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Message-ID: <Pine.LNX.4.44L0.1507081617200.2243-100000@iolanthe.rowland.org>
Date: Wed, 8 Jul 2015 16:31:41 -0400 (EDT)
From: Alan Stern <stern@...land.harvard.edu>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
cc: Tomeu Vizoso <tomeu.vizoso@...labora.com>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Ulf Hansson <ulf.hansson@...aro.org>,
Kevin Hilman <khilman@...aro.org>,
Russell King <rmk+kernel@....linux.org.uk>,
Krzysztof Kozlowski <k.kozlowski@...sung.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive
On Wed, 8 Jul 2015, Rafael J. Wysocki wrote:
> I seem to have lost the context here, sorry about that.
>
> The idea seems to be to rely on the fact that the RPM status for all devices
> is initially RPM_SUSPENDED and that never changes if runtime PM is never
> enabled for the device, so in that particular case it would be OK to treat
> the "power.direct_complete set + RPM status == RPM_SUSPENDED" combination
> as valid even though runtime PM has never been enabled for the device in
> question (provided that power.direct_complete will never be set for "real"
> devices that don't support runtime PM). Is that correct?
I would have expressed it slightly differently, but yes, that's correct.
> That seems to be fragile, but I have no strong opinion.
In itself it's not all that bad, I think. In the presence of Tomeu's
new direct_complete_default flag, however, it does seem quite fragile.
We may want to do the direct_complete_default thing in a different way.
For example, the PM core could automatically set the direct_complete
flag if a device has _none_ of the system suspend callbacks (i.e., no
prepare, suspend, suspend_late, suspend_noirq, resume_noirq,
resume_early, resume, or complete). Although it would be a little
awkward to check this, it would be safer than inheriting
direct_complete_default from the parent and it ought to solve Tomeu's
problem just as well.
> Let's do that change if it allows us to make forward progress here. Please
> feel free to submit a documentation patch along the lines you've suggested.
Here's a proposed patch to illustrate what I have in mind. Since it
removes the only usage of pm_runtime_suspended_if_enabled(), it also
removes the definition of that function.
Alan Stern
Index: usb-4.1/drivers/base/power/main.c
===================================================================
--- usb-4.1.orig/drivers/base/power/main.c
+++ usb-4.1/drivers/base/power/main.c
@@ -1374,7 +1374,7 @@ static int __device_suspend(struct devic
if (dev->power.direct_complete) {
if (pm_runtime_status_suspended(dev)) {
pm_runtime_disable(dev);
- if (pm_runtime_suspended_if_enabled(dev))
+ if (pm_runtime_status_suspended(dev))
goto Complete;
pm_runtime_enable(dev);
Index: usb-4.1/Documentation/power/devices.txt
===================================================================
--- usb-4.1.orig/Documentation/power/devices.txt
+++ usb-4.1/Documentation/power/devices.txt
@@ -341,6 +341,13 @@ the phases are:
and is entirely responsible for bringing the device back to the
functional state as appropriate.
+ Note that this direct-complete procedure applies even if the device is
+ disabled for runtime PM; only the runtime-PM status matters. It follows
+ that if a device has system-sleep callbacks but does not support runtime
+ PM, then its prepare callback must never return a positive value. This
+ is because all devices are initially set to runtime-suspended with
+ runtime PM disabled.
+
2. The suspend methods should quiesce the device to stop it from performing
I/O. They also may save the device registers and put it into the
appropriate low-power state, depending on the bus type the device is on,
Index: usb-4.1/Documentation/power/runtime_pm.txt
===================================================================
--- usb-4.1.orig/Documentation/power/runtime_pm.txt
+++ usb-4.1/Documentation/power/runtime_pm.txt
@@ -445,10 +445,6 @@ drivers/base/power/runtime.c and include
bool pm_runtime_status_suspended(struct device *dev);
- return true if the device's runtime PM status is 'suspended'
- bool pm_runtime_suspended_if_enabled(struct device *dev);
- - return true if the device's runtime PM status is 'suspended' and its
- 'power.disable_depth' field is equal to 1
-
void pm_runtime_allow(struct device *dev);
- set the power.runtime_auto flag for the device and decrease its usage
counter (used by the /sys/devices/.../power/control interface to
Index: usb-4.1/include/linux/pm_runtime.h
===================================================================
--- usb-4.1.orig/include/linux/pm_runtime.h
+++ usb-4.1/include/linux/pm_runtime.h
@@ -98,11 +98,6 @@ static inline bool pm_runtime_status_sus
return dev->power.runtime_status == RPM_SUSPENDED;
}
-static inline bool pm_runtime_suspended_if_enabled(struct device *dev)
-{
- return pm_runtime_status_suspended(dev) && dev->power.disable_depth == 1;
-}
-
static inline bool pm_runtime_enabled(struct device *dev)
{
return !dev->power.disable_depth;
@@ -164,7 +159,6 @@ static inline void device_set_run_wake(s
static inline bool pm_runtime_suspended(struct device *dev) { return false; }
static inline bool pm_runtime_active(struct device *dev) { return true; }
static inline bool pm_runtime_status_suspended(struct device *dev) { return false; }
-static inline bool pm_runtime_suspended_if_enabled(struct device *dev) { return false; }
static inline bool pm_runtime_enabled(struct device *dev) { return false; }
static inline void pm_runtime_no_callbacks(struct device *dev) {}
--
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