Re: [linux-pm] [patch update] PM: Introduce core framework for run-time PM of I/O devices (rev. 5)

Alan Stern
2009-06-25T16:49:43Z

On Wed, 24 Jun 2009, Alan Stern wrote:
> More comments to follow when I get time to review more of the code...

Here we go. This isn't so detailed, because I wasn't able to do a
detailed review. Frankly, the code is kind of a mess.

The whole business about the runtime_notify and RPM_NOTIFY flags is
impenetrable. My suggestion: Rename runtime_notify to notify_pending
and eliminate RPM_NOTIFY. Then make sure that notify_pending is set
whenever a notify work item is queued.

The pm_notify_or_cancel_work routine should just be pm_notify_work.
It's silly to submit a workqueue item just to cancel a delayed
workqueue item! Do all the cancellations in the __pm_runtime_resume
and __pm_runtime_suspend routines, where you're already in process
context. If this means a work item occasionally runs at the wrong time
then let it -- it will quickly find out that it has nothing to do.
And while you're at it, get rid of the runtime_break flag.

The logic in __pm_runtime_resume and __pm_runtime_suspend is too
complicated to check. This is probably because of the interactions
with RPM_NOTIFY and runtime_break. Once they are gone, the logic
should be much more straightforward: test the flags, then do whatever
is needed based on the status.

I think once these cleanups are made, the code will be a lot more
transparent.

In __pm_runtime_resume, don't assume that incrementing the parent's
child_count will prevent the parent from suspending; also increment the
resume_count. And don't forget to decrement the parent's child_count
again if the resume fails.

In __pm_runtime_suspend, you should decrement the parent's child_count
before releasing the child's lock. The pm_runtime_idle call should
stay where it is, of course.

One more thing: Don't use flush_work or its relatives -- it tends to
cause deadlocks. Use cancel_work_sync instead.

Alan Stern