Discussion on device's runtime wake capability

-----Original Message-----
From: [email protected] [mailto:linux-acpi- [email protected]] On Behalf Of Aaron Lu
Sent: Tuesday, October 09, 2012 2:23 PM
To: Rafael J. Wysocki; Len Brown
Cc: Huang, Ying; Zhang, Rui; [email protected]
Subject: Discussion on device's runtime wake capability
Importance: High

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW, those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

But I may miss something, so it would be very kind of you to point it out if things are not like what I've thought, thanks.

BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

-Aaron

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Quoted 17 lines

-----Original Message-----
From: [email protected] [mailto:linux-acpi- [email protected]] On Behalf Of Aaron Lu
Sent: Tuesday, October 09, 2012 2:23 PM
To: Rafael J. Wysocki; Len Brown
Cc: Huang, Ying; Zhang, Rui; [email protected]
Subject: Discussion on device's runtime wake capability
Importance: High

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

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Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW, those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

Sounds reasonable to me.
To do runtime wake, we only need to power on the resources in _PR0.

Quoted 7 lines

But I may miss something, so it would be very kind of you to point it out if things are not like what I've thought, thanks.

BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

Agreed.

Quoted 6 lines

-Aaron

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To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html

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More majordomo info at http://vger.kernel.org/majordomo-info.html

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW,

those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

But I may miss something, so it would be very kind of you to point it out if things are not like what I've thought, thanks.

BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

Quoted 16 lines

-----Original Message-----
From: [email protected] [mailto:linux-acpi- [email protected]] On Behalf Of Aaron Lu
Sent: Tuesday, October 09, 2012 2:23 PM
To: Rafael J. Wysocki; Len Brown
Cc: Huang, Ying; Zhang, Rui; [email protected]
Subject: Discussion on device's runtime wake capability
Importance: High

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Quoted 6 lines

Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW, those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

Sounds reasonable to me.
To do runtime wake, we only need to power on the resources in _PR0.

Quoted 23 lines · Rui

Quoted 23 lines

-----Original Message-----
From: [email protected] [mailto:linux-acpi- [email protected]] On Behalf Of Aaron Lu
Sent: Tuesday, October 09, 2012 2:23 PM
To: Rafael J. Wysocki; Len Brown
Cc: Huang, Ying; Zhang, Rui; [email protected]
Subject: Discussion on device's runtime wake capability
Importance: High

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW, those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

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Sounds reasonable to me.
To do runtime wake, we only need to power on the resources in _PR0.

That would keep the device in D0 state :-)
We can put the device into a lower power state which _S0W permits for run wake.

Why do you think so? How can you be sure that those resources are not needed to provide wakeup power to the device (or whatever generates the wakeup signal on its behalf))?

Quoted 5 lines · On Tuesday 09 of October 2012 14:23:12 Aaron Lu wrote:

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Why not?

Quoted 3 lines

Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW,

Why do you think so? How can you be sure that those resources are not needed to provide wakeup power to the device (or whatever generates the wakeup signal on its behalf))?

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those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

Where did you get this idea from?

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But I may miss something, so it would be very kind of you to point it out if things are not like what I've thought, thanks.

Yes, you do. For example, _PRW gives us the number of the GPE to use for signalling wakeup, right?

Quoted 3 lines

BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

Yes, it is a _hint_.

Quoted 3 lines · Rafael J. Wysocki

Why do you think so? How can you be sure that those resources are not needed to provide wakeup power to the device (or whatever generates the wakeup signal on its behalf))?

Right. For instance, on some Thinkpads turning off the power resources cuts power to the port entirely - there's no way to generate wakeups if there's no 5V line...

Quoted 5 lines · Rafael J. Wysocki

Quoted 2 lines · On Tuesday 09 of October 2012 14:23:12 Aaron Lu wrote:

BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

Yes, it is a _hint_.

And I think it is a better hint than _PRW.

Quoted 7 lines · Rafael J. Wysocki

Quoted 5 lines · On Tuesday 09 of October 2012 14:23:12 Aaron Lu wrote:

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Quoted 1 line

Why not?

Section 7.2.13 of ACPI spec has words like this:
_PRW is only required for devices that have the ability to wake the system from a system sleeping state.

This is why I don't think _PRW is necessary for run wake as we are still at S0.

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Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW,

Why do you think so? How can you be sure that those resources are not needed to provide wakeup power to the device (or whatever generates the wakeup signal on its behalf))?

The same reason as above, the power resources are needed to arm the device to wake the system from a sleeping state, not S0.

But it's really good to know if there are systems that has a requirement for _PRW to be on for the device to wake itself up when system is at S0.

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those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

Where did you get this idea from?

Section 7.2.13 of ACPI spec.

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But I may miss something, so it would be very kind of you to point it out if things are not like what I've thought, thanks.

Yes, you do. For example, _PRW gives us the number of the GPE to use for signalling wakeup, right?

Yes, but I think this is a separate story.
The GPE will still be needed, but the power resources may not.

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BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

Yes, it is a _hint_.

And I think it is a better hint than _PRW.
I've seen a ACPI table that uses something like this to express the run wake of the device:
- It has _S0W;
- It has _DSW;
- No _PRW;
- It has a _CRS method to describe an interrupt resource.

And I've tested with a device which is able to both run wake and system wake. If I do not power those _PRW power resources, there is no problem for it to generate wake signal when system is at S0, and it even takes care of the GPE thing in ASL code. But this may be special cases, so I want to have a discussion on this.

So I hope we can refresh the way we check if the device is able to run wake.

And if possible, we can change the way we do to arm the device for run wake by not powering those _PRW power resources.

Quoted 14 lines · On Wednesday 10 of October 2012 08:53:32 Aaron Lu wrote:

Quoted 8 lines · Rafael J. Wysocki

Quoted 5 lines · On Tuesday 09 of October 2012 14:23:12 Aaron Lu wrote:

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Why not?

Section 7.2.13 of ACPI spec has words like this:
_PRW is only required for devices that have the ability to wake the system from a system sleeping state.

Quoted 2 lines

This is why I don't think _PRW is necessary for run wake as we are still at S0.

It may not be necessary, but if it is present, it gives us certain information about the device's wakeup capabilities.

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Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW,

Why do you think so? How can you be sure that those resources are not needed to provide wakeup power to the device (or whatever generates the wakeup signal on its behalf))?

Quoted 2 lines

The same reason as above, the power resources are needed to arm the device to wake the system from a sleeping state, not S0.

The spec doesn't say pretty much anything about S0 in that context and we found out some things by experimentation.

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But it's really good to know if there are systems that has a requirement for _PRW to be on for the device to wake itself up when system is at S0.

Yes, there are. Please see the Matthew's response.

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those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

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Where did you get this idea from?

Section 7.2.13 of ACPI spec.

I thought so. :-)

That part of the spec doesn't cover runtime wakeup at all, so I'm not sure it's a good reference.

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But I may miss something, so it would be very kind of you to point it out if things are not like what I've thought, thanks.

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Yes, you do. For example, _PRW gives us the number of the GPE to use for signalling wakeup, right?

Yes, but I think this is a separate story.
The GPE will still be needed, but the power resources may not.

They may or may not be needed, that's the problem. We basically cannot tell that just by reading the ACPI tables in many cases.

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BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

Yes, it is a _hint_.

Quoted 7 lines

And I think it is a better hint than _PRW.
I've seen a ACPI table that uses something like this to express the run wake of the device:
- It has _S0W;
- It has _DSW;
- No _PRW;
- It has a _CRS method to describe an interrupt resource.

That's fine I suppose, because this seems to be a device whose interrupt wakes it up. We didn't consider such devices before.

However, that doesn't mean that if _PRW _is_ defined and it lists some power resources, then those resources are only necessary for waking up the whole system from sleep states. They may be necessary for remote wakeup to work in S0 too.

Quoted 6 lines

And I've tested with a device which is able to both run wake and system wake. If I do not power those _PRW power resources, there is no problem for it to generate wake signal when system is at S0, and it even takes care of the GPE thing in ASL code. But this may be special cases, so I want to have a discussion on this.

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So I hope we can refresh the way we check if the device is able to run wake.

Yes, we can.

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And if possible, we can change the way we do to arm the device for run wake by not powering those _PRW power resources.

No, we can't.

Do you have examples of devices where it is harmful?

Quoted 15 lines · Rafael J. Wysocki

Quoted 14 lines · On Wednesday 10 of October 2012 08:53:32 Aaron Lu wrote:

Quoted 8 lines · Rafael J. Wysocki

Quoted 5 lines · On Tuesday 09 of October 2012 14:23:12 Aaron Lu wrote:

Hi all,

We are using _PRW as a hint to see if a device supports wakeup, this is fine for device which is able to wake the system in a sleep state, but not to wake itself when system is at S0.

Why not?

Section 7.2.13 of ACPI spec has words like this:
_PRW is only required for devices that have the ability to wake the system from a system sleeping state.

Quoted 5 lines

Quoted 2 lines

This is why I don't think _PRW is necessary for run wake as we are still at S0.

It may not be necessary, but if it is present, it gives us certain information about the device's wakeup capabilities.

Agree.

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Moreover, when we are to arm the device runtime wake, I think there is no need to power on the power resources referenced in _PRW,

Why do you think so? How can you be sure that those resources are not needed to provide wakeup power to the device (or whatever generates the wakeup signal on its behalf))?

Quoted 5 lines

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The same reason as above, the power resources are needed to arm the device to wake the system from a sleeping state, not S0.

The spec doesn't say pretty much anything about S0 in that context and we found out some things by experimentation.

OK.

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But it's really good to know if there are systems that has a requirement for _PRW to be on for the device to wake itself up when system is at S0.

Yes, there are. Please see the Matthew's response.

I was thinking in his example, the device may not have a _S0W object. I was waiting for his reply.

I agree that for devices only have _PRW but not _S0W, if we want run wake, we will need to power on _PRW.

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those power resources should be used to give the device ability to wake the system from a sleep state, not to wake itself when system is at S0, so powering thoses power resources on for run wake is a waste.

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Where did you get this idea from?

Section 7.2.13 of ACPI spec.

I thought so. :-)

That part of the spec doesn't cover runtime wakeup at all, so I'm not sure it's a good reference.

OK.

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But I may miss something, so it would be very kind of you to point it out if things are not like what I've thought, thanks.

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Yes, you do. For example, _PRW gives us the number of the GPE to use for signalling wakeup, right?

Yes, but I think this is a separate story.
The GPE will still be needed, but the power resources may not.

They may or may not be needed, that's the problem. We basically cannot tell that just by reading the ACPI tables in many cases.

It doesn't hurt if we enable the GPE, since either we as OSPM will enable it, or the ASL code will do that.

This is not like the power resources, which will waste some energy.

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BTW, _S0W seems to be a good hint whether the device supports run wake from ACPI's perspective.

Yes, it is a _hint_.

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And I think it is a better hint than _PRW.
I've seen a ACPI table that uses something like this to express the run wake of the device:
- It has _S0W;
- It has _DSW;
- No _PRW;
- It has a _CRS method to describe an interrupt resource.

That's fine I suppose, because this seems to be a device whose interrupt wakes it up. We didn't consider such devices before.

However, that doesn't mean that if _PRW _is_ defined and it lists some power resources, then those resources are only necessary for waking up the whole system from sleep states. They may be necessary for remote wakeup to work in S0 too.

Quoted 6 lines

And I've tested with a device which is able to both run wake and system wake. If I do not power those _PRW power resources, there is no problem for it to generate wake signal when system is at S0, and it even takes care of the GPE thing in ASL code. But this may be special cases, so I want to have a discussion on this.

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So I hope we can refresh the way we check if the device is able to run wake.

Yes, we can.

Good :-)

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And if possible, we can change the way we do to arm the device for run wake by not powering those _PRW power resources.

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No, we can't.

Do you have examples of devices where it is harmful?

Yes, for the ZPODD device.
It has _PRW specifying it can wake the system up from S4. And I tried not to powering on the power resources referenced in _PRW, no problem for it to generate wake event in S0.

Let me try to conclude:
- The behaviour of devices which only have _PRW should not be changed;
- We can change the way we check if a device is run wake capable by checking if it has _PRW or _S0W;
- For devices which have both _PRW and _S0W, we need consider if powering on _PRW is needed for run wake.

Does this look correct to you?

Quoted 8 lines · On Thursday 11 of October 2012 08:47:43 Aaron Lu wrote:

Quoted 7 lines · Rafael J. Wysocki

Quoted 2 lines · On Wednesday 10 of October 2012 08:53:32 Aaron Lu wrote:

And if possible, we can change the way we do to arm the device for run wake by not powering those _PRW power resources.

No, we can't.

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Do you have examples of devices where it is harmful?

Yes, for the ZPODD device.
It has _PRW specifying it can wake the system up from S4. And I tried not to powering on the power resources referenced in _PRW, no problem for it to generate wake event in S0.

How does it do that? Through the _PRW GPE or something else?

Quoted 7 lines

Let me try to conclude:
- The behaviour of devices which only have _PRW should not be changed;
- We can change the way we check if a device is run wake capable by checking if it has _PRW or _S0W;
- For devices which have both _PRW and _S0W, we need consider if powering on _PRW is needed for run wake.

Well, _S0W only tells us what power state(s) it is safe to put the device into without breaking its wakeup capability, but it doesn't really guarantee that, for example, the _PRW GPE will always work if the device is in one of the "safe" states.

My interpretation of the _PRW output is that it tells us the wakeup GPE number and a list of resources needed for that GPE to actually work. In which case it shouldn't matter whether or not the system is in S0.

From this, it sounds like if GPE is used, _PRW should always be turned on.

Quoted 9 lines · Rafael J. Wysocki

Quoted 8 lines · On Thursday 11 of October 2012 08:47:43 Aaron Lu wrote:

Quoted 7 lines · Rafael J. Wysocki

Quoted 2 lines · On Wednesday 10 of October 2012 08:53:32 Aaron Lu wrote:

And if possible, we can change the way we do to arm the device for run wake by not powering those _PRW power resources.

No, we can't.

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Do you have examples of devices where it is harmful?

Yes, for the ZPODD device.
It has _PRW specifying it can wake the system up from S4. And I tried not to powering on the power resources referenced in _PRW, no problem for it to generate wake event in S0.

How does it do that? Through the _PRW GPE or something else?

Yes, through the GPE defined in _PRW.

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Let me try to conclude:
- The behaviour of devices which only have _PRW should not be changed;
- We can change the way we check if a device is run wake capable by checking if it has _PRW or _S0W;
- For devices which have both _PRW and _S0W, we need consider if powering on _PRW is needed for run wake.

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Well, _S0W only tells us what power state(s) it is safe to put the device into without breaking its wakeup capability, but it doesn't really guarantee that, for example, the _PRW GPE will always work if the device is in one of the "safe" states.

Suppose _S0W returns 4, and its wake up event is sent through GPE defined in _PRW, and system is at S0. Do we need to turn on the power resources referenced in _PRW when we put the device into D3_COLD and its run wake capability is desired?

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My interpretation of the _PRW output is that it tells us the wakeup GPE number and a list of resources needed for that GPE to actually work. In which case it shouldn't matter whether or not the system is in S0.

From this, it sounds like if GPE is used, _PRW should always be turned on.