On 6/22/2018 1:52 PM, Enric Balletbo i Serra wrote:
Hi Ezequiel and Akhil,
On 22/06/18 09:03, Akhil P Oommen wrote:
On 6/22/2018 6:41 AM, Ezequiel Garcia wrote:
Hey Enric,
On Fri, 2018-06-22 at 00:04 +0200, 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.balle...@collabora.com>
---
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 | 65 ++++++++++++++++++++++++++++++++-----
--
[snip snip]
- 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__);
err = PTR_ERR(governor);
- goto err_init;
+ goto err_unregister;
}
+ mutex_lock(&devfreq_list_lock);
+
I know it's not something we are introducing in this patch,
but still... calling a hook with a mutex held looks
fishy to me.
This lock should only protect the list, unless I am missing
something.
I think so too.
devfreq->governor = governor;
err = devfreq->governor->event_handler(devfreq,
DEVFREQ_GOV_START,
NULL);
@@ -663,14 +703,16 @@ 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);
-
+err_unregister:
device_unregister(&devfreq->dev);
err_dev:
if (devfreq)
@@ -988,12 +1030,13 @@ static ssize_t governor_store(struct device
*dev, struct device_attribute *attr,
if (ret != 1)
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;
+ return PTR_ERR(governor);
}
+
+ mutex_lock(&devfreq_list_lock);
+
if (df->governor == governor) {
ret = 0;
goto out;
--
2.17.1
Regards,
Eze
Adding to Ezequiel's point, shouldn't we take more granular lock (devfreq->lock)
first and then call devfreq_list_lock at the time of adding to the list?
Yes, I think so. I think, though, that this should be a separate patch, not sure
if a pre or post patch to this one, but for sure it's another topic. Current
patch tries to solve different problem an only tries to follow the current
locking/unlocking. Anyway this is a maintainer decision I guess.
Thanks,
Enric
-Akhil.
I agree.
-Akhil.
