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Date:   Mon, 18 Jan 2021 18:17:16 +0100
From:   Greg KH <greg@kroah.com>
To:     Lukasz Luba <lukasz.luba@arm.com>
Cc:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        cw00.choi@samsung.com, myungjoo.ham@samsung.com,
        kyungmin.park@samsung.com
Subject: Re: [PATCH] PM / devfreq: Add sysfs attributes to simple_ondemand
 governor
Message-ID: <YAXCnMsUy3n+asfm@kroah.com>
References: <20210115170530.22603-1-lukasz.luba@arm.com>
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In-Reply-To: <20210115170530.22603-1-lukasz.luba@arm.com>
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On Fri, Jan 15, 2021 at 05:05:30PM +0000, Lukasz Luba wrote:
> The simple_ondemand devfreq governor is used by quite a few devices, like
> GPUs, DSPs, memory controllers, etc. It implements algorithm which tries
> to predict the device frequency based on past statistics. There are two
> tunables for the algorithm: 'upthreshold' and 'downdifferential'. These
> tunables change the behavior of the decision, e.g. how fast to increase
> the frequency or how rapidly limit the frequency. These values might be
> different based on the application which is currently running, e.g.
> different behavior is needed for a game than for web browsing or clean
> desktop. The patch exports these two tunables so they can be adjusted
> based on current need. There is also a check with the allowed ranges
> to make sure the values are correct and safe.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>  drivers/devfreq/governor_simpleondemand.c | 135 ++++++++++++++++++++++
>  1 file changed, 135 insertions(+)
> 
> diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
> index d57b82a2b570..4b3c182e0a49 100644
> --- a/drivers/devfreq/governor_simpleondemand.c
> +++ b/drivers/devfreq/governor_simpleondemand.c
> @@ -15,6 +15,7 @@
>  /* Default constants for DevFreq-Simple-Ondemand (DFSO) */
>  #define DFSO_UPTHRESHOLD	(90)
>  #define DFSO_DOWNDIFFERENCTIAL	(5)
> +#define DFSO_MAX_VALUE		(100)
>  static int devfreq_simple_ondemand_func(struct devfreq *df,
>  					unsigned long *freq)
>  {
> @@ -84,15 +85,149 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>  	return 0;
>  }
>  
> +static ssize_t upthreshold_show(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	struct devfreq_simple_ondemand_data *data;
> +	struct devfreq *df = to_devfreq(dev);
> +
> +	if (!df->data)
> +		return -EINVAL;
> +
> +	data = df->data;
> +
> +	return sprintf(buf, "%d\n", data->upthreshold);

sysfs_emit()?

Also, you forgot the Documentation/ABI/ updates for new sysfs files :(


> +}
> +
> +static ssize_t upthreshold_store(struct device *dev,
> +				 struct device_attribute *attr,
> +				 const char *buf, size_t count)
> +{
> +	struct devfreq_simple_ondemand_data *data;
> +	struct devfreq *df = to_devfreq(dev);
> +	unsigned int value;
> +	int ret;
> +
> +	if (!df->data)
> +		return -EINVAL;
> +
> +	data = df->data;
> +
> +	ret = kstrtouint(buf, 10, &value);
> +	if (ret < 0)
> +		return -EINVAL;
> +
> +	mutex_lock(&df->lock);
> +
> +	if (value > DFSO_MAX_VALUE || value <= data->downdifferential) {
> +		mutex_unlock(&df->lock);
> +		return -EINVAL;
> +	}
> +
> +	data->upthreshold = value;
> +	mutex_unlock(&df->lock);
> +
> +	return count;
> +}
> +static DEVICE_ATTR_RW(upthreshold);
> +
> +static ssize_t downdifferential_show(struct device *dev,
> +				     struct device_attribute *attr, char *buf)
> +{
> +	struct devfreq_simple_ondemand_data *data;
> +	struct devfreq *df = to_devfreq(dev);
> +
> +	if (!df->data)
> +		return -EINVAL;
> +
> +	data = df->data;
> +
> +	return sprintf(buf, "%d\n", data->downdifferential);
> +}
> +
> +static ssize_t downdifferential_store(struct device *dev,
> +				      struct device_attribute *attr,
> +				      const char *buf, size_t count)
> +{
> +	struct devfreq_simple_ondemand_data *data;
> +	struct devfreq *df = to_devfreq(dev);
> +	unsigned int value;
> +	int ret;
> +
> +	if (!df->data)
> +		return -EINVAL;
> +
> +	data = df->data;
> +
> +	ret = kstrtouint(buf, 10, &value);
> +	if (ret < 0)
> +		return -EINVAL;
> +
> +	mutex_lock(&df->lock);
> +
> +	if (value > DFSO_MAX_VALUE || value >= data->upthreshold) {
> +		mutex_unlock(&df->lock);
> +		return -EINVAL;
> +	}
> +
> +	data->downdifferential = value;
> +	mutex_unlock(&df->lock);
> +
> +	return count;
> +}
> +static DEVICE_ATTR_RW(downdifferential);
> +
> +static void devfreq_simple_ondemand_sysfs_setup(struct devfreq *df)
> +{
> +	struct devfreq_simple_ondemand_data *data;
> +	int ret;
> +
> +	if (!df->data) {
> +		/* The memory will be freed automatically */
> +		df->data = devm_kzalloc(&df->dev,
> +				sizeof(struct devfreq_simple_ondemand_data),
> +				GFP_KERNEL);
> +		if (!df->data) {
> +			dev_warn(&df->dev, "Unable to allocate memory");
> +			return;
> +		}
> +	}
> +
> +	data = df->data;
> +
> +	/* After new allocation setup default values, since they are used */
> +	if (!data->upthreshold)
> +		data->upthreshold = DFSO_UPTHRESHOLD;
> +
> +	if (!data->downdifferential)
> +		data->downdifferential = DFSO_DOWNDIFFERENCTIAL;
> +
> +	ret = sysfs_create_file(&df->dev.kobj, &dev_attr_upthreshold.attr);
> +	if (ret < 0)
> +		dev_warn(&df->dev, "Unable to create 'upthreshold' attr\n");
> +
> +	ret = sysfs_create_file(&df->dev.kobj, &dev_attr_downdifferential.attr);
> +	if (ret < 0)
> +		dev_warn(&df->dev, "Unable to create 'downdifferential' attr\n");

You just raced with userspace and lost :(

Please use the default sysfs groups so that it all works properly.

Huge hint, when calling sysfs_* from a driver, that usually means you
are doing something wrong.

thanks,

greg k-h