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 v7 0/7] Solve postboot supplier cleanup and optimize probe ordering
Date: Thu, 25 Jul 2019 15:42:14 +0200 [thread overview]
Message-ID: <20190725134214.GD11115@kroah.com> (raw)
In-Reply-To: <20190724001100.133423-1-saravanak@google.com>
On Tue, Jul 23, 2019 at 05:10:53PM -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.
>
> v1 -> v2:
> - Drop patch to speed up of_find_device_by_node()
> - Drop depends-on property and use existing bindings
>
> v2 -> v3:
> - Refactor the code to have driver core initiate the linking of devs
> - Have driver core link consumers to supplier before it's probed
> - Add support for drivers to edit the device links before probing
>
> v3 -> v4:
> - Tested edit_links() on system with cyclic dependency. Works.
> - Added some checks to make sure device link isn't attempted from
> parent device node to child device node.
> - Added way to pause/resume sync_state callbacks across
> of_platform_populate().
> - Recursively parse DT node to create device links from parent to
> suppliers of parent and all child nodes.
>
> v4 -> v5:
> - Fixed copy-pasta bugs with linked list handling
> - Walk up the phandle reference till I find an actual device (needed
> for regulators to work)
> - Added support for linking devices from regulator DT bindings
> - Tested the whole series again to make sure cyclic dependencies are
> broken with edit_links() and regulator links are created properly.
>
> v5 -> v6:
> - Split, squashed and reordered some of the patches.
> - Refactored the device linking code to follow the same code pattern for
> any property.
>
> v6 -> v7:
> - No functional changes.
> - Renamed i to index
> - Added comment to clarify not having to check property name for every
> index
> - Added "matched" variable to clarify code. No functional change.
> - Added comments to include/linux/device.h for add_links()
>
> I've also not updated this patch series to handle the new patch [1] from
> Rafael. Will do that once this patch series is close to being Acked.
>
> [1] - https://lore.kernel.org/lkml/3121545.4lOhFoIcdQ@kreacher/
This looks sane to me. Anyone have any objections for me queueing this
up for my tree to get into linux-next now?
thanks,
greg k-h
next prev parent reply other threads:[~2019-07-25 13:42 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-24 0:10 [PATCH v7 0/7] Solve postboot supplier cleanup and optimize probe ordering Saravana Kannan
2019-07-24 0:10 ` [PATCH v7 1/7] driver core: Add support for linking devices during device addition Saravana Kannan
2019-08-08 2:04 ` Frank Rowand
2019-08-16 1:50 ` Saravana Kannan
2019-08-19 3:38 ` Frank Rowand
2019-08-20 0:00 ` Saravana Kannan
2019-08-20 4:25 ` Frank Rowand
2019-08-20 22:10 ` Saravana Kannan
2019-08-21 1:06 ` Frank Rowand
2019-08-21 1:56 ` Greg Kroah-Hartman
2019-08-21 2:01 ` Saravana Kannan
2019-08-21 4:24 ` Frank Rowand
2019-08-21 2:04 ` Saravana Kannan
2019-08-21 2:22 ` Saravana Kannan
2019-08-21 15:36 ` Frank Rowand
2019-07-24 0:10 ` [PATCH v7 2/7] driver core: Add edit_links() callback for drivers Saravana Kannan
2019-08-08 2:05 ` Frank Rowand
2019-08-16 1:50 ` Saravana Kannan
2019-07-24 0:10 ` [PATCH v7 3/7] of/platform: Add functional dependency link from DT bindings Saravana Kannan
2019-08-08 2:06 ` Frank Rowand
2019-08-16 1:50 ` Saravana Kannan
2019-08-19 17:16 ` Frank Rowand
2019-08-19 20:49 ` Saravana Kannan
2019-08-19 21:30 ` Frank Rowand
2019-08-20 0:09 ` Saravana Kannan
2019-08-20 4:26 ` Frank Rowand
2019-08-20 22:09 ` Saravana Kannan
2019-08-21 16:39 ` Frank Rowand
2019-07-24 0:10 ` [PATCH v7 4/7] driver core: Add sync_state driver/bus callback Saravana Kannan
2019-07-24 0:10 ` [PATCH v7 5/7] of/platform: Pause/resume sync state during init and of_platform_populate() Saravana Kannan
2019-07-24 0:10 ` [PATCH v7 6/7] of/platform: Create device links for all child-supplier depencencies Saravana Kannan
2019-07-24 0:11 ` [PATCH v7 7/7] of/platform: Don't create device links for default busses Saravana Kannan
2019-07-25 13:42 ` Greg Kroah-Hartman [this message]
2019-07-25 21:04 ` [PATCH v7 0/7] Solve postboot supplier cleanup and optimize probe ordering Frank Rowand
2019-07-26 14:32 ` Greg Kroah-Hartman
2019-07-31 2:22 ` Frank Rowand
2019-08-08 2:02 ` 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=20190725134214.GD11115@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).