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Date: Tue, 14 Jul 2015 15:19:16 +0200
From: Tomeu Vizoso <tomeu.vizoso@...labora.com>
To: Alan Stern <stern@...land.harvard.edu>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
"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 8 July 2015 at 22:31, Alan Stern <stern@...land.harvard.edu> wrote:
> 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.
Yeah, I think this is an improvement. Will give it a try.
>> 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.
Will this patch be picked up as-is or should I add it to my series
with a proper changelog?
Thanks,
Tomeu
> 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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