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.balle...@collabora.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.balle...@collabora.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
