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Subject[RESEND PATCH v5] PM / devfreq: Fix devfreq_add_device() when drivers are built as modules.
Date
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>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.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 4c49bb1330b5..62ead442a872 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)
{
@@ -646,9 +690,8 @@ 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__);
@@ -664,12 +707,14 @@ 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);
@@ -991,7 +1036,7 @@ 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;
--
2.18.0
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