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@collabora.com ---

Changes in v5: - Requested by MyungJoo and Chanwoo. - Fix returning without the lock acquired after request_module. - Requested by Chanwoo. - In request governor function check if governor name is NULL or not. - Remove some unrelated changes (added/removed some blank lines).

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, 49 insertions(+), 4 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c index 0b5b3abe054e..aa92fbf9f0dd 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 +222,49 @@ 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 + * + * 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. Returns the matched + * governor's pointer. + */ +static struct devfreq_governor *try_then_request_governor(const char *name) +{ + struct devfreq_governor *governor; + int err = 0; + + 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); + /* Restore previous state before return */ + mutex_lock(&devfreq_list_lock); + if (err) + return NULL; + + governor = find_devfreq_governor(name); + } + + return governor; +} + static int devfreq_notify_transition(struct devfreq *devfreq, struct devfreq_freqs *freqs, unsigned int state) { @@ -645,9 +689,8 @@ struct devfreq *devfreq_add_device(struct device *dev, mutex_unlock(&devfreq->lock);

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__); @@ -663,12 +706,14 @@ 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);

device_unregister(&devfreq->dev); @@ -989,7 +1034,7 @@ 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); + governor = try_then_request_governor(str_governor); if (IS_ERR(governor)) { ret = PTR_ERR(governor); goto out;