From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Saravana Kannan <saravanak@google.com>
Cc: Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Frank Rowand <frowand.list@gmail.com>,
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 08:12:09 +0200 [thread overview]
Message-ID: <20190801061209.GA3570@kroah.com> (raw)
In-Reply-To: <20190731221721.187713-1-saravanak@google.com>
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.
thanks for sticking with this!
greg k-h
next prev parent reply other threads:[~2019-08-01 6:12 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 ` Greg Kroah-Hartman [this message]
2019-08-01 19:28 ` [PATCH v9 0/7] Solve postboot supplier cleanup and optimize probe ordering Frank Rowand
2019-08-01 19:32 ` Greg Kroah-Hartman
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190801061209.GA3570@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=collinsd@codeaurora.org \
--cc=devicetree@vger.kernel.org \
--cc=frowand.list@gmail.com \
--cc=kernel-team@android.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=rafael@kernel.org \
--cc=robh+dt@kernel.org \
--cc=saravanak@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).