PM: runtime: Capture device status before disabling runtime PM

In some cases (for example, during system-wide suspend and resume of
devices) it is useful to know whether or not runtime PM has ever been
enabled for a given device and, if so, what the runtime PM status of
it had been right before runtime PM was disabled for it last time.

For this reason, introduce a new struct dev_pm_info field called
last_status that will be used for capturing the runtime PM status of
the device when its power.disable_depth counter changes from 0 to 1.

The new field will be set to RPM_INVALID to start with and whenever
power.disable_depth changes from 1 to 0, so it will be valid only
when runtime PM of the device is currently disabled, but it has been
enabled at least once.

Immediately use power.last_status in rpm_resume() to make it handle
the case when PM runtime is disabled for the device, but its runtime
PM status is RPM_ACTIVE more consistently.  Namely, make it return 1
if power.last_status is also equal to RPM_ACTIVE in that case (the
idea being that if the status was RPM_ACTIVE last time when
power.disable_depth was changing from 0 to 1 and it is still
RPM_ACTIVE, it can be assumed to reflect what happened to the device
last time when it was using runtime PM) and -EACCES otherwise.

Update the documentation to provide a description of last_status and
change the description of pm_runtime_resume() in it to reflect the
new behavior of rpm_active().

While at it, rearrange the code in pm_runtime_enable() to be more
straightforward and replace the WARN() macro in it with a pr_warn()
invocation which is less disruptive.

Link: https://lore.kernel.org/linux-pm/20211026222626.39222-1-ulf.hansson@linaro.org/t/#u
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
index d6bf84f..65b86e4 100644 (file)
--- a/Documentation/power/runtime_pm.rst
+++ b/Documentation/power/runtime_pm.rst
@@ -265,6 +265,10 @@ defined in include/linux/pm.h:
       RPM_SUSPENDED, which means that each device is initially regarded by the
       PM core as 'suspended', regardless of its real hardware status
 
+  `enum rpm_status last_status;`
+    - the last runtime PM status of the device captured before disabling runtime
+      PM for it (invalid initially and when disable_depth is 0)
+
   `unsigned int runtime_auto;`
     - if set, indicates that the user space has allowed the device driver to
       power manage the device at run time via the /sys/devices/.../power/control
@@ -333,10 +337,12 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
 
   `int pm_runtime_resume(struct device *dev);`
     - execute the subsystem-level resume callback for the device; returns 0 on
-      success, 1 if the device's runtime PM status was already 'active' or
-      error code on failure, where -EAGAIN means it may be safe to attempt to
-      resume the device again in future, but 'power.runtime_error' should be
-      checked additionally, and -EACCES means that 'power.disable_depth' is
+      success, 1 if the device's runtime PM status is already 'active' (also if
+      'power.disable_depth' is nonzero, but the status was 'active' when it was
+      changing from 0 to 1) or error code on failure, where -EAGAIN means it may
+      be safe to attempt to resume the device again in future, but
+      'power.runtime_error' should be checked additionally, and -EACCES means
+      that the callback could not be run, because 'power.disable_depth' was
       different from 0
 
   `int pm_runtime_resume_and_get(struct device *dev);`

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index d504cd4..844b6b8 100644 (file)
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -742,13 +742,15 @@ static int rpm_resume(struct device *dev, int rpmflags)
        trace_rpm_resume_rcuidle(dev, rpmflags);
 
  repeat:
-       if (dev->power.runtime_error)
+       if (dev->power.runtime_error) {
                retval = -EINVAL;
-       else if (dev->power.disable_depth == 1 && dev->power.is_suspended
-           && dev->power.runtime_status == RPM_ACTIVE)
-               retval = 1;
-       else if (dev->power.disable_depth > 0)
-               retval = -EACCES;
+       } else if (dev->power.disable_depth > 0) {
+               if (dev->power.runtime_status == RPM_ACTIVE &&
+                   dev->power.last_status == RPM_ACTIVE)
+                       retval = 1;
+               else
+                       retval = -EACCES;
+       }
        if (retval)
                goto out;
 
@@ -1410,8 +1412,10 @@ void __pm_runtime_disable(struct device *dev, bool check_resume)
        /* Update time accounting before disabling PM-runtime. */
        update_pm_runtime_accounting(dev);
 
-       if (!dev->power.disable_depth++)
+       if (!dev->power.disable_depth++) {
                __pm_runtime_barrier(dev);
+               dev->power.last_status = dev->power.runtime_status;
+       }
 
  out:
        spin_unlock_irq(&dev->power.lock);
@@ -1428,23 +1432,23 @@ void pm_runtime_enable(struct device *dev)
 
        spin_lock_irqsave(&dev->power.lock, flags);
 
-       if (dev->power.disable_depth > 0) {
-               dev->power.disable_depth--;
-
-               /* About to enable runtime pm, set accounting_timestamp to now */
-               if (!dev->power.disable_depth)
-                       dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
-       } else {
+       if (!dev->power.disable_depth) {
                dev_warn(dev, "Unbalanced %s!\n", __func__);
+               goto out;
        }
 
-       WARN(!dev->power.disable_depth &&
-            dev->power.runtime_status == RPM_SUSPENDED &&
-            !dev->power.ignore_children &&
-            atomic_read(&dev->power.child_count) > 0,
-            "Enabling runtime PM for inactive device (%s) with active children\n",
-            dev_name(dev));
+       if (--dev->power.disable_depth > 0)
+               goto out;
 
+       dev->power.last_status = RPM_INVALID;
+       dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
+
+       if (dev->power.runtime_status == RPM_SUSPENDED &&
+           !dev->power.ignore_children &&
+           atomic_read(&dev->power.child_count) > 0)
+               dev_warn(dev, "Enabling runtime PM for inactive device with active children\n");
+
+out:
        spin_unlock_irqrestore(&dev->power.lock, flags);
 }
 EXPORT_SYMBOL_GPL(pm_runtime_enable);
@@ -1640,6 +1644,7 @@ EXPORT_SYMBOL_GPL(__pm_runtime_use_autosuspend);
 void pm_runtime_init(struct device *dev)
 {
        dev->power.runtime_status = RPM_SUSPENDED;
+       dev->power.last_status = RPM_INVALID;
        dev->power.idle_notification = false;
 
        dev->power.disable_depth = 1;

diff --git a/include/linux/pm.h b/include/linux/pm.h
index fc9691c..e1e9402 100644 (file)
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -521,6 +521,7 @@ const struct dev_pm_ops __maybe_unused name = { \
  */
 
 enum rpm_status {
+       RPM_INVALID = -1,
        RPM_ACTIVE = 0,
        RPM_RESUMING,
        RPM_SUSPENDED,
@@ -634,6 +635,7 @@ struct dev_pm_info {
        unsigned int            links_count;
        enum rpm_request        request;
        enum rpm_status         runtime_status;
+       enum rpm_status         last_status;
        int                     runtime_error;
        int                     autosuspend_delay;
        u64                     last_busy;