On Fri, 28 May 2021 at 17:27, Alan Stern [off-list ref] wrote:

On Fri, May 28, 2021 at 11:12:02AM +0200, Ulf Hansson wrote:

quoted

We are currently allowing ->rpm_idle() callbacks to be unassigned without
returning an error code from rpm_idle(). This has been useful to avoid
boilerplate code in drivers. Let's take this approach a step further, by
allowing unassigned ->runtime_suspend|resume() callbacks as well.

In this way, a consumer/supplier device link can be used to let a consumer
device be power managed through its supplier device, without requiring
assigned ->runtime_suspend|resume() callbacks for the consumer device, for
example.

Signed-off-by: Ulf Hansson <redacted>
---
 drivers/base/power/runtime.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 68bebbf81347..8a66eaf731e4 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c

@@ -345,7 +345,7 @@ static void rpm_suspend_suppliers(struct device *dev)
 static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
      __releases(&dev->power.lock) __acquires(&dev->power.lock)
 {
-     int retval, idx;
+     int retval = 0, idx;
      bool use_links = dev->power.links_count > 0;

      if (dev->power.irq_safe) {

@@ -373,7 +373,8 @@ static int __rpm_callback(int (*cb)(struct device *), struct device *dev)
              }
      }

-     retval = cb(dev);
+     if (cb)
+             retval = cb(dev);

      if (dev->power.irq_safe) {
              spin_lock(&dev->power.lock);

@@ -484,9 +485,6 @@ static int rpm_callback(int (*cb)(struct device *), struct device *dev)
 {
      int retval;

-     if (!cb)
-             return -ENOSYS;

This is a change in behavior, right?  What about drivers or subsystems
that don't support runtime PM and consequently don't have any RPM
callbacks assigned?

Yes, you are right.

However, drivers/subsystems that support runtime PM should also call
pm_runtime_enable() and if they don't, the rpm_callback() should not
get called for them.

Then, at least to me, I think it would be quite odd that a
subsystem/driver that calls pm_runtime_enable(), would be checking
return values from pm_runtime_get|put_*() for -ENOSYS? I mean, why
bother calling pm_runtime_enable() in the first place?

Also, assuming Rafael accepts this change, don't you also need to update
the runtime-PM documentation?

Good point, thanks! Let me add a patch updating the docs.

Alan Stern

Kind regards
Uffe

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