linux-kernel - Re: [PATCH] PM / QoS: Fix default runtime

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Message-ID: <1785554.vpm9XMd3xA@avalon>
Date:   Tue, 31 Oct 2017 19:12:04 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Tero Kristo <t-kristo@...com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] PM / QoS: Fix default runtime_pm device resume latency

Hi Geert,

On Tuesday, 31 October 2017 15:55:02 EET Geert Uytterhoeven wrote:
> On Tue, Oct 31, 2017 at 2:10 PM, Geert Uytterhoeven wrote:
> > On Tue, Oct 31, 2017 at 2:09 PM, Geert Uytterhoeven wrote:
> >> On Tue, Oct 31, 2017 at 12:27 AM, Rafael J. Wysocki 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@...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@...com>
> >>>>> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.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.

Thank you for tracking this and notifying me. I like it even better now that 
the problem seems to be fixed without requiring any action from my side :-)

> >> Do you have a clue?
> >> Thanks!

-- 
Regards,

Laurent Pinchart