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Date: Thu, 14 May 2015 21:56:18 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc: linux-pm@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Kevin Hilman <khilman@...nel.org>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PM / sleep: Let devices force direct_complete
On Thursday, May 14, 2015 03:37:52 PM Tomeu Vizoso wrote:
> Introduce a new per-device flag power.force_direct_complete that will
> instruct the PM core to let that device remain in runtime suspend when
> the system goes into a sleep power state, regardless of the PM state of
> any of its descendants.
>
> This is needed because otherwise it would be needed to get dozens of
> drivers to implement the prepare() callback and be runtime PM active
> even if they don't have a 1-to-1 relationship with a piece of HW.
>
> This only applies to devices that aren't wakeup-capable, as those would
> need to setup their IRQs as wakeup-capable in their prepare() callbacks.
>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
Well, my idea of a "direct complete" flag was a bit different and I have
a concern with this particular implementation. ->
>
> ---
>
> v2: * Fix wording as suggested by Kevin Hilman
> ---
> Documentation/power/runtime_pm.txt | 10 ++++++++++
> drivers/base/power/main.c | 14 ++++++++++----
> include/linux/pm.h | 1 +
> 3 files changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
> index 44fe1d2..e131aab 100644
> --- a/Documentation/power/runtime_pm.txt
> +++ b/Documentation/power/runtime_pm.txt
> @@ -665,6 +665,16 @@ as appropriate. This only applies to system suspend transitions that are not
> related to hibernation (see Documentation/power/devices.txt for more
> information).
>
> +For devices that know they can remain runtime suspended when the system
> +transitions to a sleep state regardless of the PM state of their descendants,
> +the flag power.force_direct_complete can be set on their device structures.
> +This can be useful when a real device has several virtual devices as
> +descendants and it would be very cumbersome to make sure that they return a
> +positive value in their .prepare() callback and have runtime PM enabled. Usage
> +of power.force_direct_complete is only allowed to devices that aren't
> +wakeup-capable, as they would need to set their IRQs as wakeups in their
> +.prepare() callbacks before the system transitions to a sleep state.
> +
> The PM core does its best to reduce the probability of race conditions between
> the runtime PM and system suspend/resume (and hibernation) callbacks by carrying
> out the following operations:
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 3d874ec..7b962f5 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -1438,7 +1438,9 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
> if (parent) {
> spin_lock_irq(&parent->power.lock);
>
> - dev->parent->power.direct_complete = false;
> + if (!dev->parent->power.force_direct_complete)
> + dev->parent->power.direct_complete = false;
> +
> if (dev->power.wakeup_path
> && !dev->parent->power.ignore_children)
> dev->parent->power.wakeup_path = true;
> @@ -1605,9 +1607,13 @@ static int device_prepare(struct device *dev, pm_message_t state)
> * will do the same thing with all of its descendants". This only
> * applies to suspend transitions, however.
> */
> - spin_lock_irq(&dev->power.lock);
> - dev->power.direct_complete = ret > 0 && state.event == PM_EVENT_SUSPEND;
> - spin_unlock_irq(&dev->power.lock);
> + if (state.event == PM_EVENT_SUSPEND) {
> + spin_lock_irq(&dev->power.lock);
> + dev->power.direct_complete = ret > 0 ||
> + (dev->power.force_direct_complete &&
> + !device_can_wakeup(dev));
-> What if the bus type (or PM domain) has a good reason to not return a positive
number from ->prepare even though the driver thinks it would be OK to do that?
The changes here would break that case I think, wouldn't they?
I thought about adding a flag that would work if the ->prepare callback was
not present. So device_prepare() would check that flag for NULL 'callback'
only and then it would set 'ret' to 1 if the flag was set.
Something like in the (untested) patch below.
Wouldn't that be sufficient to cover the use cases you care about?
> + spin_unlock_irq(&dev->power.lock);
> + }
> return 0;
> }
>
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index 2d29c64..2e41cfd 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -553,6 +553,7 @@ struct dev_pm_info {
> bool ignore_children:1;
> bool early_init:1; /* Owned by the PM core */
> bool direct_complete:1; /* Owned by the PM core */
> + bool force_direct_complete:1;
> spinlock_t lock;
> #ifdef CONFIG_PM_SLEEP
> struct list_head entry;
>
---
drivers/base/power/main.c | 2 ++
include/linux/pm.h | 1 +
2 files changed, 3 insertions(+)
Index: linux-pm/drivers/base/power/main.c
===================================================================
--- linux-pm.orig/drivers/base/power/main.c
+++ linux-pm/drivers/base/power/main.c
@@ -1589,6 +1589,8 @@ static int device_prepare(struct device
trace_device_pm_callback_start(dev, info, state.event);
ret = callback(dev);
trace_device_pm_callback_end(dev, ret);
+ } else if (dev->power.direct_complete_default) {
+ ret = 1;
}
device_unlock(dev);
Index: linux-pm/include/linux/pm.h
===================================================================
--- linux-pm.orig/include/linux/pm.h
+++ linux-pm/include/linux/pm.h
@@ -553,6 +553,7 @@ struct dev_pm_info {
bool ignore_children:1;
bool early_init:1; /* Owned by the PM core */
bool direct_complete:1; /* Owned by the PM core */
+ bool direct_complete_default:1; /* Ditto */
spinlock_t lock;
#ifdef CONFIG_PM_SLEEP
struct list_head entry;
--
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