Re: [PATCH] PM / QoS: Fix default runtime_pm device resume latency

["Rafael J. Wysocki" <rafael@kernel.org>]

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On Tue, Oct 31, 2017 at 2:55 PM, Geert Uytterhoeven
<geert@linux-m68k.org> wrote:
> Hi Rafael, Tero,
>
> CC pinchartl, dri-devel
>
> On Tue, Oct 31, 2017 at 2:10 PM, Geert Uytterhoeven
> <geert@linux-m68k.org> wrote:
>> CC linux-renesas-soc
>>
>> On Tue, Oct 31, 2017 at 2:09 PM, Geert Uytterhoeven
>> <geert@linux-m68k.org> wrote:
>>> On Tue, Oct 31, 2017 at 12:27 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>>>> On Monday, October 30, 2017 11:19:08 AM CET Rafael J. Wysocki wrote:
>>>>> On Mon, Oct 30, 2017 at 8:10 AM, Tero Kristo <t-kristo@ti.com> wrote:
>>>>> > The recent change to the PM QoS framework to introduce a proper
>>>>> > no constraint value overlooked to handle the devices which don't
>>>>> > implement PM QoS OPS. Runtime PM is one of the more severely
>>>>> > impacted subsystems, failing every attempt to runtime suspend
>>>>> > a device. This leads into some nasty second level issues like
>>>>> > probe failures and increased power consumption among other things.
>>>>>
>>>>> Oh, that's bad.
>>>>>
>>>>> Sorry about breaking it and thanks for the fix!
>>>>>
>>>>> > Fix this by adding a proper return value for devices that don't
>>>>> > implement PM QoS implicitly.
>>>>> >
>>>>> > Fixes: 0cc2b4e5a020 ("PM / QoS: Fix device resume latency PM QoS")
>>>>> > Signed-off-by: Tero Kristo <t-kristo@ti.com>
>>>>> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>>>
>>>>> Applied.
>>>>
>>>> And pushed to Linus.
>>>
>>> I'm afraid it is not sufficient.
>>>
>>> Commit 0cc2b4e5a020fc7f ("PM / QoS: Fix device resume latency PM QoS")
>>> introduced two issues on Renesas platforms:
>>>  1. After boot up, many devices have changed their state from "suspended"
>>>     to "active", according to /sys/kernel/debug/pm_genpd/pm_genpd_summary
>>>     (comparing that file across boots is one of my standard tests).
>>>     Interestingly, doing a system suspend/resume cycle restores their state
>>>     to "suspended".
>>>
>>>  2. During system suspend, the following warning is printed on
>>>     r8a7791/koelsch:
>>>
>>>         i2c-rcar e6530000.i2c: runtime PM trying to suspend device but
>>> active child
>
>  3. I've just bisected a seemingly unrelated issue to the same commit.
>     On Salvator-XS with R-Car H3, initialization of the rcar-du driver now
>     takes more than 1 minute due to flip_done time outs, while it took 0.12s
>     before:
>
>     [    3.015035] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
>     [    3.021721] [drm] No driver support for vblank timestamp query.
>     [   13.280738] [drm:drm_atomic_helper_wait_for_flip_done] *ERROR*
> [CRTC:58:crtc-3] flip_done timed out
>     [   23.520707] [drm:drm_atomic_helper_commit_cleanup_done] *ERROR*
> [CRTC:58:crtc-3] flip_done timed out
>     [   33.760708] [drm:drm_atomic_helper_wait_for_flip_done] *ERROR*
> [CRTC:58:crtc-3] flip_done timed out
>     [   44.000755] [drm:drm_atomic_helper_commit_cleanup_done] *ERROR*
> [CRTC:58:crtc-3] flip_done timed out
>     [   44.003597] Console: switching to colour frame buffer device 128x48
>     [   54.240707] [drm:drm_atomic_helper_wait_for_flip_done] *ERROR*
> [CRTC:58:crtc-3] flip_done timed out
>     [   64.480706] [drm:drm_atomic_helper_commit_cleanup_done] *ERROR*
> [CRTC:58:crtc-3] flip_done timed out
>     [   64.544876] rcar-du feb00000.display: fb0:  frame buffer device
>     [   64.552013] [drm] Initialized rcar-du 1.0.0 20130110 for
> feb00000.display on minor 0
>     [   64.559873] [drm] Device feb00000.display probed
>
>>> Commit 2a9a86d5c81389cd ("PM / QoS: Fix default runtime_pm device resume
>>> latency") fixes the second issue, but not the first.
>
> ... nor the third.
>
>>> Reverting commits 2a9a86d5c81389cd ("PM / QoS: Fix default runtime_pm
>>> device resume latency") and 0cc2b4e5a020fc7f ("PM / QoS: Fix device resume
>>> latency PM QoS") fixes both.
>
> ... all three.

Sorry for the breakage.

OK, I'll just push the reverts to Linus later today.

>>> Do you have a clue?

Well, kind of.

There is a change in behavior in domain_governor.c that should not
have made any difference to my eyes, but maybe that's it.

Can you please check if the attached patch makes any difference?

Thanks,
Rafael

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---
 drivers/base/power/domain_governor.c |   11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/base/power/domain_governor.c
===================================================================
--- linux-pm.orig/drivers/base/power/domain_governor.c
+++ linux-pm/drivers/base/power/domain_governor.c
@@ -83,12 +83,11 @@ static bool default_suspend_ok(struct de
 		td->cached_suspend_ok = true;
 	} else {
 		constraint_ns -= td->suspend_latency_ns + td->resume_latency_ns;
-		if (constraint_ns > 0) {
-			td->effective_constraint_ns = constraint_ns;
-			td->cached_suspend_ok = true;
-		} else {
-			td->effective_constraint_ns = 0;
-		}
+		if (constraint_ns == 0)
+			return false;
+
+		td->effective_constraint_ns = constraint_ns;
+		td->cached_suspend_ok = constraint_ns >= 0;
 	}
 
 	/*