linux-kernel - [PATCH v1 1/5] of/platform: Speed up of_find_device_by

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Date:   Thu, 23 May 2019 18:01:12 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
Cc:     Saravana Kannan <saravanak@...gle.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: [PATCH v1 1/5] of/platform: Speed up of_find_device_by_node()

Add a pointer from device tree node to the device created from it.
This allows us to find the device corresponding to a device tree node
without having to loop through all the platform devices.

However, fallback to looping through the platform devices to handle
any devices that might set their own of_node.

Signed-off-by: Saravana Kannan <saravanak@...gle.com>
---
 drivers/of/platform.c | 20 +++++++++++++++++++-
 include/linux/of.h    |  3 +++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 04ad312fd85b..1115a8d80a33 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -42,6 +42,8 @@ static int of_dev_node_match(struct device *dev, void *data)
 	return dev->of_node == data;
 }
 
+static DEFINE_SPINLOCK(of_dev_lock);
+
 /**
  * of_find_device_by_node - Find the platform_device associated with a node
  * @np: Pointer to device tree node
@@ -55,7 +57,18 @@ struct platform_device *of_find_device_by_node(struct device_node *np)
 {
 	struct device *dev;
 
-	dev = bus_find_device(&platform_bus_type, NULL, np, of_dev_node_match);
+	/*
+	 * Spinlock needed to make sure np->dev doesn't get freed between NULL
+	 * check inside and kref count increment inside get_device(). This is
+	 * achieved by grabbing the spinlock before setting np->dev = NULL in
+	 * of_platform_device_destroy().
+	 */
+	spin_lock(&of_dev_lock);
+	dev = get_device(np->dev);
+	spin_unlock(&of_dev_lock);
+	if (!dev)
+		dev = bus_find_device(&platform_bus_type, NULL, np,
+				      of_dev_node_match);
 	return dev ? to_platform_device(dev) : NULL;
 }
 EXPORT_SYMBOL(of_find_device_by_node);
@@ -196,6 +209,7 @@ static struct platform_device *of_platform_device_create_pdata(
 		platform_device_put(dev);
 		goto err_clear_flag;
 	}
+	np->dev = &dev->dev;
 
 	return dev;
 
@@ -556,6 +570,10 @@ int of_platform_device_destroy(struct device *dev, void *data)
 	if (of_node_check_flag(dev->of_node, OF_POPULATED_BUS))
 		device_for_each_child(dev, NULL, of_platform_device_destroy);
 
+	/* Spinlock is needed for of_find_device_by_node() to work */
+	spin_lock(&of_dev_lock);
+	dev->of_node->dev = NULL;
+	spin_unlock(&of_dev_lock);
 	of_node_clear_flag(dev->of_node, OF_POPULATED);
 	of_node_clear_flag(dev->of_node, OF_POPULATED_BUS);
 
diff --git a/include/linux/of.h b/include/linux/of.h
index 0cf857012f11..f2b4912cbca1 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -48,6 +48,8 @@ struct property {
 struct of_irq_controller;
 #endif
 
+struct device;
+
 struct device_node {
 	const char *name;
 	phandle phandle;
@@ -68,6 +70,7 @@ struct device_node {
 	unsigned int unique_id;
 	struct of_irq_controller *irq_trans;
 #endif
+	struct device *dev;		/* Device created from this node */
 };
 
 #define MAX_PHANDLE_ARGS 16
-- 
2.22.0.rc1.257.g3120a18244-goog