[RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Zoran Markovic]

From: Benoit Goby <benoit@android.com>

Rather than hard-lock the kernel, dump the suspend/resume thread stack and
panic() to capture a message in pstore when a driver takes too long to
suspend/resume. Default suspend/resume watchdog timeout is set to 12
seconds to be longer than the usbhid 10 second timeout, but could be
changed at compile time.

Exclude from the watchdog the time spent waiting for children that
are resumed asynchronously and time every device, whether or not they
resumed synchronously.

This patch is targeted for mobile devices where a suspend/resume lockup
could cause a system reboot. Information about failing device can be
retrieved in subsequent boot session by mounting pstore and inspecting
the log.

The hardware watchdog timer is likely suspended during this time and
couldn't be relied upon. The soft-lockup detector would eventually tell
that tasks are not scheduled, but would provide little context as to why.
The patch hence uses system timer and assumes it is still active while the
devices are suspended/resumed.

This feature can be enabled/disabled during kernel configuration.

Cc: Android Kernel Team <kernel-team@android.com>
Cc: Colin Cross <ccross@android.com>
Cc: Todd Poynor <toddpoynor@google.com>
Cc: San Mehat <san@google.com>
Cc: Benoit Goby <benoit@android.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Len Brown <len.brown@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Original-author: San Mehat <san@google.com>
Signed-off-by: Benoit Goby <benoit@android.com>
[zoran.markovic@linaro.org: Changed printk(KERN_EMERG,...) to pr_emerg(...),
tweaked commit message. Minor changes to add compile-time inclusion of
the feature.]
Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org>
---
v3: 
* Added explicit dependency on pstore
* Collapsed recovery options to system panic only
* Logged driver string in panic message

 drivers/base/power/main.c |   70 +++++++++++++++++++++++++++++++++++++++++++++
 kernel/power/Kconfig      |   16 +++++++++++
 2 files changed, 86 insertions(+)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 5a9b656..c19aec0 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -29,6 +29,8 @@
 #include <linux/async.h>
 #include <linux/suspend.h>
 #include <linux/cpuidle.h>
+#include <linux/timer.h>
+
 #include "../base.h"
 #include "power.h"
 
@@ -54,6 +56,12 @@ struct suspend_stats suspend_stats;
 static DEFINE_MUTEX(dpm_list_mtx);
 static pm_message_t pm_transition;
 
+struct dpm_watchdog {
+	struct device		*dev;
+	struct task_struct	*tsk;
+	struct timer_list	timer;
+};
+
 static int async_error;
 
 /**
@@ -384,6 +392,60 @@ static int dpm_run_callback(pm_callback_t cb, struct device *dev,
 	return error;
 }
 
+#ifdef CONFIG_DPM_WD
+/**
+ * dpm_wd_handler - Driver suspend / resume watchdog handler.
+ *
+ * Called when a driver has timed out suspending or resuming.
+ * There's not much we can do here to recover so panic() to
+ * capture a crash-dump in pstore.
+ */
+static void dpm_wd_handler(unsigned long data)
+{
+	struct dpm_watchdog *wd = (void *)data;
+
+	dev_emerg(wd->dev, "**** DPM device timeout ****\n");
+	show_stack(wd->tsk, NULL);
+	panic("%s %s: unrecoverable failure\n",
+		dev_driver_string(wd->dev), dev_name(wd->dev));
+}
+
+/**
+ * dpm_wd_set - Enable pm watchdog for given device.
+ * @wd: Watchdog. Must be allocated on the stack.
+ * @dev: Device to handle.
+ */
+static void dpm_wd_set(struct dpm_watchdog *wd, struct device *dev)
+{
+	struct timer_list *timer = &wd->timer;
+
+	wd->dev = dev;
+	wd->tsk = get_current();
+
+	init_timer_on_stack(timer);
+	/* use same timeout value for both suspend and resume */
+	timer->expires = jiffies + HZ * CONFIG_DPM_WD_TIMEOUT;
+	timer->function = dpm_wd_handler;
+	timer->data = (unsigned long)wd;
+	add_timer(timer);
+}
+
+/**
+ * dpm_wd_clear - Disable suspend/resume watchdog.
+ * @wd: Watchdog to disable.
+ */
+static void dpm_wd_clear(struct dpm_watchdog *wd)
+{
+	struct timer_list *timer = &wd->timer;
+
+	del_timer_sync(timer);
+	destroy_timer_on_stack(timer);
+}
+#else
+#define dpm_wd_set(x, y)
+#define dpm_wd_clear(x)
+#endif
+
 /*------------------------- Resume routines -------------------------*/
 
 /**
@@ -570,6 +632,7 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
 	pm_callback_t callback = NULL;
 	char *info = NULL;
 	int error = 0;
+	struct dpm_watchdog wd;
 
 	TRACE_DEVICE(dev);
 	TRACE_RESUME(0);
@@ -585,6 +648,7 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
 	 * a resumed device, even if the device hasn't been completed yet.
 	 */
 	dev->power.is_prepared = false;
+	dpm_wd_set(&wd, dev);
 
 	if (!dev->power.is_suspended)
 		goto Unlock;
@@ -636,6 +700,7 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
 
  Unlock:
 	device_unlock(dev);
+	dpm_wd_clear(&wd);
 
  Complete:
 	complete_all(&dev->power.completion);
@@ -1053,6 +1118,7 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
 	pm_callback_t callback = NULL;
 	char *info = NULL;
 	int error = 0;
+	struct dpm_watchdog wd;
 
 	dpm_wait_for_children(dev, async);
 
@@ -1076,6 +1142,8 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
 	if (dev->power.syscore)
 		goto Complete;
 
+	dpm_wd_set(&wd, dev);
+
 	device_lock(dev);
 
 	if (dev->pm_domain) {
@@ -1131,6 +1199,8 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
 
 	device_unlock(dev);
 
+	dpm_wd_clear(&wd);
+
  Complete:
 	complete_all(&dev->power.completion);
 	if (error)
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index d444c4e..6a6b763 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -178,6 +178,22 @@ config PM_SLEEP_DEBUG
 	def_bool y
 	depends on PM_DEBUG && PM_SLEEP
 
+config DPM_WD
+	bool "Device suspend/resume watchdog"
+	depends on PM_DEBUG && PSTORE
+	---help---
+	  Sets up a watchdog timer to capture drivers that are
+	  locked up attempting to suspend/resume a device.
+	  A detected lockup causes system panic with message
+	  captured in pstore device for inspection in subsequent
+	  boot session.
+
+config DPM_WD_TIMEOUT
+	int "Watchdog timeout in seconds"
+	range 1 120
+	default 12
+	depends on DPM_WD
+
 config PM_TRACE
 	bool
 	help
-- 
1.7.9.5

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Zoran Markovic]

Rafael,
I haven't seen any other proposals/alternatives on how to do this. Is
there anything else we should do to get this upstream? I believe this
is a valuable debug feature for Android and it now explicitly depends
on pstore...
Thanks,
Zoran

On 30 July 2013 13:38, Zoran Markovic <zoran.markovic@linaro.org> wrote:
> From: Benoit Goby <benoit@android.com>
>
> Rather than hard-lock the kernel, dump the suspend/resume thread stack and
> panic() to capture a message in pstore when a driver takes too long to
> suspend/resume. Default suspend/resume watchdog timeout is set to 12
> seconds to be longer than the usbhid 10 second timeout, but could be
> changed at compile time.
>
> Exclude from the watchdog the time spent waiting for children that
> are resumed asynchronously and time every device, whether or not they
> resumed synchronously.
>
> This patch is targeted for mobile devices where a suspend/resume lockup
> could cause a system reboot. Information about failing device can be
> retrieved in subsequent boot session by mounting pstore and inspecting
> the log.
>
> The hardware watchdog timer is likely suspended during this time and
> couldn't be relied upon. The soft-lockup detector would eventually tell
> that tasks are not scheduled, but would provide little context as to why.
> The patch hence uses system timer and assumes it is still active while the
> devices are suspended/resumed.
>
> This feature can be enabled/disabled during kernel configuration.
>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Todd Poynor <toddpoynor@google.com>
> Cc: San Mehat <san@google.com>
> Cc: Benoit Goby <benoit@android.com>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Pavel Machek <pavel@ucw.cz>
> Cc: Rafael J. Wysocki <rjw@sisk.pl>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Original-author: San Mehat <san@google.com>
> Signed-off-by: Benoit Goby <benoit@android.com>
> [zoran.markovic@linaro.org: Changed printk(KERN_EMERG,...) to pr_emerg(...),
> tweaked commit message. Minor changes to add compile-time inclusion of
> the feature.]
> Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org>
> ---
> v3:
> * Added explicit dependency on pstore
> * Collapsed recovery options to system panic only
> * Logged driver string in panic message
>
>  drivers/base/power/main.c |   70 +++++++++++++++++++++++++++++++++++++++++++++
>  kernel/power/Kconfig      |   16 +++++++++++
>  2 files changed, 86 insertions(+)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 5a9b656..c19aec0 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -29,6 +29,8 @@
>  #include <linux/async.h>
>  #include <linux/suspend.h>
>  #include <linux/cpuidle.h>
> +#include <linux/timer.h>
> +
>  #include "../base.h"
>  #include "power.h"
>
> @@ -54,6 +56,12 @@ struct suspend_stats suspend_stats;
>  static DEFINE_MUTEX(dpm_list_mtx);
>  static pm_message_t pm_transition;
>
> +struct dpm_watchdog {
> +       struct device           *dev;
> +       struct task_struct      *tsk;
> +       struct timer_list       timer;
> +};
> +
>  static int async_error;
>
>  /**
> @@ -384,6 +392,60 @@ static int dpm_run_callback(pm_callback_t cb, struct device *dev,
>         return error;
>  }
>
> +#ifdef CONFIG_DPM_WD
> +/**
> + * dpm_wd_handler - Driver suspend / resume watchdog handler.
> + *
> + * Called when a driver has timed out suspending or resuming.
> + * There's not much we can do here to recover so panic() to
> + * capture a crash-dump in pstore.
> + */
> +static void dpm_wd_handler(unsigned long data)
> +{
> +       struct dpm_watchdog *wd = (void *)data;
> +
> +       dev_emerg(wd->dev, "**** DPM device timeout ****\n");
> +       show_stack(wd->tsk, NULL);
> +       panic("%s %s: unrecoverable failure\n",
> +               dev_driver_string(wd->dev), dev_name(wd->dev));
> +}
> +
> +/**
> + * dpm_wd_set - Enable pm watchdog for given device.
> + * @wd: Watchdog. Must be allocated on the stack.
> + * @dev: Device to handle.
> + */
> +static void dpm_wd_set(struct dpm_watchdog *wd, struct device *dev)
> +{
> +       struct timer_list *timer = &wd->timer;
> +
> +       wd->dev = dev;
> +       wd->tsk = get_current();
> +
> +       init_timer_on_stack(timer);
> +       /* use same timeout value for both suspend and resume */
> +       timer->expires = jiffies + HZ * CONFIG_DPM_WD_TIMEOUT;
> +       timer->function = dpm_wd_handler;
> +       timer->data = (unsigned long)wd;
> +       add_timer(timer);
> +}
> +
> +/**
> + * dpm_wd_clear - Disable suspend/resume watchdog.
> + * @wd: Watchdog to disable.
> + */
> +static void dpm_wd_clear(struct dpm_watchdog *wd)
> +{
> +       struct timer_list *timer = &wd->timer;
> +
> +       del_timer_sync(timer);
> +       destroy_timer_on_stack(timer);
> +}
> +#else
> +#define dpm_wd_set(x, y)
> +#define dpm_wd_clear(x)
> +#endif
> +
>  /*------------------------- Resume routines -------------------------*/
>
>  /**
> @@ -570,6 +632,7 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
>         pm_callback_t callback = NULL;
>         char *info = NULL;
>         int error = 0;
> +       struct dpm_watchdog wd;
>
>         TRACE_DEVICE(dev);
>         TRACE_RESUME(0);
> @@ -585,6 +648,7 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
>          * a resumed device, even if the device hasn't been completed yet.
>          */
>         dev->power.is_prepared = false;
> +       dpm_wd_set(&wd, dev);
>
>         if (!dev->power.is_suspended)
>                 goto Unlock;
> @@ -636,6 +700,7 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
>
>   Unlock:
>         device_unlock(dev);
> +       dpm_wd_clear(&wd);
>
>   Complete:
>         complete_all(&dev->power.completion);
> @@ -1053,6 +1118,7 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
>         pm_callback_t callback = NULL;
>         char *info = NULL;
>         int error = 0;
> +       struct dpm_watchdog wd;
>
>         dpm_wait_for_children(dev, async);
>
> @@ -1076,6 +1142,8 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
>         if (dev->power.syscore)
>                 goto Complete;
>
> +       dpm_wd_set(&wd, dev);
> +
>         device_lock(dev);
>
>         if (dev->pm_domain) {
> @@ -1131,6 +1199,8 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
>
>         device_unlock(dev);
>
> +       dpm_wd_clear(&wd);
> +
>   Complete:
>         complete_all(&dev->power.completion);
>         if (error)
> diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
> index d444c4e..6a6b763 100644
> --- a/kernel/power/Kconfig
> +++ b/kernel/power/Kconfig
> @@ -178,6 +178,22 @@ config PM_SLEEP_DEBUG
>         def_bool y
>         depends on PM_DEBUG && PM_SLEEP
>
> +config DPM_WD
> +       bool "Device suspend/resume watchdog"
> +       depends on PM_DEBUG && PSTORE
> +       ---help---
> +         Sets up a watchdog timer to capture drivers that are
> +         locked up attempting to suspend/resume a device.
> +         A detected lockup causes system panic with message
> +         captured in pstore device for inspection in subsequent
> +         boot session.
> +
> +config DPM_WD_TIMEOUT
> +       int "Watchdog timeout in seconds"
> +       range 1 120
> +       default 12
> +       depends on DPM_WD
> +
>  config PM_TRACE
>         bool
>         help
> --
> 1.7.9.5
>

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Rafael J. Wysocki]

On Thursday, August 22, 2013 10:16:59 AM Zoran Markovic wrote:
> Rafael,
> I haven't seen any other proposals/alternatives on how to do this. Is
> there anything else we should do to get this upstream? I believe this
> is a valuable debug feature for Android and it now explicitly depends
> on pstore...

I haven't had a lot of time to look at this recently, sorry.

It doesn't look too bad from a quick look, but there's a couple of things
I don't like in it still (relatively minor).

I'll have a deeper look at it over the weekend (if nothing distracts me).

Thanks,
Rafael

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Zoran Markovic]

Hi Rafael,
> It doesn't look too bad from a quick look, but there's a couple of things
> I don't like in it still (relatively minor).

If there are things you would like changed in this patch, please let
me know. It would be nice to catch the 3.12 merge window.
Thanks,
- Zoran

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Rafael J. Wysocki]

On Wednesday, August 28, 2013 10:45:45 AM Zoran Markovic wrote:
> Hi Rafael,
> > It doesn't look too bad from a quick look, but there's a couple of things
> > I don't like in it still (relatively minor).
> 
> If there are things you would like changed in this patch, please let
> me know. It would be nice to catch the 3.12 merge window.

Well, it's not in my queue to be honest.

Is there any practical reason why it should go into the next release?

Rafael

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Zoran Markovic]

> Is there any practical reason why it should go into the next release?

Android folks find this useful, albeit a debug feature.

Zoran

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[John Stultz]

On 08/28/2013 01:52 PM, Rafael J. Wysocki wrote:
> On Wednesday, August 28, 2013 10:45:45 AM Zoran Markovic wrote:
>> Hi Rafael,
>>> It doesn't look too bad from a quick look, but there's a couple of things
>>> I don't like in it still (relatively minor).
>> If there are things you would like changed in this patch, please let
>> me know. It would be nice to catch the 3.12 merge window.
> Well, it's not in my queue to be honest.
>
> Is there any practical reason why it should go into the next release?

I wouldn't say its critical for the next release, but I feel like this
was the same response last cycle. Zoran's since investigated the various
alternative approaches you've suggested, and continues to be interested
in resolving your remaining objections.

Its a useful feature the Android devs use, which could also help
non-android developers debug suspend issues on their systems.

If you really just feel its something best left out of tree, that's hard
to argue against. Its just a debug tool and the android guys don't have
an issue carrying their own tree, after all. But the cost of leaving it
out is just the potential of others having to re-implement similar hacks
on their own instead of collaborating on shared infrastructure.

thanks
-john

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Colin Cross]

On Wed, Aug 28, 2013 at 3:36 PM, John Stultz <john.stultz@linaro.org> wrote:
> On 08/28/2013 01:52 PM, Rafael J. Wysocki wrote:
>> On Wednesday, August 28, 2013 10:45:45 AM Zoran Markovic wrote:
>>> Hi Rafael,
>>>> It doesn't look too bad from a quick look, but there's a couple of things
>>>> I don't like in it still (relatively minor).
>>> If there are things you would like changed in this patch, please let
>>> me know. It would be nice to catch the 3.12 merge window.
>> Well, it's not in my queue to be honest.
>>
>> Is there any practical reason why it should go into the next release?
>
> I wouldn't say its critical for the next release, but I feel like this
> was the same response last cycle. Zoran's since investigated the various
> alternative approaches you've suggested, and continues to be interested
> in resolving your remaining objections.
>
> Its a useful feature the Android devs use, which could also help
> non-android developers debug suspend issues on their systems.
>
> If you really just feel its something best left out of tree, that's hard
> to argue against. Its just a debug tool and the android guys don't have
> an issue carrying their own tree, after all. But the cost of leaving it
> out is just the potential of others having to re-implement similar hacks
> on their own instead of collaborating on shared infrastructure.

And the benefit is that you are more likely to get bugreports that
have a stack trace of the offending suspend callback instead of "my
laptop doesn't suspend any more".

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Rafael J. Wysocki]

On Wednesday, August 28, 2013 03:43:42 PM Colin Cross wrote:
> On Wed, Aug 28, 2013 at 3:36 PM, John Stultz <john.stultz@linaro.org> wrote:
> > On 08/28/2013 01:52 PM, Rafael J. Wysocki wrote:
> >> On Wednesday, August 28, 2013 10:45:45 AM Zoran Markovic wrote:
> >>> Hi Rafael,
> >>>> It doesn't look too bad from a quick look, but there's a couple of things
> >>>> I don't like in it still (relatively minor).
> >>> If there are things you would like changed in this patch, please let
> >>> me know. It would be nice to catch the 3.12 merge window.
> >> Well, it's not in my queue to be honest.
> >>
> >> Is there any practical reason why it should go into the next release?
> >
> > I wouldn't say its critical for the next release, but I feel like this
> > was the same response last cycle. Zoran's since investigated the various
> > alternative approaches you've suggested, and continues to be interested
> > in resolving your remaining objections.
> >
> > Its a useful feature the Android devs use, which could also help
> > non-android developers debug suspend issues on their systems.
> >
> > If you really just feel its something best left out of tree, that's hard
> > to argue against. Its just a debug tool and the android guys don't have
> > an issue carrying their own tree, after all. But the cost of leaving it
> > out is just the potential of others having to re-implement similar hacks
> > on their own instead of collaborating on shared infrastructure.

Well, let's just say it had a bad luck timing-wise this time.

It's still there in my todo list and I'll take care of it eventually, but not
today and not tomorrow, which basically is what you're asking for.

> And the benefit is that you are more likely to get bugreports that
> have a stack trace of the offending suspend callback instead of "my
> laptop doesn't suspend any more".

Yes, I understand that.

Thanks,
Rafael

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[Pavel Machek]

On Wed 2013-08-28 15:43:42, Colin Cross wrote:
> On Wed, Aug 28, 2013 at 3:36 PM, John Stultz <john.stultz@linaro.org> wrote:
> > On 08/28/2013 01:52 PM, Rafael J. Wysocki wrote:
> >> On Wednesday, August 28, 2013 10:45:45 AM Zoran Markovic wrote:
> >>> Hi Rafael,
> >>>> It doesn't look too bad from a quick look, but there's a couple of things
> >>>> I don't like in it still (relatively minor).
> >>> If there are things you would like changed in this patch, please let
> >>> me know. It would be nice to catch the 3.12 merge window.
> >> Well, it's not in my queue to be honest.
> >>
> >> Is there any practical reason why it should go into the next release?
> >
> > I wouldn't say its critical for the next release, but I feel like this
> > was the same response last cycle. Zoran's since investigated the various
> > alternative approaches you've suggested, and continues to be interested
> > in resolving your remaining objections.
> >
> > Its a useful feature the Android devs use, which could also help
> > non-android developers debug suspend issues on their systems.
> >
> > If you really just feel its something best left out of tree, that's hard
> > to argue against. Its just a debug tool and the android guys don't have
> > an issue carrying their own tree, after all. But the cost of leaving it
> > out is just the potential of others having to re-implement similar hacks
> > on their own instead of collaborating on shared infrastructure.
> 
> And the benefit is that you are more likely to get bugreports that
> have a stack trace of the offending suspend callback instead of "my
> laptop doesn't suspend any more".

Laptops do not have persistent store for dmesg. So... are you sure?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [RFC PATCHv3] drivers: power: Detect device suspend/resume lockup and log event in pstore.

[John Stultz]

On 08/29/2013 11:23 AM, Pavel Machek wrote:
> On Wed 2013-08-28 15:43:42, Colin Cross wrote:
>> On Wed, Aug 28, 2013 at 3:36 PM, John Stultz <john.stultz@linaro.org> wrote:
>>> On 08/28/2013 01:52 PM, Rafael J. Wysocki wrote:
>>>> On Wednesday, August 28, 2013 10:45:45 AM Zoran Markovic wrote:
>>>>> Hi Rafael,
>>>>>> It doesn't look too bad from a quick look, but there's a couple of things
>>>>>> I don't like in it still (relatively minor).
>>>>> If there are things you would like changed in this patch, please let
>>>>> me know. It would be nice to catch the 3.12 merge window.
>>>> Well, it's not in my queue to be honest.
>>>>
>>>> Is there any practical reason why it should go into the next release?
>>> I wouldn't say its critical for the next release, but I feel like this
>>> was the same response last cycle. Zoran's since investigated the various
>>> alternative approaches you've suggested, and continues to be interested
>>> in resolving your remaining objections.
>>>
>>> Its a useful feature the Android devs use, which could also help
>>> non-android developers debug suspend issues on their systems.
>>>
>>> If you really just feel its something best left out of tree, that's hard
>>> to argue against. Its just a debug tool and the android guys don't have
>>> an issue carrying their own tree, after all. But the cost of leaving it
>>> out is just the potential of others having to re-implement similar hacks
>>> on their own instead of collaborating on shared infrastructure.
>> And the benefit is that you are more likely to get bugreports that
>> have a stack trace of the offending suspend callback instead of "my
>> laptop doesn't suspend any more".
> Laptops do not have persistent store for dmesg. So... are you sure?

I pstore has support for EFI, so some laptops do.

thanks
-john