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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

  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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