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From: Greg Kroah-Hartman <>
To: Saravana Kannan <>
Cc: Rob Herring <>,
	Mark Rutland <>,
	"Rafael J. Wysocki" <>,
	Frank Rowand <>,
	Jonathan Corbet <>, Len Brown <>,,,,,,
	David Collins <>,
Subject: Re: [PATCH v11 0/6] Solve postboot supplier cleanup and optimize probe ordering
Date: Fri, 4 Oct 2019 17:34:14 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, Sep 04, 2019 at 02:11:19PM -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.

Hearing no real complaints again, I've now queued these up in my tree.


greg k-h

      parent reply	other threads:[~2019-10-04 15:34 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-04 21:11 [PATCH v11 0/6] Solve postboot supplier cleanup and optimize probe ordering Saravana Kannan
2019-09-04 21:11 ` [PATCH v11 1/6] driver core: Add fwnode_to_dev() to look up device from fwnode Saravana Kannan
2019-09-04 21:11 ` [PATCH v11 2/6] driver core: Add support for linking devices during device addition Saravana Kannan
2019-09-04 21:11 ` [PATCH v11 3/6] of: property: Add functional dependency link from DT bindings Saravana Kannan
2019-09-11 10:29   ` Stephen Boyd
2019-10-04 15:37     ` Greg Kroah-Hartman
2019-10-04 23:46       ` Saravana Kannan
2019-10-08 14:53       ` Stephen Boyd
2019-10-08 18:57         ` Saravana Kannan
2019-10-16 20:15           ` Stephen Boyd
2019-09-04 21:11 ` [PATCH v11 4/6] driver core: Add sync_state driver/bus callback Saravana Kannan
2019-09-04 21:11 ` [PATCH v11 5/6] of/platform: Pause/resume sync state during init and of_platform_populate() Saravana Kannan
2019-09-04 21:11 ` [PATCH v11 6/6] of: property: Create device links for all child-supplier depencencies Saravana Kannan
2019-09-11 10:34 ` [PATCH v11 0/6] Solve postboot supplier cleanup and optimize probe ordering Stephen Boyd
2019-10-04 15:34 ` Greg Kroah-Hartman [this message]

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