From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Frank Rowand <frowand.list@gmail.com>
Cc: Saravana Kannan <saravanak@google.com>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
David Collins <collinsd@codeaurora.org>,
kernel-team@android.com
Subject: Re: [PATCH v9 0/7] Solve postboot supplier cleanup and optimize probe ordering
Date: Thu, 1 Aug 2019 21:32:48 +0200 [thread overview]
Message-ID: <20190801193248.GA24916@kroah.com> (raw)
In-Reply-To: <5a1e785d-075e-19a0-7d3d-949e1b65d726@gmail.com>
On Thu, Aug 01, 2019 at 12:28:13PM -0700, Frank Rowand wrote:
> Hi Greg,
>
> On 7/31/19 11:12 PM, Greg Kroah-Hartman wrote:
> > On Wed, Jul 31, 2019 at 03:17:13PM -0700, Saravana Kannan wrote:
> >> Add device-links to track functional dependencies between devices
> >> after they are created (but before they are probed) by looking at
> >> their common DT bindings like clocks, interconnects, etc.
> >>
> >> Having functional dependencies automatically added before the devices
> >> are probed, provides the following benefits:
> >>
> >> - Optimizes device probe order and avoids the useless work of
> >> attempting probes of devices that will not probe successfully
> >> (because their suppliers aren't present or haven't probed yet).
> >>
> >> For example, in a commonly available mobile SoC, registering just
> >> one consumer device's driver at an initcall level earlier than the
> >> supplier device's driver causes 11 failed probe attempts before the
> >> consumer device probes successfully. This was with a kernel with all
> >> the drivers statically compiled in. This problem gets a lot worse if
> >> all the drivers are loaded as modules without direct symbol
> >> dependencies.
> >>
> >> - Supplier devices like clock providers, interconnect providers, etc
> >> need to keep the resources they provide active and at a particular
> >> state(s) during boot up even if their current set of consumers don't
> >> request the resource to be active. This is because the rest of the
> >> consumers might not have probed yet and turning off the resource
> >> before all the consumers have probed could lead to a hang or
> >> undesired user experience.
> >>
> >> Some frameworks (Eg: regulator) handle this today by turning off
> >> "unused" resources at late_initcall_sync and hoping all the devices
> >> have probed by then. This is not a valid assumption for systems with
> >> loadable modules. Other frameworks (Eg: clock) just don't handle
> >> this due to the lack of a clear signal for when they can turn off
> >> resources. This leads to downstream hacks to handle cases like this
> >> that can easily be solved in the upstream kernel.
> >>
> >> By linking devices before they are probed, we give suppliers a clear
> >> count of the number of dependent consumers. Once all of the
> >> consumers are active, the suppliers can turn off the unused
> >> resources without making assumptions about the number of consumers.
> >>
> >> By default we just add device-links to track "driver presence" (probe
> >> succeeded) of the supplier device. If any other functionality provided
> >> by device-links are needed, it is left to the consumer/supplier
> >> devices to change the link when they probe.
> >
> > All now queued up in my driver-core-testing branch, and if 0-day is
> > happy with this, will move it to my "real" driver-core-next branch in a
> > day or so to get included in linux-next.
>
> I have been slow in getting my review out.
>
> This patch series is not yet ready for sending to Linus, so if putting
> this in linux-next implies that it will be in your next pull request
> to Linus, please do not put it in linux-next.
It means that it will be in my pull request for 5.4-rc1, many many
waeeks away from now.
thanks,
greg k-h
next prev parent reply other threads:[~2019-08-01 19:32 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-31 22:17 [PATCH v9 0/7] Solve postboot supplier cleanup and optimize probe ordering Saravana Kannan
2019-07-31 22:17 ` [PATCH v9 1/7] driver core: Add support for linking devices during device addition Saravana Kannan
2019-07-31 22:17 ` [PATCH v9 2/7] driver core: Add edit_links() callback for drivers Saravana Kannan
2019-07-31 22:17 ` [PATCH v9 3/7] of/platform: Add functional dependency link from DT bindings Saravana Kannan
2019-07-31 22:17 ` [PATCH v9 4/7] driver core: Add sync_state driver/bus callback Saravana Kannan
2019-07-31 22:17 ` [PATCH v9 5/7] of/platform: Pause/resume sync state during init and of_platform_populate() Saravana Kannan
2019-07-31 22:17 ` [PATCH v9 6/7] of/platform: Create device links for all child-supplier depencencies Saravana Kannan
2019-07-31 22:17 ` [PATCH v9 7/7] of/platform: Don't create device links for default busses Saravana Kannan
2019-08-01 6:12 ` [PATCH v9 0/7] Solve postboot supplier cleanup and optimize probe ordering Greg Kroah-Hartman
2019-08-01 19:28 ` Frank Rowand
2019-08-01 19:32 ` Greg Kroah-Hartman [this message]
2019-08-01 19:59 ` Frank Rowand
2019-08-02 6:37 ` Greg Kroah-Hartman
2019-08-08 2:13 ` Frank Rowand
2019-08-27 19:43 ` Greg Kroah-Hartman
2019-08-10 2:57 ` Frank Rowand
2019-08-10 5:00 ` Saravana Kannan
2019-08-10 5:20 ` Frank Rowand
2019-08-16 1:50 ` Saravana Kannan
2019-08-16 3:09 ` Frank Rowand
2019-08-16 9:10 ` Greg Kroah-Hartman
2019-08-16 14:05 ` Frank Rowand
2019-08-16 15:23 ` Greg Kroah-Hartman
2019-08-16 20:52 ` Frank Rowand
2019-08-16 20:54 ` Frank Rowand
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