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

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Date:   Sun, 17 Jun 2018 12:50:30 +0900
From:   Chanwoo Choi <cwchoi00@...il.com>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     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 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().

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