linux-kernel - Re: [PATCH] PM / devfreq: Fix devfreq_add_device() when drivers are built as modules.

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Date:   Mon, 18 Jun 2018 11:02:54 +0200
From:   Enric Balletbo Serra <eballetbo@...il.com>
To:     cwchoi00@...il.com
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        kernel@...labora.com, Chanwoo Choi <cw00.choi@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] PM / devfreq: Fix devfreq_add_device() when drivers are
 built as modules.

Hi Chanwoo,
Missatge de Chanwoo Choi <cwchoi00@...il.com> del dia dg., 17 de juny
2018 a les 5:50:
>
> Hi Enric,
>
> This issue will happen on the position to use find_devfreq_governor()
> as following:
> - devfreq_add_governora() and governor_store()
>
> If device driver with module type after loaded want to change the
> scaling governor,
> new governor might be not yet loaded. So, devfreq bettero to consider this case
> in the find_devfreq_governor().
>
Ok, I'll move there and send a v2.

Thanks
 Enric.


> 2018-06-15 19:04 GMT+09:00 Enric Balletbo i Serra
> <enric.balletbo@...labora.com>:
> > When the devfreq driver and the governor driver are built as modules,
> > the call to devfreq_add_device() fails because the governor driver is
> > not loaded at the time the devfreq driver loads. The devfreq driver has
> > a build dependency on the governor but also should have a runtime
> > dependency. We need to make sure that the governor driver is loaded
> > before the devfreq driver.
> >
> > This patch fixes this bug in devfreq_add_device(). First tries to find
> > the governor, and then, if was not found, it requests the module and
> > tries again.
> >
> > Fixes: 1b5c1be2c88e (PM / devfreq: map devfreq drivers to governor using name)
> > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> > ---
> >
> >  drivers/devfreq/devfreq.c | 36 +++++++++++++++++++++++++++++++-----
> >  1 file changed, 31 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> > index fe2af6aa88fc..1d917f043e30 100644
> > --- a/drivers/devfreq/devfreq.c
> > +++ b/drivers/devfreq/devfreq.c
> > @@ -11,6 +11,7 @@
> >   */
> >
> >  #include <linux/kernel.h>
> > +#include <linux/kmod.h>
> >  #include <linux/sched.h>
> >  #include <linux/errno.h>
> >  #include <linux/err.h>
> > @@ -648,10 +649,35 @@ struct devfreq *devfreq_add_device(struct device *dev,
> >
> >         governor = find_devfreq_governor(devfreq->governor_name);
> >         if (IS_ERR(governor)) {
> > -               dev_err(dev, "%s: Unable to find governor for the device\n",
> > -                       __func__);
> > -               err = PTR_ERR(governor);
> > -               goto err_init;
> > +               list_del(&devfreq->node);
> > +               mutex_unlock(&devfreq_list_lock);
> > +
> > +               /*
> > +                * If the governor is not found, then request the module and
> > +                * try again. This can happen when both drivers (the governor
> > +                * driver and the driver that calls devfreq_add_device) are
> > +                * built as modules.
> > +                */
> > +               if (!strncmp(devfreq->governor_name,
> > +                            DEVFREQ_GOV_SIMPLE_ONDEMAND, DEVFREQ_NAME_LEN))
> > +                       err = request_module("governor_%s", "simpleondemand");
> > +               else
> > +                       err = request_module("governor_%s",
> > +                                            devfreq->governor_name);
> > +               if (err)
> > +                       goto err_unregister;
> > +
> > +               mutex_lock(&devfreq_list_lock);
> > +               list_add(&devfreq->node, &devfreq_list);
> > +
> > +               governor = find_devfreq_governor(devfreq->governor_name);
> > +               if (IS_ERR(governor)) {
> > +                       dev_err(dev,
> > +                               "%s: Unable to find governor for the device\n",
> > +                               __func__);
> > +                       err = PTR_ERR(governor);
> > +                       goto err_init;
> > +               }
> >         }
> >
> >         devfreq->governor = governor;
> > @@ -669,7 +695,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
> >  err_init:
> >         list_del(&devfreq->node);
> >         mutex_unlock(&devfreq_list_lock);
> > -
> > +err_unregister:
> >         device_unregister(&devfreq->dev);
> >  err_dev:
> >         if (devfreq)
> > --
> > 2.17.1
> >
>
>
>
> --
> Best Regards,
> Chanwoo Choi
> Samsung Electronics