Re: [PATCH v2 1/2] PM / runtime: inform runtime PM of a device's next wakeup

[Lina Iyer <ilina@codeaurora.org>]

On Thu, Oct 15 2020 at 13:10 -0600, Lina Iyer wrote:
>Some devices may have a predictable interrupt pattern while executing
>usecases. An example would be the VSYNC interrupt associated with
>display devices. A 60 Hz display could cause a interrupt every 16 ms. If
>the device were in a PM domain, the domain would need to be powered up
>for device to resume and handle the interrupt.
>
>Entering a domain idle state saves power, only if the residency of the
>idle state is met. Without knowing the idle duration of the domain, the
>governor would just choose the deepest idle state that matches the QoS
>requirements. The domain might be powered off just as the device is
>expecting to wake up. If devices could inform runtime PM of their next
>event, the parent PM domain's idle duration can be determined.
>
>So let's add the pm_runtime_set_next_wake() API for the device to notify
>runtime PM of the impending wakeup and document it's usage.
>
>Signed-off-by: Lina Iyer <ilina@codeaurora.org>
>---
>Changes in v2:
>	- Update documentation
>	- Remove runtime PM enabled check
>	- Update commit text
>---
> Documentation/power/runtime_pm.rst | 23 ++++++++++++++++++++---
> drivers/base/power/runtime.c       | 24 ++++++++++++++++++++++++
> include/linux/pm.h                 |  2 ++
> include/linux/pm_runtime.h         |  1 +
> 4 files changed, 47 insertions(+), 3 deletions(-)
>
>diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
>index 0553008b6279..a1c472e5bb04 100644
>--- a/Documentation/power/runtime_pm.rst
>+++ b/Documentation/power/runtime_pm.rst
>@@ -515,6 +515,12 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
>       power.use_autosuspend isn't set, otherwise returns the expiration time
>       in jiffies
>
>+  `int pm_runtime_set_next_event(struct device *dev, ktime_t next);`
>+    - inform runtime PM of the next event on the device. Devices that are
>+      sensitive to their domain idle enter/exit latencies may provide this
>+      information for use by the PM domain governor. The domain governor would
>+      use this information to calculate it's sleep length.
>+
> It is safe to execute the following helper functions from interrupt context:
>
> - pm_request_idle()
>@@ -545,6 +551,7 @@ functions may also be used in interrupt context:
> - pm_runtime_put_sync()
> - pm_runtime_put_sync_suspend()
> - pm_runtime_put_sync_autosuspend()
>+- pm_runtime_set_next_event()
>
> 5. Runtime PM Initialization, Device Probing and Removal
> ========================================================
>@@ -639,9 +646,19 @@ suspend routine).  It may be necessary to resume the device and suspend it again
> in order to do so.  The same is true if the driver uses different power levels
> or other settings for runtime suspend and system sleep.
>
>-During system resume, the simplest approach is to bring all devices back to full
>-power, even if they had been suspended before the system suspend began.  There
>-are several reasons for this, including:
>+When a device enters idle at runtime, it may trigger the runtime PM up the
>+hierarchy and if device has a predictable interrupt pattern, we can even do a
>+better job at determining the parent's idle state. For example, a display
>+device gets a VSYNC interrupt every 16 ms when running at 60 Hz. When it's PM
>+domain is powering down and happens to be at the boundary of the VSYNC
>+interrupt, it may not be efficient to power off the domain. Knowing the next
>+wake up (when available) for devices in the domain we can determine the idle
>+duration of the domain. By comparing idle duration with the residencies of the
>+domain idle states, we can be efficient in both power and performance.
>+
>+During system resume, the simplest approach is to bring all devices back to
>+full power, even if they had been suspended before the system suspend began.
>+There are several reasons for this, including:
>
Looks like an unintended change. Will fix it in the next spin.

>   * The device might need to switch power levels, wake-up settings, etc.
>
>diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
>index 8143210a5c54..5d2ebacfd35e 100644
>--- a/drivers/base/power/runtime.c
>+++ b/drivers/base/power/runtime.c
>@@ -122,6 +122,27 @@ u64 pm_runtime_suspended_time(struct device *dev)
> }
> EXPORT_SYMBOL_GPL(pm_runtime_suspended_time);
>
>+/**
>+ * pm_runtime_set_next_wakeup_event - Notify PM framework of an impending event.
>+ * @dev: Device to handle
>+ * @next: impending interrupt/wakeup for the device
>+ */
>+int pm_runtime_set_next_event(struct device *dev, ktime_t next)
>+{
>+	unsigned long flags;
>+	int ret = -EINVAL;
>+
>+	spin_lock_irqsave(&dev->power.lock, flags);
>+	if (ktime_before(ktime_get(), next)) {
>+		dev->power.next_event = next;
>+		ret = 0;
>+	}
>+	spin_unlock_irqrestore(&dev->power.lock, flags);
>+
>+	return ret;
>+}
>+EXPORT_SYMBOL_GPL(pm_runtime_set_next_event);
>+
> /**
>  * pm_runtime_deactivate_timer - Deactivate given device's suspend timer.
>  * @dev: Device to handle.
>@@ -1415,6 +1436,9 @@ void pm_runtime_enable(struct device *dev)
> 	     "Enabling runtime PM for inactive device (%s) with active children\n",
> 	     dev_name(dev));
>
>+	/* Reset the next wakeup for the device */
>+	dev->power.next_event = KTIME_MAX;
>+
> 	spin_unlock_irqrestore(&dev->power.lock, flags);
> }
> EXPORT_SYMBOL_GPL(pm_runtime_enable);
>diff --git a/include/linux/pm.h b/include/linux/pm.h
>index a30a4b54df52..9051658674a4 100644
>--- a/include/linux/pm.h
>+++ b/include/linux/pm.h
>@@ -8,6 +8,7 @@
> #ifndef _LINUX_PM_H
> #define _LINUX_PM_H
>
>+#include <linux/ktime.h>
> #include <linux/list.h>
> #include <linux/workqueue.h>
> #include <linux/spinlock.h>
>@@ -616,6 +617,7 @@ struct dev_pm_info {
> 	u64			active_time;
> 	u64			suspended_time;
> 	u64			accounting_timestamp;
>+	ktime_t			next_event;
> #endif
> 	struct pm_subsys_data	*subsys_data;  /* Owned by the subsystem. */
> 	void (*set_latency_tolerance)(struct device *, s32);
>diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
>index 6245caa18034..af6d35178335 100644
>--- a/include/linux/pm_runtime.h
>+++ b/include/linux/pm_runtime.h
>@@ -59,6 +59,7 @@ extern void pm_runtime_get_suppliers(struct device *dev);
> extern void pm_runtime_put_suppliers(struct device *dev);
> extern void pm_runtime_new_link(struct device *dev);
> extern void pm_runtime_drop_link(struct device *dev);
>+extern int pm_runtime_set_next_event(struct device *dev, ktime_t next);
>
> /**
>  * pm_runtime_get_if_in_use - Conditionally bump up runtime PM usage counter.
>-- 
>The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>a Linux Foundation Collaborative Project
>