++++++++++++++++------
>  1 file changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 5a3d4aa0f45a..45711fc0a856 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -444,9 +444,8 @@ static int amd_pstate_verify(struct cpufreq_policy_data *policy)
>         return 0;
>  }
>
> -static int amd_pstate_target(struct cpufreq_policy *policy,
> -                            unsigned int target_freq,
> -                            unsigned int relation)
> +static int amd_pstate_update_freq(struct cpufreq_policy *policy,
> +                                 unsigned int target_freq, bool fast_switch)
>  {
>         struct cpufreq_freqs freqs;
>         struct amd_cpudata *cpudata = policy->driver_data;
> @@ -465,14 +464,37 @@ static int amd_pstate_target(struct cpufreq_policy *policy,
>         des_perf = DIV_ROUND_CLOSEST(target_freq * cap_perf,
>                                      cpudata->max_freq);
>
> -       cpufreq_freq_transition_begin(policy, &freqs);
> +       WARN_ON(fast_switch && !policy->fast_switch_enabled);
> +       /*
> +        * If fast_switch is desired, then there aren't any registered
> +        * transition notifiers. See comment for
> +        * cpufreq_enable_fast_switch().
> +        */
> +       if (!fast_switch)
> +               cpufreq_freq_transition_begin(policy, &freqs);
> +
>         amd_pstate_update(cpudata, min_perf, des_perf,
> -                         max_perf, false, policy->governor->flags);
> -       cpufreq_freq_transition_end(policy, &freqs, false);
> +                       max_perf, fast_switch, policy->governor->flags);
> +
> +       if (!fast_switch)
> +               cpufreq_freq_transition_end(policy, &freqs, false);
>
>         return 0;
>  }
>
> +static int amd_pstate_target(struct cpufreq_policy *policy,
> +                            unsigned int target_freq,
> +                            unsigned int relation)
> +{
> +       return amd_pstate_update_freq(policy, target_freq, false);
> +}
> +
> +static unsigned int amd_pstate_fast_switch(struct cpufreq_policy *policy,
> +                                 unsigned int target_freq)
> +{
> +       return amd_pstate_update_freq(policy, target_freq, true);
> +}
> +
>  static void amd_pstate_adjust_perf(unsigned int cpu,
>                                    unsigned long _min_perf,
>                                    unsigned long target_perf,
> @@ -715,6 +737,7 @@ static int amd_pstate_cpu_exit(struct cpufreq_policy *policy)
>
>         freq_qos_remove_request(&cpudata->req[1]);
>         freq_qos_remove_request(&cpudata->req[0]);
> +       policy->fast_switch_possible = false;
>         kfree(cpudata);
>
>         return 0;
> @@ -1309,6 +1332,7 @@ static struct cpufreq_driver amd_pstate_driver = {
>         .flags          = CPUFREQ_CONST_LOOPS | CPUFREQ_NEED_UPDATE_LIMITS,
>         .verify         = amd_pstate_verify,
>         .target         = amd_pstate_target,
> +       .fast_switch    = amd_pstate_fast_switch,
>         .init           = amd_pstate_cpu_init,
>         .exit           = amd_pstate_cpu_exit,
>         .suspend        = amd_pstate_cpu_suspend,
> --

Applied along with the [2/3], thanks!

Do you need them in 6.4 or would 6.5 be sufficient?  Also do you need
them to go into "stable"?