From: Lukas Wunner <lukas@wunner.de>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Linux PM list <linux-pm@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Stern <stern@rowland.harvard.edu>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Tomeu Vizoso <tomeu.vizoso@collabora.com>,
Mark Brown <broonie@kernel.org>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Kevin Hilman <khilman@kernel.org>,
Ulf Hansson <ulf.hansson@linaro.org>,
"Luis R. Rodriguez" <mcgrof@suse.com>
Subject: Re: [RFC/RFT][PATCH v2 0/7] Functional dependencies between devices
Date: Sun, 18 Sep 2016 14:39:18 +0200 [thread overview]
Message-ID: <20160918123918.GB2169@wunner.de> (raw)
In-Reply-To: <4860126.rVrMyhOcY1@vostro.rjw.lan>
On Wed, Sep 14, 2016 at 01:18:16AM +0200, Rafael J. Wysocki wrote:
> On Tuesday, September 13, 2016 07:57:31 PM Lukas Wunner wrote:
> > To name a different use case: On hybrid graphics laptops, the discrete
> > GPU usually includes an HDA controller for external HDMI displays.
> > The GPU and the HDA controllers are siblings (functions 0 and 1 of a
> > PCI slot), yet in many laptops power is cut to both devices when _PS3
> > is executed for the GPU function. Currently we have a kludge where
> > the HDA controller is suspended before the GPU is powered down
> > (see vga_switcheroo_init_domain_pm_optimus_hdmi_audio()).
> >
> > I envision the HDA controller to be a consumer of the GPU in those
> > cases, thus ensuring that it's suspended before power is cut.
>
> So this example isn't a good one IMO. That clearly is a case when two
> (or more) devices share power resources controlled by a single on/off
> switch. Which is a clear use case for a PM domain.
TBH, I've never understood how a PM domain is supposed to solve this.
When power is cut at runtime for a struct dev_pm_domain, all devices
that were assigned this PM domain with dev_pm_domain_set() need to be
runtime suspended. This requires that a list of devices is maintained
which were assigned the same PM domain, and that the PM domain's
->runtime_suspend hook isn't executed before all of these devices have
runtime_suspended. Maybe I'm missing something but I don't see any code
to guarantee that in drivers/base/power/. Rather, the PM domain's
->runtime_suspend hook is executed as soon as one of the devices in the
PM domain runtime suspends, *without* taking into consideration the
other devices in the PM domain. They'll just be hanging in the air
with their device powered down.
>From what I've seen, people simply use struct dev_pm_domain as a way to
override the bus callbacks. At least that's what Dave Airlie does in
vga_switcheroo. But fundamentally that has nothing to do with shared
power resources, it only has to do with enforcing a different behaviour
than the bus.
Thus I don't understand what you mean if you say this is a use case for
a PM domain.
> > I'm sure there are situations where a driver presence dependency
> > is needed between parent/child and you should fully expect that
> > developers will try to employ device links for these use cases.
> > Which means that the code for suspend/resume device ordering is
> > executed twice.
>
> Creating a link between a parent and child would be a bug. I guess
> device_link_add() should just return NULL on an attempt to do that.
To be clear, while linking a parent (as consumer) to a child
(as supplier) needs to be prevented since it introduces a dependency
loop, the converse should IMO be allowed.
That would be the case when someone needs a driver presence dependency,
but doesn't need a suspend/resume ordering dependency (because it's
already guaranteed by the PM core for parent/child). In that case the
child will simultaneously be a consumer, which means e.g. that dpm_wait()
will be executed twice for the same device, but that overhead is probably
negligible.
Thanks,
Lukas
next prev parent reply other threads:[~2016-09-18 12:38 UTC|newest]
Thread overview: 138+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-08 21:25 [RFC/RFT][PATCH v2 0/7] Functional dependencies between devices Rafael J. Wysocki
2016-09-08 21:26 ` [RFC/RFT][PATCH v2 1/7] driver core: Add a wrapper around __device_release_driver() Rafael J. Wysocki
2016-09-08 21:27 ` [RFC/RFT][PATCH v2 2/7] driver core: Functional dependencies tracking support Rafael J. Wysocki
2016-09-09 8:25 ` Ulf Hansson
2016-09-09 12:06 ` Mark Brown
2016-09-09 14:13 ` Ulf Hansson
2016-09-15 1:11 ` Rafael J. Wysocki
2016-09-11 13:40 ` Lukas Wunner
2016-09-11 20:43 ` Lukas Wunner
2016-09-14 1:21 ` Rafael J. Wysocki
2016-09-14 8:28 ` Lukas Wunner
2016-09-14 13:17 ` Rafael J. Wysocki
2016-09-08 21:28 ` [RFC/RFT][PATCH v2 3/7] PM / sleep: Make async suspend/resume of devices use device links Rafael J. Wysocki
2016-09-10 13:31 ` Lukas Wunner
2016-09-10 22:12 ` Rafael J. Wysocki
2016-09-08 21:29 ` [RFC/RFT][PATCH v2 4/7] PM / runtime: Pass flags argument to __pm_runtime_disable() Rafael J. Wysocki
2016-09-08 21:29 ` [RFC/RFT][PATCH v2 5/7] PM / runtime: Flag to indicate PM sleep transitions in progress Rafael J. Wysocki
2016-09-12 14:07 ` Lukas Wunner
2016-09-12 21:25 ` Rafael J. Wysocki
2016-09-12 22:52 ` Lukas Wunner
2016-09-13 7:21 ` Marek Szyprowski
2016-09-13 23:59 ` Rafael J. Wysocki
2016-09-08 21:30 ` [RFC/RFT][PATCH v2 6/7] PM / runtime: Use device links Rafael J. Wysocki
2016-09-12 9:47 ` Lukas Wunner
2016-09-12 13:57 ` Rafael J. Wysocki
2016-09-14 1:19 ` Rafael J. Wysocki
2016-09-08 21:31 ` [RFC/RFT][PATCH v2 7/7] PM / runtime: Optimize the use of " Rafael J. Wysocki
2016-09-08 21:35 ` [RFC/RFT][PATCH v2 0/7] Functional dependencies between devices Rafael J. Wysocki
2016-09-10 11:39 ` Lukas Wunner
2016-09-10 22:04 ` Rafael J. Wysocki
2016-09-13 17:57 ` Lukas Wunner
2016-09-13 23:18 ` Rafael J. Wysocki
2016-09-18 12:39 ` Lukas Wunner [this message]
[not found] ` <CGME20160913095858eucas1p267ec2397c9e4577f94557e4a38498164@eucas1p2.samsung.com>
2016-09-13 9:58 ` Marek Szyprowski
2016-09-13 22:41 ` Rafael J. Wysocki
2016-09-18 11:23 ` Lukas Wunner
2016-09-15 22:03 ` [RFC/RFT][PATCH v3 0/5] " Rafael J. Wysocki
2016-09-15 22:04 ` [Resend][RFC/RFT][PATCH v3 1/5] driver core: Add a wrapper around __device_release_driver() Rafael J. Wysocki
2016-09-15 22:06 ` [RFC/RFT][PATCH v3 2/5] driver core: Functional dependencies tracking support Rafael J. Wysocki
2016-09-16 7:53 ` Marek Szyprowski
2016-09-16 12:06 ` Rafael J. Wysocki
2016-09-16 12:33 ` [Update][RFC/RFT][PATCH " Rafael J. Wysocki
2016-09-19 22:46 ` Lukas Wunner
2016-09-23 13:03 ` Lukas Wunner
2016-09-23 13:42 ` Rafael J. Wysocki
2016-09-26 16:51 ` Lukas Wunner
2016-09-27 12:16 ` Rafael J. Wysocki
2016-09-27 8:54 ` Lukas Wunner
2016-09-27 11:52 ` Rafael J. Wysocki
2016-09-28 10:43 ` Lukas Wunner
2016-09-28 11:31 ` Rafael J. Wysocki
2016-09-29 10:36 ` Lukas Wunner
2016-09-15 22:06 ` [RFC/RFT][PATCH v3 3/5] PM / sleep: Make async suspend/resume of devices use device links Rafael J. Wysocki
2016-09-15 22:07 ` [RFC/RFT][PATCH v3 4/5] PM / runtime: Use " Rafael J. Wysocki
2016-09-15 22:07 ` [RFC/RFT][PATCH v3 5/5] PM / runtime: Optimize the use of " Rafael J. Wysocki
2016-09-16 7:25 ` [RFC/RFT][PATCH v3 0/5] Functional dependencies between devices Marek Szyprowski
2016-09-16 7:57 ` Marek Szyprowski
2016-09-16 12:04 ` Rafael J. Wysocki
2016-09-27 12:34 ` Lukas Wunner
2016-09-28 0:33 ` Rafael J. Wysocki
2016-09-28 11:42 ` Lukas Wunner
2016-09-29 0:51 ` Rafael J. Wysocki
2016-11-15 18:50 ` Lukas Wunner
2016-09-29 0:24 ` [PATCH v4 " Rafael J. Wysocki
2016-09-29 0:25 ` [Resend][PATCH v4 1/5] driver core: Add a wrapper around __device_release_driver() Rafael J. Wysocki
2016-09-29 0:38 ` [PATCH v4 2/5] driver core: Functional dependencies tracking support Rafael J. Wysocki
2016-10-01 7:43 ` Lukas Wunner
2016-10-01 23:32 ` Rafael J. Wysocki
2016-09-29 0:38 ` [Resend][PATCH v4 3/5] PM / sleep: Make async suspend/resume of devices use device links Rafael J. Wysocki
2016-09-29 0:40 ` [PATCH v4 4/5] PM / runtime: Use " Rafael J. Wysocki
2016-09-29 0:41 ` [Rebase][PATCH v4 5/5] PM / runtime: Optimize the use of " Rafael J. Wysocki
2016-09-29 6:58 ` [PATCH v4 0/5] Functional dependencies between devices Marek Szyprowski
2016-09-29 12:27 ` Rafael J. Wysocki
2016-10-02 23:13 ` Lukas Wunner
2016-10-10 12:36 ` [PATCH v5 " Rafael J. Wysocki
2016-10-10 12:37 ` [Resend][PATCH v5 1/5] driver core: Add a wrapper around __device_release_driver() Rafael J. Wysocki
2016-10-10 12:51 ` [PATCH v5 2/5] driver core: Functional dependencies tracking support Rafael J. Wysocki
2016-10-26 11:19 ` Lukas Wunner
2016-10-27 15:25 ` Greg Kroah-Hartman
2016-10-28 9:57 ` Lukas Wunner
2016-11-07 21:22 ` Luis R. Rodriguez
2016-11-08 6:45 ` Greg Kroah-Hartman
2016-11-08 19:21 ` Luis R. Rodriguez
2016-11-08 19:43 ` Greg Kroah-Hartman
2016-11-08 20:58 ` Luis R. Rodriguez
2016-11-09 6:45 ` Greg Kroah-Hartman
2016-11-09 9:36 ` Andrzej Hajda
2016-11-09 9:41 ` Greg Kroah-Hartman
2016-11-13 16:58 ` Lukas Wunner
2016-11-10 0:43 ` Rafael J. Wysocki
2016-11-10 0:59 ` Luis R. Rodriguez
2016-11-10 7:14 ` Laurent Pinchart
2016-11-10 22:04 ` Luis R. Rodriguez
2016-11-10 22:40 ` Greg Kroah-Hartman
2016-11-11 0:08 ` Laurent Pinchart
2016-11-13 10:59 ` Greg Kroah-Hartman
2016-11-14 14:50 ` Luis R. Rodriguez
2016-11-14 8:15 ` Geert Uytterhoeven
2016-11-10 8:46 ` Geert Uytterhoeven
2016-11-10 22:12 ` Luis R. Rodriguez
2016-10-27 15:32 ` Greg Kroah-Hartman
2016-11-07 21:39 ` Luis R. Rodriguez
2016-11-10 1:07 ` Rafael J. Wysocki
2016-11-10 7:05 ` Laurent Pinchart
2016-11-10 23:09 ` Luis R. Rodriguez
2016-11-13 17:34 ` Lukas Wunner
2016-11-14 13:48 ` Luis R. Rodriguez
2016-11-14 15:48 ` Lukas Wunner
2016-11-14 16:00 ` Luis R. Rodriguez
2016-10-10 12:54 ` [PATCH v5 3/5] PM / sleep: Make async suspend/resume of devices use device links Rafael J. Wysocki
2016-10-10 12:56 ` [PATCH v5 4/5] PM / runtime: Use " Rafael J. Wysocki
2016-10-20 13:17 ` [Update][PATCH " Rafael J. Wysocki
2016-10-10 12:57 ` [Rebase][PATCH v5 5/5] PM / runtime: Optimize the use of " Rafael J. Wysocki
2016-10-18 10:46 ` [PATCH v5 0/5] Functional dependencies between devices Marek Szyprowski
2016-10-19 11:57 ` Rafael J. Wysocki
2016-10-20 10:21 ` Marek Szyprowski
2016-10-20 12:54 ` Rafael J. Wysocki
2016-10-27 15:32 ` Greg Kroah-Hartman
[not found] ` <5811F0CF.5000204@huawei.com>
2016-10-28 9:39 ` Lukas Wunner
2016-11-02 20:55 ` Hanjun Guo
2016-10-30 16:22 ` [PATCH v6 " Rafael J. Wysocki
2016-10-30 16:28 ` [Resend][PATCH v6 3/5] PM / sleep: Make async suspend/resume of devices use device links Rafael J. Wysocki
2016-10-30 16:29 ` [Resend][PATCH v6 1/5] driver core: Add a wrapper around __device_release_driver() Rafael J. Wysocki
2016-10-30 16:32 ` [PATCH v6 2/5] driver core: Functional dependencies tracking support Rafael J. Wysocki
2016-10-30 16:32 ` [PATCH v6 4/5] PM / runtime: Use device links Rafael J. Wysocki
2016-12-18 14:01 ` Lukas Wunner
2016-12-18 15:53 ` Rafael J. Wysocki
2016-12-18 16:37 ` Lukas Wunner
2016-12-19 12:38 ` Rafael J. Wysocki
2016-10-30 16:32 ` [Resend][PATCH v6 5/5] PM / runtime: Optimize the use of " Rafael J. Wysocki
2016-10-30 16:40 ` [PATCH v6 0/5] Functional dependencies between devices Rafael J. Wysocki
2016-10-31 17:47 ` Greg Kroah-Hartman
2016-11-01 3:50 ` Rafael J. Wysocki
2016-11-02 7:58 ` Marek Szyprowski
2016-11-05 12:10 ` Greg Kroah-Hartman
2016-11-07 21:15 ` Luis R. Rodriguez
2016-11-08 6:36 ` Marek Szyprowski
2016-11-08 20:14 ` Luis R. Rodriguez
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