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From: Saravana Kannan <saravanak@google.com>
To: Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Jonathan Corbet <corbet@lwn.net>, Len Brown <lenb@kernel.org>
Cc: Saravana Kannan <saravanak@google.com>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-acpi@vger.kernel.org,
	clang-built-linux@googlegroups.com,
	David Collins <collinsd@codeaurora.org>,
	kernel-team@android.com
Subject: [PATCH v11 6/6] of: property: Create device links for all child-supplier depencencies
Date: Wed,  4 Sep 2019 14:11:25 -0700	[thread overview]
Message-ID: <20190904211126.47518-7-saravanak@google.com> (raw)
In-Reply-To: <20190904211126.47518-1-saravanak@google.com>

A parent device can have child devices that it adds when it probes. But
this probing of the parent device can happen way after kernel init is done
-- for example, when the parent device's driver is loaded as a module.

In such cases, if the child devices depend on a supplier in the system, we
need to make sure the supplier gets the sync_state() callback only after
these child devices are added and probed.

To achieve this, when creating device links for a device by looking at its
DT node, don't just look at DT references at the top node level. Look at DT
references in all the descendant nodes too and create device links from the
ancestor device to all these supplier devices.

This way, when the parent device probes and adds child devices, the child
devices can then create their own device links to the suppliers and further
delay the supplier's sync_state() callback to after the child devices are
probed.

Example:
In this illustration, -> denotes DT references and indentation
represents child status.

Device node A
	Device node B -> D
	Device node C -> B, D

Device node D

Assume all these devices have their drivers loaded as modules.

Without this patch, this is the sequence of events:
1. D is added.
2. A is added.
3. Device D probes.
4. Device D gets its sync_state() callback.
5. Device B and C might malfunction because their resources got
   altered/turned off before they can make active requests for them.

With this patch, this is the sequence of events:
1. D is added.
2. A is added and creates device links to D.
3. Device link from A to B is not added because A is a parent of B.
4. Device D probes.
5. Device D does not get it's sync_state() callback because consumer A
   hasn't probed yet.
5. Device A probes.
5. a. Devices B and C are added.
5. b. Device links from B and C to D are added.
5. c. Device A's probe completes.
6. Device D does not get it's sync_state() callback because consumer A
   has probed but consumers B and C haven't probed yet.
7. Device B and C probe.
8. Device D gets it's sync_state() callback because all its consumers
   have probed.
9. None of the devices malfunction.

Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 drivers/of/property.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index 23b5ee5b0570..923d6f88a99c 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c
@@ -1207,6 +1207,10 @@ static int __of_link_to_suppliers(struct device *dev,
 		if (of_link_property(dev, con_np, p->name))
 			ret = -EAGAIN;
 
+	for_each_child_of_node(con_np, child)
+		if (__of_link_to_suppliers(dev, child))
+			ret = -EAGAIN;
+
 	return ret;
 }
 
-- 
2.23.0.187.g17f5b7556c-goog


  parent reply	other threads:[~2019-09-04 21:11 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 ` Saravana Kannan [this message]
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

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