From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Ulf Hansson <ulf.hansson@linaro.org>
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>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Lukas Wunner <lukas@wunner.de>, Kevin Hilman <khilman@kernel.org>,
"Luis R. Rodriguez" <mcgrof@suse.com>,
Mark Brown <broonie@kernel.org>
Subject: Re: [RFC/RFT][PATCH v2 2/7] driver core: Functional dependencies tracking support
Date: Thu, 15 Sep 2016 03:11:55 +0200 [thread overview]
Message-ID: <1763647.dzavfRICAb@vostro.rjw.lan> (raw)
In-Reply-To: <CAPDyKFpTeB8MLXihpTnyk9RerVC_PNp8ogXG6aATLT2xLkp9mA@mail.gmail.com>
On Friday, September 09, 2016 10:25:30 AM Ulf Hansson wrote:
> + Mark
>
> On 8 September 2016 at 23:27, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Currently, there is a problem with handling cases where functional
> > dependencies between devices are involved.
> >
> > What I mean by a "functional dependency" is when the driver of device
> > B needs both device A and its driver to be present and functional to
> > be able to work. This implies that the driver of A needs to be
> > working for B to be probed successfully and it cannot be unbound from
> > the device before the B's driver. This also has certain consequences
> > for power management of these devices (suspend/resume and runtime PM
> > ordering).
> >
> > Add support for representing those functional dependencies between
> > devices to allow the driver core to track them and act on them in
> > certain cases where they matter.
> >
> > The argument for doing that in the driver core is that there are
> > quite a few distinct use cases related to that, they are relatively
> > hard to get right in a driver (if one wants to address all of them
> > properly) and it only gets worse if multiplied by the number of
> > drivers potentially needing to do it. Morever, at least one case
> > (asynchronous system suspend/resume) cannot be handled in a single
> > driver at all, because it requires the driver of A to wait for B to
> > suspend (during system suspend) and the driver of B to wait for
> > A to resume (during system resume).
> >
> > To that end, represent links between devices (or more precisely
> > between device+driver combos) as a struct device_link object
> > containing pointers to the devices in question, a list node for
> > each of them, status information, flags, a lock and an RCU head
> > for synchronization.
> >
> > Also add two new list heads, links_to_consumers and links_to_suppliers,
> > to struct device to represent the lists of links to the devices that
> > depend on the given one (consumers) and to the devices depended on
> > by it (suppliers), respectively.
> >
> > The entire data structure consisting of all of the lists of link
> > objects for all devices is protected by SRCU (for list walking)
> > and a by mutex (for link object addition/removal). In addition
> > to that, each link object has an internal status field whose
> > value reflects what's happening to the devices pointed to by
> > the link. That status field is protected by an internal spinlock.
> >
> > New links are added by calling device_link_add() which may happen
> > either before the consumer device is probed or when probing it, in
> > which case the caller must ensure that the driver of the supplier
> > device is present and functional and the DEVICE_LINK_SUPPLIER_READY
> > flag must be passed to device_link_add() to reflect that.
> >
> > Link objects are deleted either explicitly, by calling
> > device_link_del() on the link object in question, or automatically,
> > when the consumer device is unbound from its driver or when one
> > of the target devices is deleted, depending on the link type.
> >
> > There are two types of link objects, persistent and non-persistent.
> > The persistent ones stay around until one of the target devices is
> > deleted, while the non-persistent ones are deleted when the consumer
> > driver is unbound from its device (ie. they are assumed to be valid
> > only as long as the consumer device has a driver bound to it). The
> > DEVICE_LINK_PERSISTENT flag is passed to device_link_add() to create
> > a persistent link and it cannot be used for links created at the
> > consumer probe time (that is, persistent links must be created before
> > probing the consumer devices).
> >
> > One of the actions carried out by device_link_add() is to reorder
> > the lists used for device shutdown and system suspend/resume to
> > put the consumer device along with all of its children and all of
> > its consumers (and so on, recursively) to the ends of those list
> > in order to ensure the right ordering between the all of the supplier
> > and consumer devices.
>
> Rafael, thanks for working on this and re-spinning this series. It's
> indeed very interesting!
Well, you're welcome. :-)
> I am hoping "device links" should be able to solve some of those
> device ordering issues I have observed for several SoCs, particularly
> during system PM and in combination with runtime PM.
>
> I intend to test the series as soon as I can and try to deploy it to
> see if it solves some of the issues I have seen. I will also try to
> review in more detail. No promises short term though. :-)
All feedback will be appreciated.
I think I'll send an update of it tomorrow, though.
> BTW, as I am mostly working on DT based platforms, I guess we would
> later on need to discuss with the DT maintainers how to describe
> device links.
>
> A minor comment to the change-log. I would appreciate some information
> about "error" handling. Especially, what happens in the driver core
> when it's about to probe a device with a configured device link, but
> the link hasn’t been established yet (the other device isn't
> successfully probed). In the ideal scenario this shouldn't happen, but
> of course it will. So I assume the driver core relies on the existing
> deferred probe mechanism for this.
Yes, it does. I'll update the changelog with this information.
Thanks,
Rafael
next prev parent reply other threads:[~2016-09-15 1:05 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 [this message]
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
[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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