[PATCH v4] PM / devfreq: Restart previous governor if new governor fails to start

From: Sibi Sankar
Date: Wed Dec 12 2018 - 08:53:31 EST


From: Saravana Kannan <skannan@xxxxxxxxxxxxxx>

If the new governor fails to start, switch back to old governor so that the
devfreq state is not left in some weird limbo.

Signed-off-by: Sibi Sankar <sibis@xxxxxxxxxxxxxx>
Signed-off-by: Saravana Kannan <skannan@xxxxxxxxxxxxxx>
Reviewed-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
---

V4:
* Removed prev_governor check.

V3:
* Fix NULL deref for real this time.
* Addressed some style preferences.

V2:
* Fixed typo in commit text
* Fixed potential NULL deref

drivers/devfreq/devfreq.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 141413067b5c..ba2875a0b90e 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -1024,7 +1024,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
struct devfreq *df = to_devfreq(dev);
int ret;
char str_governor[DEVFREQ_NAME_LEN + 1];
- struct devfreq_governor *governor;
+ const struct devfreq_governor *governor, *prev_governor;

ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
if (ret != 1)
@@ -1053,12 +1053,19 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
goto out;
}
}
+ prev_governor = df->governor;
df->governor = governor;
strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
- if (ret)
+ if (ret) {
dev_warn(dev, "%s: Governor %s not started(%d)\n",
__func__, df->governor->name, ret);
+ df->governor = prev_governor;
+ strncpy(df->governor_name, prev_governor->name,
+ DEVFREQ_NAME_LEN);
+ df->governor->event_handler(df, DEVFREQ_GOV_START,
+ NULL);
+ }
out:
mutex_unlock(&devfreq_list_lock);

--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project