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Subject[PATCH v6 1/3] PM / devfreq: Fix handling of min/max_freq == 0
Date
Commit ab8f58ad72c4 ("PM / devfreq: Set min/max_freq when adding the
devfreq device") initializes df->min/max_freq with the min/max OPP when
the device is added. Later commit f1d981eaecf8 ("PM / devfreq: Use the
available min/max frequency") adds df->scaling_min/max_freq and the
following to the frequency adjustment code:

max_freq = MIN(devfreq->scaling_max_freq, devfreq->max_freq);

With the current handling of min/max_freq this is incorrect:

Even though df->max_freq is now initialized to a value != 0 user space
can still set it to 0, in this case max_freq would be 0 instead of
df->scaling_max_freq as intended. In consequence the frequency adjustment
is not performed:

if (max_freq && freq > max_freq) {
freq = max_freq;

To fix this set df->min/max freq to the min/max OPP in max/max_freq_store,
when the user passes a value of 0. This also prevents df->max_freq from
being set below the min OPP when df->min_freq is 0, and similar for
min_freq. Since it is now guaranteed that df->min/max_freq can't be 0 the
checks for this case can be removed.

Fixes: f1d981eaecf8 ("PM / devfreq: Use the available min/max frequency")
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
---
Changes in v6:
- min/max_freq_store(): updated comment about sorting order of
frequency table
- min/max_freq_store(): moved declaration of 'freq_table' into the
block that uses it
- added 'Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>' tag

Changes in v5:
- none

Changes in v4:
- added 'Reviewed-by: Brian Norris <briannorris@chromium.org>' tag

Changes in v3:
- none

Changes in v2:
- handle freq tables sorted in ascending and descending order in
min/max_freq_store()
- use same order for conditional statements in min/max_freq_store()
---
drivers/devfreq/devfreq.c | 42 ++++++++++++++++++++++++++++-----------
1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 4c49bb1330b5..772e8aab1627 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -283,11 +283,11 @@ int update_devfreq(struct devfreq *devfreq)
max_freq = MIN(devfreq->scaling_max_freq, devfreq->max_freq);
min_freq = MAX(devfreq->scaling_min_freq, devfreq->min_freq);

- if (min_freq && freq < min_freq) {
+ if (freq < min_freq) {
freq = min_freq;
flags &= ~DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use GLB */
}
- if (max_freq && freq > max_freq) {
+ if (freq > max_freq) {
freq = max_freq;
flags |= DEVFREQ_FLAG_LEAST_UPPER_BOUND; /* Use LUB */
}
@@ -1126,17 +1126,26 @@ static ssize_t min_freq_store(struct device *dev, struct device_attribute *attr,
struct devfreq *df = to_devfreq(dev);
unsigned long value;
int ret;
- unsigned long max;

ret = sscanf(buf, "%lu", &value);
if (ret != 1)
return -EINVAL;

mutex_lock(&df->lock);
- max = df->max_freq;
- if (value && max && value > max) {
- ret = -EINVAL;
- goto unlock;
+
+ if (value) {
+ if (value > df->max_freq) {
+ ret = -EINVAL;
+ goto unlock;
+ }
+ } else {
+ unsigned long *freq_table = df->profile->freq_table;
+
+ /* Get minimum frequency according to sorting order */
+ if (freq_table[0] < freq_table[df->profile->max_state - 1])
+ value = freq_table[0];
+ else
+ value = freq_table[df->profile->max_state - 1];
}

df->min_freq = value;
@@ -1161,17 +1170,26 @@ static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
struct devfreq *df = to_devfreq(dev);
unsigned long value;
int ret;
- unsigned long min;

ret = sscanf(buf, "%lu", &value);
if (ret != 1)
return -EINVAL;

mutex_lock(&df->lock);
- min = df->min_freq;
- if (value && min && value < min) {
- ret = -EINVAL;
- goto unlock;
+
+ if (value) {
+ if (value < df->min_freq) {
+ ret = -EINVAL;
+ goto unlock;
+ }
+ } else {
+ unsigned long *freq_table = df->profile->freq_table;
+
+ /* Get maximum frequency according to sorting order */
+ if (freq_table[0] < freq_table[df->profile->max_state - 1])
+ value = freq_table[df->profile->max_state - 1];
+ else
+ value = freq_table[0];
}

df->max_freq = value;
--
2.18.0.597.ga71716f1ad-goog
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