[PATCH] PM / Runtime: Defer resuming of the device in pm_runtime_force_resume()

[Ulf Hansson]

When the pm_runtime_force_suspend|resume() helpers were invented, we still
had CONFIG_PM_RUNTIME and CONFIG_PM_SLEEP as separate Kconfig options.

To make sure these helpers worked for all combinations and without
introducing too much of complexity, the device was always resumed in
pm_runtime_force_resume().

More precisely, when CONFIG_PM_SLEEP was set and CONFIG_PM_RUNTIME was
unset, we needed to resume the device as the subsystem/driver couldn't
rely on using runtime PM to do it.

As the CONFIG_PM_RUNTIME option was merged into CONFIG_PM a while ago, it
removed this combination, of using CONFIG_PM_SLEEP without the earlier
CONFIG_PM_RUNTIME.

For this reason we can now rely on the subsystem/driver to use runtime PM
to resume the device, instead of forcing that to be done in all cases. In
other words, let's defer this to a later point when it's actually needed.

Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
---

Note, this patch is based upon another not yet queued patch [1]. The reason is
simply because that [1] is a more important patch as it fixes a problem. It was
posted to linux-pm April 8th and I expect it (or a new revision of it) to be
applied before $subject patch.

[1]
https://patchwork.kernel.org/patch/8782851

---
 drivers/base/power/runtime.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index b746904..a190ca0 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -1506,6 +1506,17 @@ int pm_runtime_force_resume(struct device *dev)
 		goto out;
 	}
 
+	/*
+	 * The PM core increases the runtime PM usage count in the system PM
+	 * prepare phase. If the count is greather than 1 at this point, someone
+	 * else has also increased it. In such case, let's make sure to runtime
+	 * resume the device as that is likely what is expected. In other case
+	 * we trust the subsystem/driver to runtime resume the device when it's
+	 * actually needed.
+	 */
+	if (atomic_read(&dev->power.usage_count) < 2)
+		goto out;
+
 	ret = pm_runtime_set_active(dev);
 	if (ret)
 		goto out;
-- 
1.9.1