linux-kernel - Re: [RFC v2 2/5] PM, Add sysfs file power_off to control device power off policy

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Date:	Fri, 4 May 2012 13:50:55 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Huang Ying <ying.huang@...el.com>
Cc:	ming.m.lin@...el.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Zheng Yan <zheng.z.yan@...el.com>,
	Lan Tianyu <tianyu.lan@...el.com>
Subject: Re: [RFC v2 2/5] PM, Add sysfs file power_off to control device power
 off policy

On Fri, May 4, 2012 at 2:13 AM, Huang Ying <ying.huang@...el.com> wrote:
> From: Lan Tianyu <tianyu.lan@...el.com>
>
> Some devices can be powered off to save more power via some platform
> mechanism, e.g., ACPI.  But that may not work as expected for some
> device or platform.  So, this patch adds a sysfs file named power_off
> under <device>/power directory to provide a mechanism for user to control
> whether to allow the device to be power off.
>
> power_off => "enabled" means allowing the device to be powered off if
> possible.
>
> power_off => "disabled" means the device must be power on anytime.
>
> Also add flag power_off_user to struct dev_pm_info to record users'
> choice. The bus layer can use this field to determine whether to
> power off the device.

My first thought was that writing to "power_off" would actually turn
the power off, which isn't true.  Maybe something like
"poweroff_allowed" would work.

I think there's only one use of this new field, in
pci_pm_runtime_suspend().  Maybe you could pull out that hunk from
patch 5, combine it with this one, and move it to after patch 5?

> Signed-off-by: Lan Tianyu <tianyu.lan@...el.com>
> Signed-off-by: Huang Ying <ying.huang@...el.com>
> ---
>  drivers/base/power/sysfs.c |   33 +++++++++++++++++++++++++++++++++
>  include/linux/pm.h         |    1 +
>  2 files changed, 34 insertions(+)
>
> --- a/drivers/base/power/sysfs.c
> +++ b/drivers/base/power/sysfs.c
> @@ -243,6 +243,38 @@ static ssize_t pm_qos_latency_store(stru
>
>  static DEVICE_ATTR(pm_qos_resume_latency_us, 0644,
>                   pm_qos_latency_show, pm_qos_latency_store);
> +
> +static ssize_t power_off_show(struct device *dev,
> +                             struct device_attribute *attr, char *buf)
> +{
> +       return sprintf(buf, "%s\n",
> +                      dev->power.power_off_user ? enabled : disabled);
> +}
> +
> +static ssize_t power_off_store(struct device * dev,
> +                              struct device_attribute *attr,
> +                              const char * buf, size_t n)
> +{
> +       char *cp;
> +       int len = n;
> +       unsigned int power_off_user;
> +
> +       cp = memchr(buf, '\n', n);
> +       if (cp)
> +               len = cp - buf;
> +
> +       if (len == sizeof enabled - 1 && strncmp(buf, enabled, len) == 0)
> +               dev->power.power_off_user = true;
> +       else if (len == sizeof disabled - 1 && strncmp(buf, disabled, len) == 0)
> +               dev->power.power_off_user = false;
> +       else
> +               return -EINVAL;
> +
> +       pm_runtime_resume(dev);
> +       return n;
> +
> +}
> +static DEVICE_ATTR(power_off, 0644, power_off_show, power_off_store);
>  #endif /* CONFIG_PM_RUNTIME */
>
>  #ifdef CONFIG_PM_SLEEP
> @@ -508,6 +540,7 @@ static struct attribute *runtime_attrs[]
>        &dev_attr_runtime_suspended_time.attr,
>        &dev_attr_runtime_active_time.attr,
>        &dev_attr_autosuspend_delay_ms.attr,
> +       &dev_attr_power_off.attr,
>  #endif /* CONFIG_PM_RUNTIME */
>        NULL,
>  };
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -537,6 +537,7 @@ struct dev_pm_info {
>        unsigned int            use_autosuspend:1;
>        unsigned int            timer_autosuspends:1;
>        unsigned int            power_must_be_on:1;
> +       unsigned int            power_off_user:1;

This name definitely doesn't suggest anything useful  I think
"poweroff_allowed" or similar would make a lot more sense when reading
the code.

>        enum rpm_request        request;
>        enum rpm_status         runtime_status;
>        int                     runtime_error;
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