linux-kernel - Re: [PATCH 2/3] cpufreq, powernow-k6: Fix double invocation of cpufreq_freq_transition

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Date:	Fri, 25 Apr 2014 13:58:27 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Meelis Roos <mroos@...ux.ee>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] cpufreq, powernow-k6: Fix double invocation of cpufreq_freq_transition_begin/end

On 25 April 2014 13:48, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> During frequency transitions, the cpufreq core takes the responsibility of
> invoking cpufreq_freq_transition_begin() and cpufreq_freq_transition_end()
> for those cpufreq drivers that define the ->target_index callback but don't
> set the ASYNC_NOTIFICATION flag.
>
> The powernow-k6 cpufreq driver falls under this category, but this driver was
> invoking the _begin() and _end() APIs itself around frequency transitions,
> which led to double invocation of the _begin() API. The _begin API makes
> contending callers wait until the previous invocation is complete. Hence,
> the powernow-k6 driver ended up waiting on itself, leading to system hangs
> during boot.
>
> Fix this by removing the calls to the _begin() and _end() APIs from the
> powernow-k6 driver, since they rightly belong to the cpufreq core.
>
> (Note that during ->exit(), the powernow-k6 driver sets the frequency
>  without any help from the cpufreq core. So add explicit calls to the
>  _begin() and _end() APIs around that frequency transition alone, to take
>  care of that special case. Also, add a missing 'break' statement there.)
>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> ---
>
>  drivers/cpufreq/powernow-k6.c |   20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/cpufreq/powernow-k6.c b/drivers/cpufreq/powernow-k6.c
> index 49f120e..6a4c34e 100644
> --- a/drivers/cpufreq/powernow-k6.c
> +++ b/drivers/cpufreq/powernow-k6.c
> @@ -138,22 +138,14 @@ static void powernow_k6_set_cpu_multiplier(unsigned int best_i)
>  static int powernow_k6_target(struct cpufreq_policy *policy,
>                 unsigned int best_i)
>  {
> -       struct cpufreq_freqs freqs;
>
>         if (clock_ratio[best_i].driver_data > max_multiplier) {
>                 printk(KERN_ERR PFX "invalid target frequency\n");
>                 return -EINVAL;
>         }
>
> -       freqs.old = busfreq * powernow_k6_get_cpu_multiplier();
> -       freqs.new = busfreq * clock_ratio[best_i].driver_data;
> -
> -       cpufreq_freq_transition_begin(policy, &freqs);
> -
>         powernow_k6_set_cpu_multiplier(best_i);
>
> -       cpufreq_freq_transition_end(policy, &freqs, 0);
> -
>         return 0;
>  }
>
> @@ -228,8 +220,18 @@ static int powernow_k6_cpu_exit(struct cpufreq_policy *policy)
>  {
>         unsigned int i;
>         for (i = 0; i < 8; i++) {
> -               if (i == max_multiplier)
> +               if (i == max_multiplier) {

This wouldn't work, it has to be: (clock_ratio[i].driver_data == max_multiplier)

> +                       struct cpufreq_freqs freqs;
> +
> +                       freqs.old = policy->cur;
> +                       freqs.new = clock_ratio[i].frequency;
> +                       freqs.flags = 0;
> +
> +                       cpufreq_freq_transition_begin(policy, &freqs);
>                         powernow_k6_target(policy, i);
> +                       cpufreq_freq_transition_end(policy, &freqs, 0);
> +                       break;
> +               }
>         }
>         return 0;
>  }

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
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