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    SubjectRe: [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@intel.com> wrote:
    > From: Lan Tianyu <tianyu.lan@intel.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@intel.com>
    > Signed-off-by: Huang Ying <ying.huang@intel.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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