On Fri, 16 May 2014 23:08:01 +0200
"Rafael J. Wysocki" [off-list ref] wrote:

On Friday, May 16, 2014 08:20:55 AM Jacob Pan wrote:

quoted

On Thu, 15 May 2014 11:58:55 -0400 (EDT)
Alan Stern [off-list ref] wrote:

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On Thu, 15 May 2014, Jacob Pan wrote:

quoted

On Thu, 15 May 2014 10:29:42 -0400 (EDT)
Alan Stern [off-list ref] wrote:

quoted

On Thu, 15 May 2014, Jacob Pan wrote:

quoted

quoted

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should we respect ignore_children flag here? not all
parent devices create children with proper .prepare()
function. this allows parents override children.
I am looking at USB, a USB device could have logical
children such as ep_xx, they don't go through the same
subsystem .prepare().

Well, I'm not sure about that.  Let me consider that for a
while.

OK. let me be more clear about the situation i see in USB.
Correct me if I am wrong, a USB device will always has at
least one endpoint/ep_00 as a kid for control pipe, it is a
logical device. So when device_prepare() is called, its
call back is NULL which makes .direct_complete = 0. Since
children device suspend is called before parents, the
parents .direct_complete flag will always get cleared.

What i am trying to achieve here is to see if we avoid
resuming built-in (hardwired connect_type) non-hub USB
devices based on this new patchset. E.g. we don't want to
resume/suspend USB camera every time in system
suspend/resume cycle if they are already rpm suspended. We
can save ~100ms resume time for the devices we have tested.

This is a good point, but I don't think it is at all related
to ignore_children.

Instead, it seems that the best way to solve it would be to
add a ->prepare() handler for usb_ep_device_type that would
always turn on direct_complete.

yeah, that would solve the problem with EP device type. But what
about other subdevices. e.g. for USB camera, uvcvideo device? We
can add .prepare(return 1;) for each level but would it be
better to have a flag similar to ignore_children if not
ignore_children itself.

Something like that could always be added.

or, how about if a device's .prepare() is NULL, we could
assume .direct_resume() should be set. i.e.

You mean direct_complete (which is a flag, not a function), I suppose?

yes.

Wouldn't that go a bit too far?  It seems to be based on the
assumption that all devices having no ->prepare() callback can be
safely left in runtime suspend over a system suspend/resume cycle,
but is that assumption actually satisfied for all such devices?

yes, I agree it is risky though i don't see problems with my limited
testing. But on the other side, it is too strict.
I also tried adding .prepare( return 1;) to usb_ep_device_type pm ops,
that didn't work either. The reason is that ep devices don't support
runtime pm (disable_depth > 0). I think in this case ignore_children
flag should be the right indicator to ignore pm_runtime_suspended()?

quoted

--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c

@@ -1539,7 +1539,7 @@ static int device_prepare(struct device *dev,

pm_message_t state) pm_runtime_put(dev);
                return ret;
        }
-       dev->power.direct_complete = ret > 0 && state.event ==
PM_EVENT_SUSPEND
+       dev->power.direct_complete = (!callback || ret > 0) &&
state.event == PM_EVENT_SUSPEND && pm_runtime_suspended(dev);
        dev_dbg(dev, "%s:direct_complete %d, info %s\n", __func__,
dev->power.direct_complete, info);

quoted

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Actually, I don't understand why this is not related to
ignore_children. Could you explain?

It's hard to explain why two things are totally separate.  Much
better for you to describe why you think they _are_ related, so
that I can explain how you are wrong.

quoted

If the parent knows it can ignore children and already rpm
suspended, why do we still ask children?

The "ignore_children" flag doesn't mean that the parent can ignore
its children.  It means that the PM core is allowed to do a
runtime suspend of the parent while leaving the children at full
power.

In particular, it doesn't mean that the children's ->suspend()
callback will work correctly if it is called while the parent is
runtime suspended.

that explains my question about ignore_chilren flag. thanks.

quoted

Alan Stern

[Jacob Pan]
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[Jacob Pan]