[PATCH] devfreq: Suspend all devices on system shutdown

[PATCH] devfreq: Suspend all devices on system shutdown

[Marek Szyprowski]

This way devfreq core ensures that all its devices will be set to safe
operation points before reboot operation. There are board on which some
aggressive power saving operation points are behind the capabilities of
the bootloader to properly reset the hardware and boot the board. This
way one can avoid board crash early after reboot.

Similar pattern is used in CPUfreq subsystem.

Reported-by: Markus Reichl <m.reichl@fivetechno.de>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
 drivers/devfreq/devfreq.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 0ae3de76833b..f6aba8344c56 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -23,6 +23,7 @@
 #include <linux/devfreq.h>
 #include <linux/workqueue.h>
 #include <linux/platform_device.h>
+#include <linux/syscore_ops.h>
 #include <linux/list.h>
 #include <linux/printk.h>
 #include <linux/hrtimer.h>
@@ -1422,6 +1423,10 @@ static struct attribute *devfreq_attrs[] = {
 };
 ATTRIBUTE_GROUPS(devfreq);
 
+static struct syscore_ops devfreq_syscore_ops = {
+	.shutdown = devfreq_suspend,
+};
+
 static int __init devfreq_init(void)
 {
 	devfreq_class = class_create(THIS_MODULE, "devfreq");
@@ -1438,6 +1443,8 @@ static int __init devfreq_init(void)
 	}
 	devfreq_class->dev_groups = devfreq_groups;
 
+	register_syscore_ops(&devfreq_syscore_ops);
+
 	return 0;
 }
 subsys_initcall(devfreq_init);
-- 
2.17.1

Re: [PATCH] devfreq: Suspend all devices on system shutdown

[Chanwoo Choi]

Hi,

On 19. 1. 25. 오후 10:54, Marek Szyprowski wrote:
> This way devfreq core ensures that all its devices will be set to safe
> operation points before reboot operation. There are board on which some
> aggressive power saving operation points are behind the capabilities of
> the bootloader to properly reset the hardware and boot the board. This
> way one can avoid board crash early after reboot.
> 
> Similar pattern is used in CPUfreq subsystem.
> 
> Reported-by: Markus Reichl <m.reichl@fivetechno.de>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>  drivers/devfreq/devfreq.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 0ae3de76833b..f6aba8344c56 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -23,6 +23,7 @@
>  #include <linux/devfreq.h>
>  #include <linux/workqueue.h>
>  #include <linux/platform_device.h>
> +#include <linux/syscore_ops.h>
>  #include <linux/list.h>
>  #include <linux/printk.h>
>  #include <linux/hrtimer.h>
> @@ -1422,6 +1423,10 @@ static struct attribute *devfreq_attrs[] = {
>  };
>  ATTRIBUTE_GROUPS(devfreq);
>  
> +static struct syscore_ops devfreq_syscore_ops = {
> +	.shutdown = devfreq_suspend,
> +};
> +
>  static int __init devfreq_init(void)
>  {
>  	devfreq_class = class_create(THIS_MODULE, "devfreq");
> @@ -1438,6 +1443,8 @@ static int __init devfreq_init(void)
>  	}
>  	devfreq_class->dev_groups = devfreq_groups;
>  
> +	register_syscore_ops(&devfreq_syscore_ops);
> +
>  	return 0;
>  }
>  subsys_initcall(devfreq_init);
> 

Looks good to me.
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

RE: [PATCH] devfreq: Suspend all devices on system shutdown

[MyungJoo Ham]

>This way devfreq core ensures that all its devices will be set to safe
>operation points before reboot operation. There are board on which some
>aggressive power saving operation points are behind the capabilities of
>the bootloader to properly reset the hardware and boot the board. This
>way one can avoid board crash early after reboot.
>
>Similar pattern is used in CPUfreq subsystem.
>
>Reported-by: Markus Reichl <m.reichl@fivetechno.de>
>Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>---

You are invoking ALL devfreq suspend callbacks at shutdown
with this commit.

Can you make it invoke only devices explicitly saying their needs
to handle "SHUTDOWN" event?

For example, we can add a flag at struct devfreq_dev_profile:
"uint32_t requirement"
, where
0x1: need to operate at the initial frequency for suspend
0x2: need to operate at the initial frequency for shutdown
0x4: it forgets its status at resume, reconfigure frequency at resume.
(or reverse 0x1's semantics for the backward compatibility)
...

Cheers,
MyungJoo

Re: [PATCH] devfreq: Suspend all devices on system shutdown

[Marek Szyprowski]

Hi MyungJoo,

On 2019-01-28 09:05, MyungJoo Ham wrote:
>> This way devfreq core ensures that all its devices will be set to safe
>> operation points before reboot operation. There are board on which some
>> aggressive power saving operation points are behind the capabilities of
>> the bootloader to properly reset the hardware and boot the board. This
>> way one can avoid board crash early after reboot.
>>
>> Similar pattern is used in CPUfreq subsystem.
>>
>> Reported-by: Markus Reichl <m.reichl@fivetechno.de>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>> ---
> You are invoking ALL devfreq suspend callbacks at shutdown
> with this commit.
>
> Can you make it invoke only devices explicitly saying their needs
> to handle "SHUTDOWN" event?
>
> For example, we can add a flag at struct devfreq_dev_profile:
> "uint32_t requirement"
> , where
> 0x1: need to operate at the initial frequency for suspend
> 0x2: need to operate at the initial frequency for shutdown
> 0x4: it forgets its status at resume, reconfigure frequency at resume.
> (or reverse 0x1's semantics for the backward compatibility)

Frankly speaking this looks like an over-engineering. Switching to safe
frequency during reboot shouldn't have any negative side-effects. IMHO
such flags can be always added later, once there will be a real use case
for them.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [PATCH] devfreq: Suspend all devices on system shutdown

[Pavel Machek]

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On Fri 2019-01-25 14:54:03, Marek Szyprowski wrote:
> This way devfreq core ensures that all its devices will be set to safe
> operation points before reboot operation. There are board on which some
> aggressive power saving operation points are behind the capabilities of
> the bootloader to properly reset the hardware and boot the board. This
> way one can avoid board crash early after reboot.
> 
> Similar pattern is used in CPUfreq subsystem.

This looks somehow dangerous to me. I guess this will break someone's
shutdown, and on battery-powered devices, that's quite bad thing to
do.

Could we explicitely do it only for devices that need it?
								Pavel
								
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Re: [PATCH] devfreq: Suspend all devices on system shutdown

[Chanwoo Choi]

Hi Pavel,

On 19. 3. 7. 오전 8:10, Pavel Machek wrote:
> On Fri 2019-01-25 14:54:03, Marek Szyprowski wrote:
>> This way devfreq core ensures that all its devices will be set to safe
>> operation points before reboot operation. There are board on which some
>> aggressive power saving operation points are behind the capabilities of
>> the bootloader to properly reset the hardware and boot the board. This
>> way one can avoid board crash early after reboot.
>>
>> Similar pattern is used in CPUfreq subsystem.
> 
> This looks somehow dangerous to me. I guess this will break someone's
> shutdown, and on battery-powered devices, that's quite bad thing to
> do.

This patch executes the devfreq_suspend() for all devfreq devices.
The devfreq_suspend() does the following:
	1. (mandatory) stop the polling of governor.
	2. (optional)  If devfreq device specifies the 'opp-suspend'
	property in DT, the devfreq changes the frequency by using
	the devfreq->suspend_freq.

If the user of devfreq device doesn't want to change the frequency
during the system shutdown, just don't add the 'opp-suspend' property
in DT. And the devfreq_suspend() will just stop the polling for governor.

Even if on battery-powered devices, I think it is not problem
to stop the polling of governor during the system shutdown.

In my case, I don't know what is dangerous.
Could you explain it more detailed.

> 
> Could we explicitely do it only for devices that need it?
> 								Pavel
> 								
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics