subject:"CPUIdle for Exynos5422 Odroid\-XU3\/XU4 boards."

Re: CPUIdle for Exynos5422 Odroid-XU3/XU4 boards.

2015-10-12 Thread Amit Kucheria

On Fri, Aug 28, 2015 at 6:12 PM, Krzysztof Kozlowski
 wrote:
> W dniu 28.08.2015 o 17:35, Javier Martinez Canillas pisze:

>>
>> Ok, I'll see if I can take a look what is needed to implement a Exynos542x 
>> CPUidle
>> driver. I'm quite busy with other stuff right now but I should be less busy 
>> in a
>> couple of weeks.
>
> The only useful users of Exynos542x cpuidle would be Chromebooks.
> Probably the same goes with suspend to RAM. Non-mobile devices could
> leave without it.
>
> In the same time cpuidle and S2R would require a significant amount of
> work. Testing would have to be performed on Chromebooks. I have doubts
> it would work on Odroid XU3.
>
> I dug into S2R issues on Odroid XU3 and after fixing trivial imprecise
> abort I don't have clue. It just dies somewhere in firmware/bootloader.
> Vendor code has a lot more stuff related to suspend and testing it
> one-by-one whether it fixes the issue is frustrating.
>
> Do we really need cpuidle or S2R on Exynos542x/5800?

Cpuidle support on Odroid-XU3 and Peach-Pi would be useful for general
PM/scheduler work on big.LITTLE systems. On the Odroid, it has the
additional benefit of allowing power measurements, which helps.

Regards,
Amit
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Re: CPUIdle for Exynos5422 Odroid-XU3/XU4 boards.

2015-08-28 Thread Javier Martinez Canillas

Hello Bartlomiej and Lorenzo,

Thanks a lot for your explanations.

On 08/27/2015 06:58 PM, Bartlomiej Zolnierkiewicz wrote:

Hi,

On Tuesday, August 25, 2015 05:09:32 PM Lorenzo Pieralisi wrote:
On Tue, Aug 25, 2015 at 03:35:29PM +0100, Bartlomiej Zolnierkiewicz wrote:

[ added Lorenzo and linux-pm to Cc: ]

Hi,

On Tuesday, August 25, 2015 11:43:38 AM Javier Martinez Canillas wrote:
[adding Kevin Hilman as cc who was also interested in CPUidle for Exynos]

Hello Krzysztof,

On 08/23/2015 03:26 AM, Krzysztof Kozlowski wrote:

[snip]

2015-08-21 16:21 GMT+09:00 Javier Martinez Canillas
jav...@osg.samsung.com:

The big.LITTLE cpuidle driver is not a typical Exynos cpuidle driver.
It only executes CPU suspend on a cluster which essentially is a power
down operation.

You are correct, looking at the the big.LITTLE CPUidle driver I see that
it only has two C-states: C0 (normal WFI) and C1 (single CPU power-down)
which as you said, places the CPU into power-down mode by using the MCPM
infrastructure so it's basically a CPU suspend AFAIU.

So what you are saying is that there are deeper C-states supported by the
Exynos 542x SoC family but these are not handled by the b.L CPUidle driver.

When we talk about cpuidle on Exynos, we have in mind one of sleep
modes: AFTR or LPA (sometimes instead of LPA there is LPD or W-AFTR).
Actually this is more like a system idle mode, not CPU idle. The power
savings are much bigger than disabling only one cluster.

Interesting, I was not aware of AFTR and LPA but I looked in the manual
now.
Thanks a lot for the information.

I see that the Exynos CPUidle driver (drivers/cpuidle/cpuidle-exynos.c)
also
has only two C-states (WFI and C1) but C1 makes the system to enter in AFTR
(system-level power gating).

This is similar to what the downstream ChromiumOS 3.8 kernel CPUidle driver
does IIUC [0].

Yes but upstream does it in a clean way, has support for platforms
requiring secure firmware operations and also implements coupled
AFTR mode on a few platforms.

So the question is still valid - whether someone wants or plans to
implement cpuidle for Exynos 542x family. Odroid XU3 is not a priority
here because energy consumption is not an issue there. This is not a
mobile device.

That's true but it will be interesting for the 5420 and 5800 based
Chromebooks since optimizing power consumption would be useful there.

I would be happy to help with reviewing patches etc. but personally
I don't have any plans for doing this work. I may look into adding
support for newer ARM64 SoCs (Exynos5433) if I find some extra time
(quite unlikely currently).

I thought that big.LITTLE platforms were encouraged to use the generic b.L
CPUidle driver just like DT platforms should use the generic CPUFreq DT
driver but I guess I misunderstood.

So the b.L CPUidle driver is only to have minimum CPUidle support but a SoC
specific driver is needed to fine tune and get most out of the platform?

Or should the b.L CPUidle driver be extended to add per platform C-states?

This is a good question. Daniel/Lorenzo?

To move the b.L driver to multiple C-states we should first convert it to
the generic CPUidle driver (by defining an MCPM enable-method):

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/cpuidle/cpuidle-arm.c?id=refs/tags/v4.2-rc8

Then we have to figure out how to determine how many CPUidle drivers we
have to create (since idle states are different on different CPUs), since
using the MIDR does not really scale.

For certain I won't support coupled C-states in the DT idle states code,
and every platform requiring them is considered buggy and not worth
merging in the mainline kernel from now onwards, HW should be fixed,
eventually, I am not willing to see code like
drivers/cpuidle/cpuidle-exynos.c in the mainline kernel anymore,
I am sorry.

For Exynos chipsets coupled C-states are not strictly required for
having cpuidle support but make it more useful. On Exynos chipsets
secondary CPUs must be disabled to allow system to go into deeper
idle modes and this is assured by using coupled C-states. Original
Android drivers don't use coupled C-states and depend on the rest
of the system to offline secondary CPUs when not needed.

I would of course prefer not to have handle this in software and
be automatically handled by hardware/firmware but that doesn't mean
that we should be declining mainline support for ugly hardware
(this has never been the Linux way of doing things).

Coming back to the platforms in question (ARM32 big.LITTLE based
Odroid XU3 boards etc.) they have been shipped long time ago and
the best we can do nowadays is to support them as well as possible.

I agree.

If somebody wants to implement a separate Exynos542x/Exynos5800
big.LITTLE cpuidle driver for them I see no problem with it and I'm
willing to help in maintaining it.

Ok, I'll see if I can take a look what

Re: CPUIdle for Exynos5422 Odroid-XU3/XU4 boards.

2015-08-28 Thread Krzysztof Kozlowski

W dniu 28.08.2015 o 17:35, Javier Martinez Canillas pisze:
 Hello Bartlomiej and Lorenzo,
 
 Thanks a lot for your explanations.
 
 On 08/27/2015 06:58 PM, Bartlomiej Zolnierkiewicz wrote:

 If somebody wants to implement a separate Exynos542x/Exynos5800
 big.LITTLE cpuidle driver for them I see no problem with it and I'm
 willing to help in maintaining it.

 
 Ok, I'll see if I can take a look what is needed to implement a Exynos542x 
 CPUidle
 driver. I'm quite busy with other stuff right now but I should be less busy 
 in a
 couple of weeks.

The only useful users of Exynos542x cpuidle would be Chromebooks.
Probably the same goes with suspend to RAM. Non-mobile devices could
leave without it.

In the same time cpuidle and S2R would require a significant amount of
work. Testing would have to be performed on Chromebooks. I have doubts
it would work on Odroid XU3.

I dug into S2R issues on Odroid XU3 and after fixing trivial imprecise
abort I don't have clue. It just dies somewhere in firmware/bootloader.
Vendor code has a lot more stuff related to suspend and testing it
one-by-one whether it fixes the issue is frustrating.

Do we really need cpuidle or S2R on Exynos542x/5800?

 
 Maybe is a little bit out of topic but since Anand also asked about CPUFreq 
 support,
 are you planning on re-posting your cpufreq: add generic cpufreq driver 
 support
 for Exynos5250/5800 platforms [0] series?

That would be useful. Bartlomiej, do you have plans for continuing the work?

Best regards,
Krzysztof

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Re: CPUIdle for Exynos5422 Odroid-XU3/XU4 boards.

2015-08-28 Thread Bartlomiej Zolnierkiewicz


Hi,

On Friday, August 28, 2015 09:42:35 PM Krzysztof Kozlowski wrote:
 W dniu 28.08.2015 o 17:35, Javier Martinez Canillas pisze:
  Hello Bartlomiej and Lorenzo,
  
  Thanks a lot for your explanations.
  
  On 08/27/2015 06:58 PM, Bartlomiej Zolnierkiewicz wrote:
 
  If somebody wants to implement a separate Exynos542x/Exynos5800
  big.LITTLE cpuidle driver for them I see no problem with it and I'm
  willing to help in maintaining it.
 
  
  Ok, I'll see if I can take a look what is needed to implement a Exynos542x 
  CPUidle
  driver. I'm quite busy with other stuff right now but I should be less busy 
  in a
  couple of weeks.
 
 The only useful users of Exynos542x cpuidle would be Chromebooks.
 Probably the same goes with suspend to RAM. Non-mobile devices could
 leave without it.
 
 In the same time cpuidle and S2R would require a significant amount of
 work. Testing would have to be performed on Chromebooks. I have doubts
 it would work on Odroid XU3.
 
 I dug into S2R issues on Odroid XU3 and after fixing trivial imprecise
 abort I don't have clue. It just dies somewhere in firmware/bootloader.
 Vendor code has a lot more stuff related to suspend and testing it
 one-by-one whether it fixes the issue is frustrating.
 
 Do we really need cpuidle or S2R on Exynos542x/5800?
 
  
  Maybe is a little bit out of topic but since Anand also asked about CPUFreq 
  support,
  are you planning on re-posting your cpufreq: add generic cpufreq driver 
  support
  for Exynos5250/5800 platforms [0] series?
 
 That would be useful. Bartlomiej, do you have plans for continuing the work?

Yes.  It is still on my TODO but may take a while (1-2 weeks) before
I find some time to actually do it.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung RD Institute Poland
Samsung Electronics

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Re: CPUIdle for Exynos5422 Odroid-XU3/XU4 boards.

2015-08-27 Thread Bartlomiej Zolnierkiewicz

Hi,

On Tuesday, August 25, 2015 05:09:32 PM Lorenzo Pieralisi wrote:
On Tue, Aug 25, 2015 at 03:35:29PM +0100, Bartlomiej Zolnierkiewicz wrote:

[ added Lorenzo and linux-pm to Cc: ]

Hi,

On Tuesday, August 25, 2015 11:43:38 AM Javier Martinez Canillas wrote:
[adding Kevin Hilman as cc who was also interested in CPUidle for Exynos]

Hello Krzysztof,

On 08/23/2015 03:26 AM, Krzysztof Kozlowski wrote:

[snip]

2015-08-21 16:21 GMT+09:00 Javier Martinez Canillas
jav...@osg.samsung.com:

The big.LITTLE cpuidle driver is not a typical Exynos cpuidle driver.
It only executes CPU suspend on a cluster which essentially is a power
down operation.

So what you are saying is that there are deeper C-states supported by the
Exynos 542x SoC family but these are not handled by the b.L CPUidle
driver.

Interesting, I was not aware of AFTR and LPA but I looked in the manual
now.
Thanks a lot for the information.

I see that the Exynos CPUidle driver (drivers/cpuidle/cpuidle-exynos.c)
also
has only two C-states (WFI and C1) but C1 makes the system to enter in
AFTR
(system-level power gating).

This is similar to what the downstream ChromiumOS 3.8 kernel CPUidle
driver
does IIUC [0].

Yes but upstream does it in a clean way, has support for platforms
requiring secure firmware operations and also implements coupled
AFTR mode on a few platforms.

That's true but it will be interesting for the 5420 and 5800 based
Chromebooks since optimizing power consumption would be useful there.

I thought that big.LITTLE platforms were encouraged to use the generic b.L
CPUidle driver just like DT platforms should use the generic CPUFreq DT
driver but I guess I misunderstood.

So the b.L CPUidle driver is only to have minimum CPUidle support but a
SoC
specific driver is needed to fine tune and get most out of the platform?

Or should the b.L CPUidle driver be extended to add per platform C-states?

This is a good question. Daniel/Lorenzo?

To move the b.L driver to multiple C-states we should first convert it to
the generic CPUidle driver (by defining an MCPM enable-method):

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/cpuidle/cpuidle-arm.c?id=refs/tags/v4.2-rc8

Then we have to figure out how to determine how many CPUidle drivers we
have to create (since idle states are different on different CPUs), since
using the MIDR does not really scale.

Coming back to the platforms in question (ARM32 big.LITTLE based
Odroid XU3 boards etc.) they have been shipped long time ago and
the best we can do nowadays is to support them as well as possible.

If somebody wants to implement a separate Exynos542x/Exynos5800
big.LITTLE cpuidle driver for them I see no problem with it and I'm
willing to help in maintaining it.

Re: CPUIdle for Exynos5422 Odroid-XU3/XU4 boards.

2015-08-25 Thread Bartlomiej Zolnierkiewicz

[ added Lorenzo and linux-pm to Cc: ]

Hi,

On Tuesday, August 25, 2015 11:43:38 AM Javier Martinez Canillas wrote:
[adding Kevin Hilman as cc who was also interested in CPUidle for Exynos]

Hello Krzysztof,

On 08/23/2015 03:26 AM, Krzysztof Kozlowski wrote:

[snip]

2015-08-21 16:21 GMT+09:00 Javier Martinez Canillas
jav...@osg.samsung.com:

The big.LITTLE cpuidle driver is not a typical Exynos cpuidle driver.
It only executes CPU suspend on a cluster which essentially is a power
down operation.

So what you are saying is that there are deeper C-states supported by the
Exynos 542x SoC family but these are not handled by the b.L CPUidle driver.

Interesting, I was not aware of AFTR and LPA but I looked in the manual now.
Thanks a lot for the information.

I see that the Exynos CPUidle driver (drivers/cpuidle/cpuidle-exynos.c) also
has only two C-states (WFI and C1) but C1 makes the system to enter in AFTR
(system-level power gating).

This is similar to what the downstream ChromiumOS 3.8 kernel CPUidle driver
does IIUC [0].

Yes but upstream does it in a clean way, has support for platforms
requiring secure firmware operations and also implements coupled
AFTR mode on a few platforms.

That's true but it will be interesting for the 5420 and 5800 based
Chromebooks since optimizing power consumption would be useful there.

I thought that big.LITTLE platforms were encouraged to use the generic b.L
CPUidle driver just like DT platforms should use the generic CPUFreq DT
driver but I guess I misunderstood.

So the b.L CPUidle driver is only to have minimum CPUidle support but a SoC
specific driver is needed to fine tune and get most out of the platform?

Or should the b.L CPUidle driver be extended to add per platform C-states?

This is a good question. Daniel/Lorenzo?

Best regards,
Krzysztof

[0]:
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/chromeos-3.8/arch/arm/mach-exynos/cpuidle.c

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung RD Institute Poland
Samsung Electronics

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Re: CPUIdle for Exynos5422 Odroid-XU3/XU4 boards.

2015-08-25 Thread Lorenzo Pieralisi

On Tue, Aug 25, 2015 at 03:35:29PM +0100, Bartlomiej Zolnierkiewicz wrote: