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Date: Wed, 04 Jul 2018 10:06:46 +0900
From: Chanwoo Choi <cw00.choi@...sung.com>
To: Enric Balletbo i Serra <enric.balletbo@...labora.com>,
linux-kernel@...r.kernel.org
Cc: kernel@...labora.com, Kyungmin Park <kyungmin.park@...sung.com>,
MyungJoo Ham <myungjoo.ham@...sung.com>,
linux-pm@...r.kernel.org
Subject: Re: [PATCH v4] PM / devfreq: Fix devfreq_add_device() when drivers
are built as modules.
Hi Enric,
On 2018년 07월 03일 22:29, Enric Balletbo i Serra wrote:
> When the devfreq driver and the governor driver are built as modules,
> the call to devfreq_add_device() or governor_store() 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 by adding a try_then_request_governor()
> function. First tries to find the governor, and then, if it is 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>
> ---
>
> Changes in v4:
> - Kept "locked" devfreq_list from the return of find_devfreq_governor() to
> the unlock of governor_store(). Requested by MyungJoo Ham.
>
> Changes in v3:
> - Remove unneded change in dev_err message.
> - Fix err returned value in case to not find the governor.
>
> Changes in v2:
> - Add a new function to request the module and call that function from
> devfreq_add_device and governor_store.
>
> drivers/devfreq/devfreq.c | 53 ++++++++++++++++++++++++++++++++++-----
> 1 file changed, 47 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 0b5b3abe054e..4ea6b19879a1 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>
> @@ -221,6 +222,46 @@ static struct devfreq_governor *find_devfreq_governor(const char *name)
> return ERR_PTR(-ENODEV);
> }
>
> +/**
> + * try_then_request_governor() - Try to find the governor and request the
> + * module if is not found.
> + * @name: name of the governor
Usually, devfreq used 'governor_name' indicating the name of governor.
you better to use 'governor_name' instead of 'name' for more readability.
> + *
> + * Search the list of devfreq governors and request the module and try again
> + * if is not found. This can happen when both drivers (the governor driver
> + * and the driver that call devfreq_add_device) are built as modules.
> + * devfreq_list_lock should be held by the caller.
> + *
> + * Return: The matched governor's pointer.
Usually, devfreq.c didn;t use the 'Return: ...'. So, you better to explain
what is returned from this function with function description.
> + */
> +static struct devfreq_governor *try_then_request_governor(const char *name)
ditto. (name -> governor_name)
> +{
> + struct devfreq_governor *governor;
> + int err = 0;
You have to check whether governor name is NULL or not.
if (IS_ERR_OR_NULL(name)) {
pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
return ERR_PTR(-EINVAL);
}
> +
> + WARN(!mutex_is_locked(&devfreq_list_lock),
> + "devfreq_list_lock must be locked.");
> +
> + governor = find_devfreq_governor(name);
> + if (IS_ERR(governor)) {
> + mutex_unlock(&devfreq_list_lock);
> +
> + if (!strncmp(name, DEVFREQ_GOV_SIMPLE_ONDEMAND,
> + DEVFREQ_NAME_LEN))
> + err = request_module("governor_%s", "simpleondemand");
> + else
> + err = request_module("governor_%s", name);
> + if (err)
> + return NULL;
When error happen, you unlock the mutex. If failed to request module,
you should restore the previous state. Please mutex_lock(&devfreq_list_lock)
before return.
> +
> + mutex_lock(&devfreq_list_lock);
> +
> + governor = find_devfreq_governor(name);
> + }
> +
> + return governor;
> +}
> +
> static int devfreq_notify_transition(struct devfreq *devfreq,
> struct devfreq_freqs *freqs, unsigned int state)
> {
> @@ -643,11 +684,9 @@ struct devfreq *devfreq_add_device(struct device *dev,
> srcu_init_notifier_head(&devfreq->transition_notifier_list);
>
> mutex_unlock(&devfreq->lock);
> -
This change is not related to this patch.
> mutex_lock(&devfreq_list_lock);
> - list_add(&devfreq->node, &devfreq_list);
>
> - governor = find_devfreq_governor(devfreq->governor_name);
> + governor = try_then_request_governor(devfreq->governor_name);
> if (IS_ERR(governor)) {
> dev_err(dev, "%s: Unable to find governor for the device\n",
> __func__);
> @@ -663,14 +702,15 @@ struct devfreq *devfreq_add_device(struct device *dev,
> __func__);
> goto err_init;
> }
> +
> + list_add(&devfreq->node, &devfreq_list);
> +
> mutex_unlock(&devfreq_list_lock);
>
> return devfreq;
>
> err_init:
> - list_del(&devfreq->node);
> mutex_unlock(&devfreq_list_lock);
> -
This change is not related to this patch.
> device_unregister(&devfreq->dev);
> err_dev:
> if (devfreq)
> @@ -989,7 +1029,8 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
> return -EINVAL;
>
> mutex_lock(&devfreq_list_lock);
> - governor = find_devfreq_governor(str_governor);
> +
Don't need to add the blank line. It is enough to change the function
from find_devfreq_governor to try_then_request_governor.
> + governor = try_then_request_governor(str_governor);
> if (IS_ERR(governor)) {
> ret = PTR_ERR(governor);
> goto out;
>
--
Best Regards,
Chanwoo Choi
Samsung Electronics
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