Re: [PATCH v5 02/12] PM / devfreq: Fix handling of min/max_freq == 0

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

Hi Matthias,

On 2018년 07월 04일 08:46, Matthias Kaehlcke wrote:
> 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>
> ---
> 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 0057ef5b0a98..6f604f8b2b81 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 */
>  	}
> @@ -1122,18 +1122,27 @@ static ssize_t min_freq_store(struct device *dev, struct device_attribute *attr,
>  {
>  	struct devfreq *df = to_devfreq(dev);
>  	unsigned long value;
> +	unsigned long *freq_table;

You can move 'freq_table' under 'else' statement.

>  	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 {
> +		freq_table = df->profile->freq_table;
> +		/* typical order is ascending, some drivers use descending */

You better to explain what is doing of following code.
How about modifying it as following?

		/* Get minimum frequency according to sorting way */

> +		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;
> @@ -1157,18 +1166,27 @@ static ssize_t max_freq_store(struct device *dev, struct device_attribute *attr,
>  {
>  	struct devfreq *df = to_devfreq(dev);
>  	unsigned long value;
> +	unsigned long *freq_table;

ditto. You can move 'freq_table' under 'else' statement.

>  	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 {
> +		freq_table = df->profile->freq_table;
> +		/* typical order is ascending, some drivers use descending */

ditto.
		/* Get maximum frequency according to sorting way */

> +		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;
> 

If you agree my comment and modify this patch according to my comment,
feel free to add my review tag.
- Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics