[RFC,2/2] PM / devfreq: Use PM QoS for sysfs min/max_freq

Commit Message

Leonard Crestez Nov. 19, 2019, 4:12 p.m. UTC

Switch the handling of min_freq and max_freq from sysfs to use the
dev_pm_qos_request interface.

Since PM QoS handles frequencies as kHz this change reduces the
precision of min_freq and max_freq. This shouldn't introduce problems
because frequencies which are not an integer number of kHz are likely
not an integer number of Hz either.

Try to ensure compatibility by rounding min values down and rounding
max values up.

Signed-off-by: Leonard Crestez <[e-mail]>
---
 drivers/devfreq/devfreq.c | 76 ++++++++++++++++++++++++++++++---------
 include/linux/devfreq.h   |  9 ++---
 2 files changed, 64 insertions(+), 21 deletions(-)

Comments

Matthias Kaehlcke Nov. 21, 2019, 11:16 p.m. UTC | #1

Hi Leonard,

this seems to work ok as long as there are no other ('external') PM QoS
requests, however the aggregate max_freq can be incorrect when there are
multiple requests.

I intended to test with devfreq_cooling using PM QoS, but this didn't work
out due to limitations on my development platform. Instead I added another
set of requests and sysfs attributes to devfreq (see patch below).

With this we get:

cat available_frequencies
  180000000 267000000 355000000 430000000 565000000 650000000 800000000

# ok
cat max_freq
  800000000

# wtf???
echo 650000000 > max_freq
cat max_freq
  800000000

# this looks better
echo 800000000 > test_max_freq
cat max_freq
  650000000


The problem appears to be:

#define PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE      (-1)

in include/linux/pm_qos.h (added by "PM / QoS: Restore
DEV_PM_QOS_MIN/MAX_FREQUENCY")

The aggregate value returned by
dev_pm_qos_read_value(dev, DEV_PM_QOS_MAX_FREQUENCY) is the
smallest of all requests, which is PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE
unless all requests have set an actual constraint.

You probably want to change the constant to resolve to S32_MAX or some
other big value.

Cheers

Matthias


diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 4e6b3c05b3706f..935098bfadf944 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -659,6 +659,18 @@ static void devfreq_dev_release(struct device *dev)
                        dev_warn(dev->parent,
                                "Failed to remove min_freq request: %d\n", err);
        }
+       if (dev_pm_qos_request_active(&devfreq->test_max_freq_req)) {
+               err = dev_pm_qos_remove_request(&devfreq->test_max_freq_req);
+               if (err)
+                       dev_warn(dev->parent,
+                               "Failed to remove test_max_freq request: %d\n", err);
+       }
+       if (dev_pm_qos_request_active(&devfreq->test_min_freq_req)) {
+               err = dev_pm_qos_remove_request(&devfreq->test_min_freq_req);
+               if (err)
+                       dev_warn(dev->parent,
+                               "Failed to remove test_min_freq request: %d\n", err);
+       }

        if (devfreq->profile->exit)
                devfreq->profile->exit(devfreq->dev.parent);
@@ -738,6 +750,16 @@ struct devfreq *devfreq_add_device(struct device *dev,
        if (err < 0)
                goto err_dev;

+       err = dev_pm_qos_add_request(dev, &devfreq->test_min_freq_req,
+                                    DEV_PM_QOS_MIN_FREQUENCY, 0);
+       if (err < 0)
+               goto err_dev;
+       err = dev_pm_qos_add_request(dev, &devfreq->test_max_freq_req,
+                                    DEV_PM_QOS_MAX_FREQUENCY,
+                                    PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE);
+       if (err < 0)
+               goto err_dev;
+
        devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
        devfreq->opp_table = dev_pm_opp_get_opp_table(dev);
        if (IS_ERR(devfreq->opp_table))
@@ -1454,6 +1476,101 @@ static ssize_t max_freq_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RW(max_freq);

+static ssize_t test_min_freq_store(struct device *dev, struct device_attribute *attr,
+                             const char *buf, size_t count)
+{
+       struct devfreq *df = to_devfreq(dev);
+       unsigned long value;
+       int ret;
+
+       /*
+        * Protect against theoretical sysfs writes between
+        * device_add and dev_pm_qos_add_request
+        */
+       if (!dev_pm_qos_request_active(&df->test_min_freq_req))
+               return -EINVAL;
+
+       ret = sscanf(buf, "%lu", &value);
+       if (ret != 1)
+               return -EINVAL;
+
+       /* Round down to kHz for PM QoS */
+       ret = dev_pm_qos_update_request(&df->test_min_freq_req,
+                                       value / HZ_PER_KHZ);
+       if (ret < 0)
+               return ret;
+
+       return count;
+}
+
+static ssize_t test_min_freq_show(struct device *dev, struct device_attribute *attr,
+                            char *buf)
+{
+       struct devfreq *df = to_devfreq(dev);
+       unsigned long min_freq, max_freq;
+
+       mutex_lock(&df->lock);
+       get_freq_range(df, &min_freq, &max_freq);
+       mutex_unlock(&df->lock);
+
+       return sprintf(buf, "%lu\n", min_freq);
+}
+
+static ssize_t test_max_freq_store(struct device *dev, struct device_attribute *attr,
+                             const char *buf, size_t count)
+{
+       struct devfreq *df = to_devfreq(dev);
+       unsigned long value;
+       int ret;
+
+       /*
+        * Protect against theoretical sysfs writes between
+        * device_add and dev_pm_qos_add_request
+        */
+       if (!dev_pm_qos_request_active(&df->test_max_freq_req))
+               return -EINVAL;
+
+       ret = sscanf(buf, "%lu", &value);
+       if (ret != 1)
+               return -EINVAL;
+
+       /*
+        * PM QoS frequencies are in kHz so we need to convert. Convert by
+        * rounding upwards so that the acceptable interval never shrinks.
+        *
+        * For example if the user writes "666666666" to sysfs this value will
+        * be converted to 666667 kHz and back to 666667000 Hz before an OPP
+        * lookup, this ensures that an OPP of 666666666Hz is still accepted.
+        *
+        * A value of zero means "no limit".
+        */
+       if (value)
+               value = DIV_ROUND_UP(value, HZ_PER_KHZ);
+       else
+               value = PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE;
+
+       ret = dev_pm_qos_update_request(&df->test_max_freq_req, value);
+       if (ret < 0)
+               return ret;
+
+       return count;
+}
+static DEVICE_ATTR_RW(test_min_freq);
+
+static ssize_t test_max_freq_show(struct device *dev, struct device_attribute *attr,
+                            char *buf)
+{
+       struct devfreq *df = to_devfreq(dev);
+       unsigned long min_freq, max_freq;
+
+       mutex_lock(&df->lock);
+       get_freq_range(df, &min_freq, &max_freq);
+       mutex_unlock(&df->lock);
+
+       return sprintf(buf, "%lu\n", max_freq);
+}
+static DEVICE_ATTR_RW(test_max_freq);
+
 static ssize_t available_frequencies_show(struct device *d,
                                          struct device_attribute *attr,
                                          char *buf)
@@ -1532,6 +1649,8 @@ static struct attribute *devfreq_attrs[] = {
        &dev_attr_polling_interval.attr,
        &dev_attr_min_freq.attr,
        &dev_attr_max_freq.attr,
+       &dev_attr_test_min_freq.attr,
+       &dev_attr_test_max_freq.attr,
        &dev_attr_trans_stat.attr,
        NULL,
 };
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index 6cdd070d59c1f2..8f97c1efaacca5 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -166,6 +166,8 @@ struct devfreq {

        struct dev_pm_qos_request user_min_freq_req;
        struct dev_pm_qos_request user_max_freq_req;
+
+static ssize_t test_max_freq_show(struct device *dev, struct device_attribute *attr,
+                            char *buf)
+{
+       struct devfreq *df = to_devfreq(dev);
+       unsigned long min_freq, max_freq;
+
+       mutex_lock(&df->lock);
+       get_freq_range(df, &min_freq, &max_freq);
+       mutex_unlock(&df->lock);
+
+       return sprintf(buf, "%lu\n", max_freq);
+}
+static DEVICE_ATTR_RW(test_max_freq);
+
 static ssize_t available_frequencies_show(struct device *d,
                                          struct device_attribute *attr,
                                          char *buf)
@@ -1532,6 +1649,8 @@ static struct attribute *devfreq_attrs[] = {
        &dev_attr_polling_interval.attr,
        &dev_attr_min_freq.attr,
        &dev_attr_max_freq.attr,
+       &dev_attr_test_min_freq.attr,
+       &dev_attr_test_max_freq.attr,
        &dev_attr_trans_stat.attr,
        NULL,
 };
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index 6cdd070d59c1f2..8f97c1efaacca5 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -166,6 +166,8 @@ struct devfreq {

        struct dev_pm_qos_request user_min_freq_req;
        struct dev_pm_qos_request user_max_freq_req;
+       struct dev_pm_qos_request test_min_freq_req;
+       struct dev_pm_qos_request test_max_freq_req;
        bool stop_polling;

        unsigned long suspend_freq;


On Tue, Nov 19, 2019 at 06:12:14PM +0200, Leonard Crestez wrote:
> Switch the handling of min_freq and max_freq from sysfs to use the
> dev_pm_qos_request interface.
> 
> Since PM QoS handles frequencies as kHz this change reduces the
> precision of min_freq and max_freq. This shouldn't introduce problems
> because frequencies which are not an integer number of kHz are likely
> not an integer number of Hz either.
> 
> Try to ensure compatibility by rounding min values down and rounding
> max values up.
> 
> Signed-off-by: Leonard Crestez <[e-mail]>
> ---
>  drivers/devfreq/devfreq.c | 76 ++++++++++++++++++++++++++++++---------
>  include/linux/devfreq.h   |  9 ++---
>  2 files changed, 64 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 34bbaac6ea7e..518dd2745d06 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -139,14 +139,10 @@ static void get_freq_range(struct devfreq *devfreq,
>  	*min_freq = max(*min_freq, (unsigned long)HZ_PER_KHZ * qos_min_freq);
>  	if (qos_max_freq != PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE)
>  		*max_freq = min(*max_freq,
>  				(unsigned long)HZ_PER_KHZ * qos_max_freq);
>  
> -	/* Apply constraints from sysfs */
> -	*min_freq = max(*min_freq, devfreq->min_freq);
> -	*max_freq = min(*max_freq, devfreq->max_freq);
> -
>  	/* Apply constraints from OPP interface */
>  	*min_freq = max(*min_freq, devfreq->scaling_min_freq);
>  	*max_freq = min(*max_freq, devfreq->scaling_max_freq);
>  
>  	if (*min_freq > *max_freq)
> @@ -708,10 +704,23 @@ static void devfreq_dev_release(struct device *dev)
>  					 DEV_PM_QOS_MIN_FREQUENCY);
>  	if (err && err != -ENOENT)
>  		dev_warn(dev->parent,
>  			"Failed to remove min_freq notifier: %d\n", err);
>  
> +	if (dev_pm_qos_request_active(&devfreq->user_max_freq_req)) {
> +		err = dev_pm_qos_remove_request(&devfreq->user_max_freq_req);
> +		if (err)
> +			dev_warn(dev->parent,
> +				"Failed to remove max_freq request: %d\n", err);
> +	}
> +	if (dev_pm_qos_request_active(&devfreq->user_min_freq_req)) {
> +		err = dev_pm_qos_remove_request(&devfreq->user_min_freq_req);
> +		if (err)
> +			dev_warn(dev->parent,
> +				"Failed to remove min_freq request: %d\n", err);
> +	}
> +
>  	if (devfreq->profile->exit)
>  		devfreq->profile->exit(devfreq->dev.parent);
>  
>  	mutex_destroy(&devfreq->lock);
>  	kfree(devfreq);
> @@ -780,19 +789,17 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  	if (!devfreq->scaling_min_freq) {
>  		mutex_unlock(&devfreq->lock);
>  		err = -EINVAL;
>  		goto err_dev;
>  	}
> -	devfreq->min_freq = devfreq->scaling_min_freq;
>  
>  	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
>  	if (!devfreq->scaling_max_freq) {
>  		mutex_unlock(&devfreq->lock);
>  		err = -EINVAL;
>  		goto err_dev;
>  	}
> -	devfreq->max_freq = devfreq->scaling_max_freq;
>  
>  	devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
>  	atomic_set(&devfreq->suspend_count, 0);
>  
>  	dev_set_name(&devfreq->dev, "devfreq%d",
> @@ -829,10 +836,20 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  
>  	srcu_init_notifier_head(&devfreq->transition_notifier_list);
>  
>  	mutex_unlock(&devfreq->lock);
>  
> +	err = dev_pm_qos_add_request(dev, &devfreq->user_min_freq_req,
> +				     DEV_PM_QOS_MIN_FREQUENCY, 0);
> +	if (err < 0)
> +		goto err_devfreq;
> +	err = dev_pm_qos_add_request(dev, &devfreq->user_max_freq_req,
> +				     DEV_PM_QOS_MAX_FREQUENCY,
> +				     PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE);
> +	if (err < 0)
> +		goto err_devfreq;
> +
>  	devfreq->nb_min.notifier_call = qos_min_notifier_call;
>  	err = dev_pm_qos_add_notifier(devfreq->dev.parent, &devfreq->nb_min,
>  				      DEV_PM_QOS_MIN_FREQUENCY);
>  	if (err)
>  		goto err_devfreq;
> @@ -1414,18 +1431,26 @@ static ssize_t min_freq_store(struct device *dev, struct device_attribute *attr,
>  {
>  	struct devfreq *df = to_devfreq(dev);
>  	unsigned long value;
>  	int ret;
>  
> +	/*
> +	 * Protect against theoretical sysfs writes between
> +	 * device_add and dev_pm_qos_add_request
> +	 */
> +	if (!dev_pm_qos_request_active(&df->user_min_freq_req))
> +		return -EINVAL;
> +
>  	ret = sscanf(buf, "%lu", &value);
>  	if (ret != 1)
>  		return -EINVAL;
>  
> -	mutex_lock(&df->lock);
> -	df->min_freq = value;
> -	update_devfreq(df);
> -	mutex_unlock(&df->lock);
> +	/* Round down to kHz for PM QoS */
> +	ret = dev_pm_qos_update_request(&df->user_min_freq_req,
> +					value / HZ_PER_KHZ);
> +	if (ret < 0)
> +		return ret;
>  
>  	return count;
>  }
>  
>  static ssize_t min_freq_show(struct device *dev, struct device_attribute *attr,
> @@ -1446,22 +1471,39 @@ static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
>  {
>  	struct devfreq *df = to_devfreq(dev);
>  	unsigned long value;
>  	int ret;
>  
> +	/*
> +	 * Protect against theoretical sysfs writes between
> +	 * device_add and dev_pm_qos_add_request
> +	 */
> +	if (!dev_pm_qos_request_active(&df->user_max_freq_req))
> +		return -EINVAL;
> +
>  	ret = sscanf(buf, "%lu", &value);
>  	if (ret != 1)
>  		return -EINVAL;
>  
> -	mutex_lock(&df->lock);
> -
> -	if (!value)
> -		value = ULONG_MAX;
> +	/*
> +	 * PM QoS frequencies are in kHz so we need to convert. Convert by
> +	 * rounding upwards so that the acceptable interval never shrinks.
> +	 *
> +	 * For example if the user writes "666666666" to sysfs this value will
> +	 * be converted to 666667 kHz and back to 666667000 Hz before an OPP
> +	 * lookup, this ensures that an OPP of 666666666Hz is still accepted.
> +	 *
> +	 * A value of zero means "no limit".
> +	 */
> +	if (value)
> +		value = DIV_ROUND_UP(value, HZ_PER_KHZ);
> +	else
> +		value = PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE;
>  
> -	df->max_freq = value;
> -	update_devfreq(df);
> -	mutex_unlock(&df->lock);
> +	ret = dev_pm_qos_update_request(&df->user_max_freq_req, value);
> +	if (ret < 0)
> +		return ret;
>  
>  	return count;
>  }
>  static DEVICE_ATTR_RW(min_freq);
>  
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index 8b92ccbd1962..fb376b5b7281 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -11,10 +11,11 @@
>  #define __LINUX_DEVFREQ_H__
>  
>  #include <linux/device.h>
>  #include <linux/notifier.h>
>  #include <linux/pm_opp.h>
> +#include <linux/pm_qos.h>
>  
>  #define DEVFREQ_NAME_LEN 16
>  
>  /* DEVFREQ governor name */
>  #define DEVFREQ_GOV_SIMPLE_ONDEMAND	"simple_ondemand"
> @@ -121,12 +122,12 @@ struct devfreq_dev_profile {
>   *		devfreq.nb to the corresponding register notifier call chain.
>   * @work:	delayed work for load monitoring.
>   * @previous_freq:	previously configured frequency value.
>   * @data:	Private data of the governor. The devfreq framework does not
>   *		touch this.
> - * @min_freq:	Limit minimum frequency requested by user (0: none)
> - * @max_freq:	Limit maximum frequency requested by user (0: none)
> + * @user_min_freq_req:	PM QoS minimum frequency request from user (via sysfs)
> + * @user_max_freq_req:	PM QoS maximum frequency request from user (via sysfs)
>   * @scaling_min_freq:	Limit minimum frequency requested by OPP interface
>   * @scaling_max_freq:	Limit maximum frequency requested by OPP interface
>   * @stop_polling:	 devfreq polling status of a device.
>   * @suspend_freq:	 frequency of a device set during suspend phase.
>   * @resume_freq:	 frequency of a device set in resume phase.
> @@ -161,12 +162,12 @@ struct devfreq {
>  	unsigned long previous_freq;
>  	struct devfreq_dev_status last_status;
>  
>  	void *data; /* private data for governors */
>  
> -	unsigned long min_freq;
> -	unsigned long max_freq;
> +	struct dev_pm_qos_request user_min_freq_req;
> +	struct dev_pm_qos_request user_max_freq_req;
>  	unsigned long scaling_min_freq;
>  	unsigned long scaling_max_freq;
>  	bool stop_polling;
>  
>  	unsigned long suspend_freq;
> -- 
> 2.17.1
>

Leonard Crestez Nov. 25, 2019, 4:46 p.m. UTC | #2

On 22.11.2019 01:16, Matthias Kaehlcke wrote:
> Hi Leonard,
> 
> this seems to work ok as long as there are no other ('external') PM QoS
> requests, however the aggregate max_freq can be incorrect when there are
> multiple requests.
> 
> I intended to test with devfreq_cooling using PM QoS, but this didn't work
> out due to limitations on my development platform. Instead I added another
> set of requests and sysfs attributes to devfreq (see patch below).

Thanks a lot for looking at this.

> With this we get:
> 
> cat available_frequencies
>    180000000 267000000 355000000 430000000 565000000 650000000 800000000
> 
> # ok
> cat max_freq
>    800000000
> 
> # wtf???
> echo 650000000 > max_freq
> cat max_freq
>    800000000
> 
> # this looks better
> echo 800000000 > test_max_freq
> cat max_freq
>    650000000
> 
> 
> The problem appears to be:
> 
> #define PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE      (-1)
> 
> in include/linux/pm_qos.h (added by "PM / QoS: Restore
> DEV_PM_QOS_MIN/MAX_FREQUENCY")
> 
> The aggregate value returned by
> dev_pm_qos_read_value(dev, DEV_PM_QOS_MAX_FREQUENCY) is the
> smallest of all requests, which is PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE
> unless all requests have set an actual constraint.
> 
> You probably want to change the constant to resolve to S32_MAX or some
> other big value.

Since dev_pm_qos is now layered on top of freq_qos that should be:

#define PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE FREQ_QOS_MAX_DEFAULT_VALUE

I wrote a synthetic test and it seems your issue can be reproduced using 
kunit on top of raw freq_qos. Looking a bit deeper into pm_qos 
implementation it seems that there isn't much special treatment for 
pm_qos_constraints. A reasonable solution would be:

#define FREQ_QOS_MAX_DEFAULT_VALUE	S32_MAX

Cpufreq is not affected because it always sets "real" values but I 
believe that creating requests that should be ignored is a valid approach.

Update on pm/qos here: https://patchwork.kernel.org/cover/11260627/

--
Regards,
Leonard

Chanwoo Choi Dec. 2, 2019, 1:18 a.m. UTC | #3

On 11/20/19 1:12 AM, Leonard Crestez wrote:
> Switch the handling of min_freq and max_freq from sysfs to use the
> dev_pm_qos_request interface.
> 
> Since PM QoS handles frequencies as kHz this change reduces the
> precision of min_freq and max_freq. This shouldn't introduce problems
> because frequencies which are not an integer number of kHz are likely
> not an integer number of Hz either.
> 
> Try to ensure compatibility by rounding min values down and rounding
> max values up.
> 
> Signed-off-by: Leonard Crestez <[e-mail]>
> ---
>  drivers/devfreq/devfreq.c | 76 ++++++++++++++++++++++++++++++---------
>  include/linux/devfreq.h   |  9 ++---
>  2 files changed, 64 insertions(+), 21 deletions(-)

Acked-by: Chanwoo Choi <[e-mail]>

Thanks.

Patch

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 34bbaac6ea7e..518dd2745d06 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -139,14 +139,10 @@  static void get_freq_range(struct devfreq *devfreq,
 	*min_freq = max(*min_freq, (unsigned long)HZ_PER_KHZ * qos_min_freq);
 	if (qos_max_freq != PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE)
 		*max_freq = min(*max_freq,
 				(unsigned long)HZ_PER_KHZ * qos_max_freq);
 
-	/* Apply constraints from sysfs */
-	*min_freq = max(*min_freq, devfreq->min_freq);
-	*max_freq = min(*max_freq, devfreq->max_freq);
-
 	/* Apply constraints from OPP interface */
 	*min_freq = max(*min_freq, devfreq->scaling_min_freq);
 	*max_freq = min(*max_freq, devfreq->scaling_max_freq);
 
 	if (*min_freq > *max_freq)
@@ -708,10 +704,23 @@  static void devfreq_dev_release(struct device *dev)
 					 DEV_PM_QOS_MIN_FREQUENCY);
 	if (err && err != -ENOENT)
 		dev_warn(dev->parent,
 			"Failed to remove min_freq notifier: %d\n", err);
 
+	if (dev_pm_qos_request_active(&devfreq->user_max_freq_req)) {
+		err = dev_pm_qos_remove_request(&devfreq->user_max_freq_req);
+		if (err)
+			dev_warn(dev->parent,
+				"Failed to remove max_freq request: %d\n", err);
+	}
+	if (dev_pm_qos_request_active(&devfreq->user_min_freq_req)) {
+		err = dev_pm_qos_remove_request(&devfreq->user_min_freq_req);
+		if (err)
+			dev_warn(dev->parent,
+				"Failed to remove min_freq request: %d\n", err);
+	}
+
 	if (devfreq->profile->exit)
 		devfreq->profile->exit(devfreq->dev.parent);
 
 	mutex_destroy(&devfreq->lock);
 	kfree(devfreq);
@@ -780,19 +789,17 @@  struct devfreq *devfreq_add_device(struct device *dev,
 	if (!devfreq->scaling_min_freq) {
 		mutex_unlock(&devfreq->lock);
 		err = -EINVAL;
 		goto err_dev;
 	}
-	devfreq->min_freq = devfreq->scaling_min_freq;
 
 	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
 	if (!devfreq->scaling_max_freq) {
 		mutex_unlock(&devfreq->lock);
 		err = -EINVAL;
 		goto err_dev;
 	}
-	devfreq->max_freq = devfreq->scaling_max_freq;
 
 	devfreq->suspend_freq = dev_pm_opp_get_suspend_opp_freq(dev);
 	atomic_set(&devfreq->suspend_count, 0);
 
 	dev_set_name(&devfreq->dev, "devfreq%d",
@@ -829,10 +836,20 @@  struct devfreq *devfreq_add_device(struct device *dev,
 
 	srcu_init_notifier_head(&devfreq->transition_notifier_list);
 
 	mutex_unlock(&devfreq->lock);
 
+	err = dev_pm_qos_add_request(dev, &devfreq->user_min_freq_req,
+				     DEV_PM_QOS_MIN_FREQUENCY, 0);
+	if (err < 0)
+		goto err_devfreq;
+	err = dev_pm_qos_add_request(dev, &devfreq->user_max_freq_req,
+				     DEV_PM_QOS_MAX_FREQUENCY,
+				     PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE);
+	if (err < 0)
+		goto err_devfreq;
+
 	devfreq->nb_min.notifier_call = qos_min_notifier_call;
 	err = dev_pm_qos_add_notifier(devfreq->dev.parent, &devfreq->nb_min,
 				      DEV_PM_QOS_MIN_FREQUENCY);
 	if (err)
 		goto err_devfreq;
@@ -1414,18 +1431,26 @@  static ssize_t min_freq_store(struct device *dev, struct device_attribute *attr,
 {
 	struct devfreq *df = to_devfreq(dev);
 	unsigned long value;
 	int ret;
 
+	/*
+	 * Protect against theoretical sysfs writes between
+	 * device_add and dev_pm_qos_add_request
+	 */
+	if (!dev_pm_qos_request_active(&df->user_min_freq_req))
+		return -EINVAL;
+
 	ret = sscanf(buf, "%lu", &value);
 	if (ret != 1)
 		return -EINVAL;
 
-	mutex_lock(&df->lock);
-	df->min_freq = value;
-	update_devfreq(df);
-	mutex_unlock(&df->lock);
+	/* Round down to kHz for PM QoS */
+	ret = dev_pm_qos_update_request(&df->user_min_freq_req,
+					value / HZ_PER_KHZ);
+	if (ret < 0)
+		return ret;
 
 	return count;
 }
 
 static ssize_t min_freq_show(struct device *dev, struct device_attribute *attr,
@@ -1446,22 +1471,39 @@  static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
 {
 	struct devfreq *df = to_devfreq(dev);
 	unsigned long value;
 	int ret;
 
+	/*
+	 * Protect against theoretical sysfs writes between
+	 * device_add and dev_pm_qos_add_request
+	 */
+	if (!dev_pm_qos_request_active(&df->user_max_freq_req))
+		return -EINVAL;
+
 	ret = sscanf(buf, "%lu", &value);
 	if (ret != 1)
 		return -EINVAL;
 
-	mutex_lock(&df->lock);
-
-	if (!value)
-		value = ULONG_MAX;
+	/*
+	 * PM QoS frequencies are in kHz so we need to convert. Convert by
+	 * rounding upwards so that the acceptable interval never shrinks.
+	 *
+	 * For example if the user writes "666666666" to sysfs this value will
+	 * be converted to 666667 kHz and back to 666667000 Hz before an OPP
+	 * lookup, this ensures that an OPP of 666666666Hz is still accepted.
+	 *
+	 * A value of zero means "no limit".
+	 */
+	if (value)
+		value = DIV_ROUND_UP(value, HZ_PER_KHZ);
+	else
+		value = PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE;
 
-	df->max_freq = value;
-	update_devfreq(df);
-	mutex_unlock(&df->lock);
+	ret = dev_pm_qos_update_request(&df->user_max_freq_req, value);
+	if (ret < 0)
+		return ret;
 
 	return count;
 }
 static DEVICE_ATTR_RW(min_freq);
 
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
index 8b92ccbd1962..fb376b5b7281 100644
--- a/include/linux/devfreq.h
+++ b/include/linux/devfreq.h
@@ -11,10 +11,11 @@ 
 #define __LINUX_DEVFREQ_H__
 
 #include <linux/device.h>
 #include <linux/notifier.h>
 #include <linux/pm_opp.h>
+#include <linux/pm_qos.h>
 
 #define DEVFREQ_NAME_LEN 16
 
 /* DEVFREQ governor name */
 #define DEVFREQ_GOV_SIMPLE_ONDEMAND	"simple_ondemand"
@@ -121,12 +122,12 @@  struct devfreq_dev_profile {
  *		devfreq.nb to the corresponding register notifier call chain.
  * @work:	delayed work for load monitoring.
  * @previous_freq:	previously configured frequency value.
  * @data:	Private data of the governor. The devfreq framework does not
  *		touch this.
- * @min_freq:	Limit minimum frequency requested by user (0: none)
- * @max_freq:	Limit maximum frequency requested by user (0: none)
+ * @user_min_freq_req:	PM QoS minimum frequency request from user (via sysfs)
+ * @user_max_freq_req:	PM QoS maximum frequency request from user (via sysfs)
  * @scaling_min_freq:	Limit minimum frequency requested by OPP interface
  * @scaling_max_freq:	Limit maximum frequency requested by OPP interface
  * @stop_polling:	 devfreq polling status of a device.
  * @suspend_freq:	 frequency of a device set during suspend phase.
  * @resume_freq:	 frequency of a device set in resume phase.
@@ -161,12 +162,12 @@  struct devfreq {
 	unsigned long previous_freq;
 	struct devfreq_dev_status last_status;
 
 	void *data; /* private data for governors */
 
-	unsigned long min_freq;
-	unsigned long max_freq;
+	struct dev_pm_qos_request user_min_freq_req;
+	struct dev_pm_qos_request user_max_freq_req;
 	unsigned long scaling_min_freq;
 	unsigned long scaling_max_freq;
 	bool stop_polling;
 
 	unsigned long suspend_freq;