linux-kernel - Re: [PATCH] power:sysfs: Expose device wakeup_event

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Message-ID: <20190722182252.GA24412@kroah.com>
Date:   Mon, 22 Jul 2019 20:22:52 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ravi Chandra Sadineni <ravisadineni@...omium.org>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, rjw@...ysocki.net, pavel@....cz,
        len.brown@...el.com, bhe@...hat.com, dyoung@...hat.com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        tbroch@...omium.org
Subject: Re: [PATCH] power:sysfs: Expose device wakeup_event_count.

On Mon, Jul 22, 2019 at 11:02:58AM -0700, Ravi Chandra Sadineni wrote:
> Device level event_count can help user level daemon to track if a
> praticular device has seen an wake interrupt during a suspend resume
> cycle. Thus expose it via sysfs.
> 
> Signed-off-by: Ravi Chandra Sadineni <ravisadineni@...omium.org>
> ---
>  Documentation/ABI/testing/sysfs-devices-power | 11 ++++++++++
>  drivers/base/power/sysfs.c                    | 20 +++++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
> index 1ca04b4f0489..344549f4013f 100644
> --- a/Documentation/ABI/testing/sysfs-devices-power
> +++ b/Documentation/ABI/testing/sysfs-devices-power
> @@ -89,6 +89,17 @@ Description:
>  		attribute is not present. If the device is not enabled to wake
>  		up the system from sleep states, this attribute is empty.
>  
> +What:		/sys/devices/.../power/wakeup_event_count
> +Date:		July 2019
> +Contact:	Ravi Chandra sadineni <ravisadineni@...omium.org>
> +Description:
> +		The /sys/devices/.../wakeup_event_count attribute contains the
> +		number of signaled wakeup events associated with the device.
> +		This attribute is read-only. If the device is not capable to
> +		wake up the system from sleep states, this attribute is not
> +		present. If the device is not enabled to wake up the system
> +		from sleep states, this attribute is empty.

The attribute is not "empty" it returns just an empty line.

Is that really a good thing if you are expecting a number?

> +
>  What:		/sys/devices/.../power/wakeup_active_count
>  Date:		September 2010
>  Contact:	Rafael J. Wysocki <rjw@...ysocki.net>
> diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> index f42044d9711c..8dc1235b9784 100644
> --- a/drivers/base/power/sysfs.c
> +++ b/drivers/base/power/sysfs.c
> @@ -357,6 +357,25 @@ static ssize_t wakeup_count_show(struct device *dev,
>  
>  static DEVICE_ATTR_RO(wakeup_count);
>  
> +static ssize_t wakeup_event_count_show(struct device *dev,
> +				 struct device_attribute *attr, char *buf)
> +{
> +	unsigned long count = 0;
> +	bool enabled = false;
> +
> +	spin_lock_irq(&dev->power.lock);
> +	if (dev->power.wakeup) {
> +		count = dev->power.wakeup->event_count;
> +		enabled = true;
> +	}
> +	spin_unlock_irq(&dev->power.lock);

Why do you need to lock?  The state and count can change right after the
lock, so what does this help with?

> +	return enabled ? sprintf(buf, "%lu\n", count) : sprintf(buf, "\n");

Use a real if statement please.

> +}
> +
> +static DEVICE_ATTR_RO(wakeup_event_count);
> +
> +
> +

too many empty lines :)

thanks,

greg k-h