Re: [PATCH v2] thermal: devfreq_cooling: Use PM QoS to set frequency limits

[Chanwoo Choi <cw00.choi@samsung.com>]

On 1/17/20 8:12 AM, Matthias Kaehlcke wrote:
> Now that devfreq supports limiting the frequency range of a device
> through PM QoS make use of it instead of disabling OPPs that should
> not be used.
> 
> The switch from disabling OPPs to PM QoS introduces a subtle behavioral
> change in case of conflicting requests (min > max): PM QoS gives
> precedence to the MIN_FREQUENCY request, while higher OPPs disabled
> with dev_pm_opp_disable() would override MIN_FREQUENCY.
> 
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> 
> Changes in v2:
> - added documentation for 'req_max_freq'
> - fixed jumps in of_devfreq_cooling_register_power() unwind
> - added comment about behavioral change to the commit message
> 
>  drivers/thermal/devfreq_cooling.c | 70 ++++++++++---------------------
>  1 file changed, 23 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/thermal/devfreq_cooling.c b/drivers/thermal/devfreq_cooling.c
> index ef59256887ff63..cbbaf5bc425d1a 100644
> --- a/drivers/thermal/devfreq_cooling.c
> +++ b/drivers/thermal/devfreq_cooling.c
> @@ -24,11 +24,13 @@
>  #include <linux/idr.h>
>  #include <linux/slab.h>
>  #include <linux/pm_opp.h>
> +#include <linux/pm_qos.h>
>  #include <linux/thermal.h>
>  
>  #include <trace/events/thermal.h>
>  
> -#define SCALE_ERROR_MITIGATION 100
> +#define HZ_PER_KHZ		1000
> +#define SCALE_ERROR_MITIGATION	100
>  
>  static DEFINE_IDA(devfreq_ida);
>  
> @@ -53,6 +55,8 @@ static DEFINE_IDA(devfreq_ida);
>   *		'utilization' (which is	'busy_time / 'total_time').
>   *		The 'res_util' range is from 100 to (power_table[state] * 100)
>   *		for the corresponding 'state'.
> + * @req_max_freq:	PM QoS request for limiting the maximum frequency
> + *			of the devfreq device.
>   */
>  struct devfreq_cooling_device {
>  	int id;
> @@ -65,49 +69,9 @@ struct devfreq_cooling_device {
>  	struct devfreq_cooling_power *power_ops;
>  	u32 res_util;
>  	int capped_state;
> +	struct dev_pm_qos_request req_max_freq;
>  };
>  
> -/**
> - * partition_enable_opps() - disable all opps above a given state
> - * @dfc:	Pointer to devfreq we are operating on
> - * @cdev_state:	cooling device state we're setting
> - *
> - * Go through the OPPs of the device, enabling all OPPs until
> - * @cdev_state and disabling those frequencies above it.
> - */
> -static int partition_enable_opps(struct devfreq_cooling_device *dfc,
> -				 unsigned long cdev_state)
> -{
> -	int i;
> -	struct device *dev = dfc->devfreq->dev.parent;
> -
> -	for (i = 0; i < dfc->freq_table_size; i++) {
> -		struct dev_pm_opp *opp;
> -		int ret = 0;
> -		unsigned int freq = dfc->freq_table[i];
> -		bool want_enable = i >= cdev_state ? true : false;
> -
> -		opp = dev_pm_opp_find_freq_exact(dev, freq, !want_enable);
> -
> -		if (PTR_ERR(opp) == -ERANGE)
> -			continue;
> -		else if (IS_ERR(opp))
> -			return PTR_ERR(opp);
> -
> -		dev_pm_opp_put(opp);
> -
> -		if (want_enable)
> -			ret = dev_pm_opp_enable(dev, freq);
> -		else
> -			ret = dev_pm_opp_disable(dev, freq);
> -
> -		if (ret)
> -			return ret;
> -	}
> -
> -	return 0;
> -}
> -
>  static int devfreq_cooling_get_max_state(struct thermal_cooling_device *cdev,
>  					 unsigned long *state)
>  {
> @@ -134,7 +98,7 @@ static int devfreq_cooling_set_cur_state(struct thermal_cooling_device *cdev,
>  	struct devfreq_cooling_device *dfc = cdev->devdata;
>  	struct devfreq *df = dfc->devfreq;
>  	struct device *dev = df->dev.parent;
> -	int ret;
> +	unsigned long freq;
>  
>  	if (state == dfc->cooling_state)
>  		return 0;
> @@ -144,9 +108,10 @@ static int devfreq_cooling_set_cur_state(struct thermal_cooling_device *cdev,
>  	if (state >= dfc->freq_table_size)
>  		return -EINVAL;
>  
> -	ret = partition_enable_opps(dfc, state);
> -	if (ret)
> -		return ret;
> +	freq = dfc->freq_table[state];
> +
> +	dev_pm_qos_update_request(&dfc->req_max_freq,
> +				  DIV_ROUND_UP(freq, HZ_PER_KHZ));
>  
>  	dfc->cooling_state = state;
>  
> @@ -529,9 +494,15 @@ of_devfreq_cooling_register_power(struct device_node *np, struct devfreq *df,
>  	if (err)
>  		goto free_dfc;
>  
> -	err = ida_simple_get(&devfreq_ida, 0, 0, GFP_KERNEL);
> +	err = dev_pm_qos_add_request(df->dev.parent, &dfc->req_max_freq,
> +				     DEV_PM_QOS_MAX_FREQUENCY,
> +				     PM_QOS_MAX_FREQUENCY_DEFAULT_VALUE);
>  	if (err < 0)
>  		goto free_tables;
> +
> +	err = ida_simple_get(&devfreq_ida, 0, 0, GFP_KERNEL);
> +	if (err < 0)
> +		goto remove_qos_req;
>  	dfc->id = err;
>  
>  	snprintf(dev_name, sizeof(dev_name), "thermal-devfreq-%d", dfc->id);
> @@ -552,6 +523,10 @@ of_devfreq_cooling_register_power(struct device_node *np, struct devfreq *df,
>  
>  release_ida:
>  	ida_simple_remove(&devfreq_ida, dfc->id);
> +
> +remove_qos_req:
> +	dev_pm_qos_remove_request(&dfc->req_max_freq);
> +
>  free_tables:
>  	kfree(dfc->power_table);
>  	kfree(dfc->freq_table);
> @@ -600,6 +575,7 @@ void devfreq_cooling_unregister(struct thermal_cooling_device *cdev)
>  
>  	thermal_cooling_device_unregister(dfc->cdev);
>  	ida_simple_remove(&devfreq_ida, dfc->id);
> +	dev_pm_qos_remove_request(&dfc->req_max_freq);
>  	kfree(dfc->power_table);
>  	kfree(dfc->freq_table);
>  
> 

Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics