linux-kernel - Re: [PATCH 3/3] devfreq: Add current freq callback in device profile

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Date:	Mon, 10 Sep 2012 00:00:24 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Rajagopal Venkat <rajagopal.venkat@...aro.org>
Cc:	mturquette@...aro.org, myungjoo.ham@...sung.com,
	kyungmin.park@...sung.com, patches@...aro.org,
	linaro-dev@...ts.linaro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] devfreq: Add current freq callback in device profile

On Monday, September 03, 2012, Rajagopal Venkat wrote:
> Devfreq returns governor predicted frequency as current
> frequency via sysfs interface. But device may not support
> all frequencies that governor predicts.

Do you have any examples, even out of the tree?

> Its driver
> responsibility to maintain current frequency at which device
> is operating. Add a callback in device profile to fix this.

Obviously, there are no users of this callback in the tree right now, so it
may not be regarded as a fix.  I'd rather say it's a new mechanism for
drivers to use if their current frequencies differ from the governor-selected
ones.

> Also add a new sysfs node to expose governor predicted next
> target frequency.
> 
> Signed-off-by: Rajagopal Venkat <rajagopal.venkat@...aro.org>
> ---
>  Documentation/ABI/testing/sysfs-class-devfreq |  7 +++++++
>  drivers/devfreq/devfreq.c                     | 14 ++++++++++++++
>  include/linux/devfreq.h                       |  3 +++
>  3 files changed, 24 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
> index 23d78b5..9df5205 100644
> --- a/Documentation/ABI/testing/sysfs-class-devfreq
> +++ b/Documentation/ABI/testing/sysfs-class-devfreq
> @@ -21,6 +21,13 @@ Description:
>  		The /sys/class/devfreq/.../cur_freq shows the current
>  		frequency of the corresponding devfreq object.
>  
> +What:		/sys/class/devfreq/.../target_freq
> +Date:		September 2012
> +Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>

It's a bit odd to add someone else as a contact for interfaces that you're
introducing.  I'd need MyungJoo Ham's ACK for that.

> +Description:
> +		The /sys/class/devfreq/.../target_freq shows the next governor
> +		predicted target frequency of the corresponding devfreq object.
> +
>  What:		/sys/class/devfreq/.../central_polling
>  Date:		September 2011
>  Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 3a5f126..55e9046 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -400,6 +400,19 @@ static ssize_t show_governor(struct device *dev,
>  static ssize_t show_freq(struct device *dev,
>  			 struct device_attribute *attr, char *buf)
>  {
> +	unsigned long freq;
> +	struct devfreq *devfreq = to_devfreq(dev);
> +
> +	if (devfreq->profile->get_cur_freq)
> +		if (!devfreq->profile->get_cur_freq(devfreq->dev.parent, &freq))

That should be

+	if (devfreq->profile->get_cur_freq
+	    && !devfreq->profile->get_cur_freq(devfreq->dev.parent, &freq))

> +			return sprintf(buf, "%lu\n", freq);
> +

Moreover, I suppose it should fall back to the current behavior if
.get_cur_freq() is not present.

> +	return sprintf(buf, "<unknown>");
> +}
> +
> +static ssize_t show_target_freq(struct device *dev,
> +			struct device_attribute *attr, char *buf)
> +{
>  	return sprintf(buf, "%lu\n", to_devfreq(dev)->previous_freq);
>  }
>  
> @@ -503,6 +516,7 @@ static ssize_t show_max_freq(struct device *dev, struct device_attribute *attr,
>  static struct device_attribute devfreq_attrs[] = {
>  	__ATTR(governor, S_IRUGO, show_governor, NULL),
>  	__ATTR(cur_freq, S_IRUGO, show_freq, NULL),
> +	__ATTR(target_freq, S_IRUGO, show_target_freq, NULL),
>  	__ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
>  	       store_polling_interval),
>  	__ATTR(min_freq, S_IRUGO | S_IWUSR, show_min_freq, store_min_freq),
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index 7c7e179..d12ed41 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -66,6 +66,8 @@ struct devfreq_dev_status {
>   *			explained above with "DEVFREQ_FLAG_*" macros.
>   * @get_dev_status	The device should provide the current performance
>   *			status to devfreq, which is used by governors.
> + * @get_cur_freq	The device should provide the current frequency
> + *			at which it is operating.
>   * @exit		An optional callback that is called when devfreq
>   *			is removing the devfreq object due to error or
>   *			from devfreq_remove_device() call. If the user
> @@ -79,6 +81,7 @@ struct devfreq_dev_profile {
>  	int (*target)(struct device *dev, unsigned long *freq, u32 flags);
>  	int (*get_dev_status)(struct device *dev,
>  			      struct devfreq_dev_status *stat);
> +	int (*get_cur_freq)(struct device *dev, unsigned long *freq);
>  	void (*exit)(struct device *dev);
>  };

Thanks,
Rafael
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