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    Subject[PATCH 4.19 042/220] PM / devfreq: Fix handling of min/max_freq == 0
    Date
    From: Matthias Kaehlcke <mka@chromium.org>

    [ Upstream commit df5cf4a36178c5d4f2b8b9469cb2f722e64cd102 ]

    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>
    Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 62ead442a8721..8e21bedc74c38 100644
    --- a/drivers/devfreq/devfreq.c
    +++ b/drivers/devfreq/devfreq.c
    @@ -327,11 +327,11 @@ 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 */
    }
    @@ -1171,17 +1171,26 @@ 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;
    @@ -1206,17 +1215,26 @@ 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;
    --
    2.20.1


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