linux-kernel - Re: [PATCH] PM / OPP: discard duplicate OPP additions

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Message-ID: <CAGo_u6qTZ-yq26+K5nHut92d=-9nrCHKDNK9EMLK5kGMQc+dOw@mail.gmail.com>
Date:	Tue, 13 May 2014 08:23:03 -0500
From:	Nishanth Menon <nm@...com>
To:	"[Chander Kashyap" <chander.kashyap@...aro.org>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>, pavel@....cz,
	Len Brown <len.brown@...el.com>, gregkh@...uxfoundation.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Chander Kashyap <k.chander@...sung.com>,
	Inderpal Singh <inderpal.s@...sung.com>
Subject: Re: [PATCH] PM / OPP: discard duplicate OPP additions

On Tue, May 13, 2014 at 2:41 AM, [Chander Kashyap
<chander.kashyap@...aro.org> wrote:
> From: Chander Kashyap <k.chander@...sung.com>
>
> It may be possible to unregister and re-register the cpufreq driver.
> One such example is arm big-little IKS cpufreq driver. While
> re-registering the driver, same OPPs may get added again.
>
> This patch detects the duplicacy and discards them.

Nice catch. Thanks for the same.

That said, instead of ignoring it (skipping addition), should we do
the following:
a) if we find the same OPP being added, return error
b) add a cleanup routine dev_pm_opp_remove ?

Original design required OPP entries added by platform code and used
by driver code, but things have changed over time.

>
> Signed-off-by: Chander Kashyap <k.chander@...sung.com>
> Signed-off-by: Inderpal Singh <inderpal.s@...sung.com>
> ---
>  drivers/base/power/opp.c |   28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index 2553867..2e803a9 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -443,23 +443,33 @@ int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
>         new_opp->u_volt = u_volt;
>         new_opp->available = true;
>
> -       /* Insert new OPP in order of increasing frequency */
> +       /*
> +        * Insert new OPP in order of increasing frequency
> +        * and discard if already present
> +        */
>         head = &dev_opp->opp_list;
>         list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
> -               if (new_opp->rate < opp->rate)
> +               if (new_opp->rate <= opp->rate)
>                         break;
>                 else
>                         head = &opp->node;
>         }
>

say we do at this point:
if (new_opp->rate == opp->rate) {
  dev_err(dev, "%s: attempt to add duplicate OPP entry (rate=%ld)\n",
__func__, new_opp->rate)
   kfree(new_opp);
    return -EINVAL;
}
we could avoid the change below, right?

> -       list_add_rcu(&new_opp->node, head);
> -       mutex_unlock(&dev_opp_list_lock);
> +       if (new_opp->rate != opp->rate) {
> +               list_add_rcu(&new_opp->node, head);
> +               mutex_unlock(&dev_opp_list_lock);
> +
> +               /*
> +                * Notify the changes in the availability of the operable
> +                * frequency/voltage list.
> +                */
> +               srcu_notifier_call_chain(&dev_opp->head,
> +                                               OPP_EVENT_ADD, new_opp);
> +       } else {
> +               mutex_unlock(&dev_opp_list_lock);
> +               kfree(new_opp);
> +       }
>
> -       /*
> -        * Notify the changes in the availability of the operable
> -        * frequency/voltage list.
> -        */
> -       srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ADD, new_opp);
>         return 0;
>  }
>  EXPORT_SYMBOL_GPL(dev_pm_opp_add);
> --
> 1.7.9.5
>
> --
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