On Mon, Nov 30, 2020 at 7:50 PM Laurent Pinchart
[off-list ref] wrote:

Hi Rafael,

On Mon, Nov 30, 2020 at 06:55:57PM +0100, Rafael J. Wysocki wrote:

quoted

On Mon, Nov 30, 2020 at 6:35 PM Laurent Pinchart wrote:

quoted

On Mon, Nov 30, 2020 at 05:37:52PM +0100, Rafael J. Wysocki wrote:

quoted

On Fri, Nov 27, 2020 at 11:16 AM Geert Uytterhoeven wrote:

quoted

On Tue, Nov 10, 2020 at 10:29 AM Zhang Qilong [off-list ref] wrote:

quoted

In many case, we need to check return value of pm_runtime_get_sync, but
it brings a trouble to the usage counter processing. Many callers forget
to decrease the usage counter when it failed, which could resulted in
reference leak. It has been discussed a lot[0][1]. So we add a function
to deal with the usage counter for better coding.

[0]https://lkml.org/lkml/2020/6/14/88
[1]https://patchwork.ozlabs.org/project/linux-tegra/list/?series=178139
Signed-off-by: Zhang Qilong <redacted>

Thanks for your patch, which is now commit dd8088d5a8969dc2 ("PM:
runtime: Add pm_runtime_resume_and_get to deal with usage counter") in
v5.10-rc5.

quoted

--- a/include/linux/pm_runtime.h
+++ b/include/linux/pm_runtime.h

@@ -386,6 +386,27 @@ static inline int pm_runtime_get_sync(struct device *dev)
        return __pm_runtime_resume(dev, RPM_GET_PUT);
 }

+/**
+ * pm_runtime_resume_and_get - Bump up usage counter of a device and resume it.
+ * @dev: Target device.
+ *
+ * Resume @dev synchronously and if that is successful, increment its runtime
+ * PM usage counter. Return 0 if the runtime PM usage counter of @dev has been
+ * incremented or a negative error code otherwise.
+ */
+static inline int pm_runtime_resume_and_get(struct device *dev)

Perhaps this function should be called pm_runtime_resume_and_get_sync(),

No, really.

I might consider calling it pm_runtime_acquire(), and adding a
matching _release() as a pm_runtime_get() synonym for that matter, but
not the above.

pm_runtime_acquire() seems better to me too. Would pm_runtime_release()
would be an alias for pm_runtime_put() ?

Yes.  This covers all of the use cases relevant for drivers AFAICS.

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We would also likely need a pm_runtime_release_autosuspend() too then.

Why would we?

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But on that topic, I was wondering, is there a reason we can't select
autosuspend behaviour automatically when autosuspend is enabled ?

That is the case already.

pm_runtime_put() will autosuspend if enabled and the usage counter is
0, as long as ->runtime_idle() returns 0 (or is absent).

pm_runtime_put_autosuspend() is an optimization allowing
->runtime_idle() to be skipped entirely, but I'm wondering how many
users really need that.

Ah, I didn't know that, that's good to know. We then don't need
pm_runtime_release_autosuspend() (unless the optimization really makes a
big difference).

Should I write new drievr code with pm_runtime_put() instead of
pm_runtime_put_autosuspend() ?

If you don't have ->runtime_idle() in the driver (and in the bus type
generally speaking, but none of them provide it IIRC),
pm_runtime_put() is basically equivalent to
pm_runtime_put_autosuspend() AFAICS, except for some extra checks done
by the former.

Otherwise it all depends on what the ->runtime_idle() callback does,
but it is hard to imagine a practical use case when the difference
would be really meaningful.

I haven't found clear guidelines on this in the documentation.

Yes, that's one of the items I need to take care of.