linux-kernel - Re: [PATCH] cpufreq-dt: defer probing if OPP table is not ready

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Message-ID: <CAKohpo=mcG99N5q_CCua8Hdydo=ydHKD-CiTJO9SsAhLvkTJHw@mail.gmail.com>
Date:	Tue, 16 Dec 2014 10:40:27 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Dmitry Torokhov <dtor@...omium.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Lucas Stach <l.stach@...gutronix.de>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Stefan Wahren <stefan.wahren@...e.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq-dt: defer probing if OPP table is not ready

On 16 December 2014 at 05:40, Dmitry Torokhov <dtor@...omium.org> wrote:
> cpufreq-dt driver supports mode when OPP table is provided by platform
> code and not device tree. However on certain platforms code that fills
> OPP table may run after cpufreq driver tries to initialize, so let's
> report -EPROBE_DEFER if we do not find any entires in OPP table for the
> CPU.
>
> Signed-off-by: Dmitry Torokhov <dtor@...omium.org>
> ---
>  drivers/cpufreq/cpufreq-dt.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
> index f56147a..4f874fa 100644
> --- a/drivers/cpufreq/cpufreq-dt.c
> +++ b/drivers/cpufreq/cpufreq-dt.c
> @@ -211,6 +211,19 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>         /* OPPs might be populated at runtime, don't check for error here */
>         of_init_opp_table(cpu_dev);
>
> +       /*
> +        * But we need OPP table to function so if it is not there let's
> +        * give platform code chance to provide it for us.
> +        */
> +       rcu_read_lock();
> +       ret = dev_pm_opp_get_opp_count(cpu_dev);
> +       rcu_read_unlock();
> +       if (ret <= 0) {
> +               pr_debug("OPP table is not ready, deferring probe\n");
> +               ret = -EPROBE_DEFER;
> +               goto out_free_opp;

Hmm, so we are trying to free opps while we failed to find one.

Are you sure you have tested this on one such platform where we
fail here?

Because this is what I see:

void of_free_opp_table(struct device *dev)
{
        struct device_opp *dev_opp;
        struct dev_pm_opp *opp, *tmp;

        /* Check for existing list for 'dev' */
        dev_opp = find_device_opp(dev);
        if (WARN(IS_ERR(dev_opp), "%s: dev_opp: %ld\n", dev_name(dev),
                 PTR_ERR(dev_opp)))
                return;

        ...
}


And we probably will hit this WARN(), wouldn't we ?

> +       }
> +
>         priv = kzalloc(sizeof(*priv), GFP_KERNEL);
>         if (!priv) {
>                 ret = -ENOMEM;
> --
> 2.2.0.rc0.207.ga3a616c
>
>
> --
> Dmitry
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