Re: [PATCH v2 3/3] PM: runtime: Clarify documentation when callbacks are unassigned

On Tue, 8 Jun 2021 at 16:49, Alan Stern [off-list ref] wrote:

On Tue, Jun 08, 2021 at 04:30:48PM +0200, Ulf Hansson wrote:

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On Tue, 8 Jun 2021 at 16:23, Alan Stern [off-list ref] wrote:

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On Tue, Jun 08, 2021 at 11:02:50AM +0200, Ulf Hansson wrote:

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Recent changes to the PM core allows ->runtime_suspend|resume callbacks to
be unassigned.

In the earlier behaviour the PM core would return -ENOSYS, when trying to
runtime resume a device, for example. Let's update the documentation to
clarify this.

Signed-off-by: Ulf Hansson <redacted>
---

Changes in v2:
      - Added a new patch for the updating the docs, as pointed out by Alan.

---
 Documentation/power/runtime_pm.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
index 18ae21bf7f92..3d09c9fd450d 100644
--- a/Documentation/power/runtime_pm.rst
+++ b/Documentation/power/runtime_pm.rst

@@ -827,6 +827,14 @@ or driver about runtime power changes.  Instead, the driver for the device's
 parent must take responsibility for telling the device's driver when the
 parent's power state changes.

+Note that, in some cases it may not be desirable for subsystems/drivers to call

More than 80 chars.

Perhaps it's the email client that messes up the patch in some way.
This above line in the patch is 79 chars.

If you have a look at the patch in patchwork [1], you should see (I
hope) that it respects the 80 chars per line!?

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+pm_runtime_no_callbacks() for their devices. This could be because a subset of

More than 80 chars.

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+the runtime PM callbacks needs to be implemented, a platform dependent PM
+domain could get attached to the device or that the device is power manged

s/manged/managed/

Thanks for spotting this, my spell checker accepted "manged". :-)

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+through a supplier device link. For these reasons and to avoid boilerplate code

More than 80 chars.

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+in subsystems/drivers, the PM core allows runtime PM callbacks to be
+unassigned.
+

You should also mention that if a callback pointer is NULL, the
runtime PM core will act as though there was a callback and it
returned 0.  That's an important consideration.

Good point, let me add it.

I send a new version of $subject patch, unless Rafael is happy to do
the amending when/if applying?

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Also, notice that this file was carefully edited to make sure that
none of the lines exceed 80 characters.  Your new addition should
be the same.

Absolutely, but it should be okay already, no?

See above.

Alan

Kind regards
Uffe

[1]
https://patchwork.kernel.org/project/linux-pm/patch/20210608090250.85256-4-ulf.hansson@linaro.org/