From: Frank Rowand <frowand.list@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Saravana Kannan <saravanak@google.com>
Cc: 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 v7 0/7] Solve postboot supplier cleanup and optimize probe ordering
Date: Thu, 25 Jul 2019 14:04:23 -0700 [thread overview]
Message-ID: <99ca3252-55af-8eea-7653-8347b0a1ab03@gmail.com> (raw)
In-Reply-To: <20190725134214.GD11115@kroah.com>
On 7/25/19 6:42 AM, Greg Kroah-Hartman wrote:
> 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?
I would like for the series to get into linux-next sooner than later,
and spend some time there.
I am _slightly_ more optimistic than Rob that sitting in linux-next for
an extended period might reveal any latent issues, so I would like for
the series to be in linux-next for an extended period of time. (Yes,
my understanding is that Linus does not like patches to be in linux-next
if they are not targeted for the next merge window, but I prefer that
this patch series spend as much time in linux-next as possible).
I have been waiting for the changes to settle down before bringing up
the issue of devicetree overlays. Now that the code seems to be
settling down, I need to look at how these changes impact overlays.
So I do not think the patches will be ready for a Linus pull request
until overlays are considered.
-Frank
>
> thanks,
>
> greg k-h
>
next prev parent reply other threads:[~2019-07-25 21:04 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 ` [PATCH v7 0/7] Solve postboot supplier cleanup and optimize probe ordering Greg Kroah-Hartman
2019-07-25 21:04 ` Frank Rowand [this message]
2019-07-26 14:32 ` Greg Kroah-Hartman
2019-07-31 2:22 ` Frank Rowand
2019-08-08 2:02 ` Frank Rowand
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