[RFC v2 2/5] PM, Add sysfs file power_off to control device power off policy

[Huang Ying <ying.huang@intel.com>]

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.

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