linux-kernel - [PATCH 1/3] staging: vme: add functions for bridge module refcounting

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Message-ID: <1314608570-32766-2-git-send-email-manohar.vanga@cern.ch>
Date:	Mon, 29 Aug 2011 11:02:48 +0200
From:	Manohar Vanga <manohar.vanga@...n.ch>
To:	<gregkh@...e.de>
CC:	<martyn.welch@...com>, <cota@...ap.org>,
	<devel@...verdev.osuosl.org>, <linux-kernel@...r.kernel.org>,
	Manohar Vanga <manohar.vanga@...n.ch>
Subject: [PATCH 1/3] staging: vme: add functions for bridge module refcounting

This patch adds functions that allow for reference counting
bridge modules. The patch introduces the functions
'vme_bridge_get()' and 'vme_bridge_put()'.

The functions are automatically called during .probe and .remove
for drivers.

This patch is based on the changes introduced by Emilio G. Cota
in the patch:

    https://lkml.org/lkml/2010/10/25/492

Signed-off-by: Manohar Vanga <manohar.vanga@...n.ch>
---
 drivers/staging/vme/bridges/vme_ca91cx42.c |    2 +
 drivers/staging/vme/bridges/vme_tsi148.c   |    2 +
 drivers/staging/vme/vme.c                  |   43 +++++++++++++++++++++++++--
 drivers/staging/vme/vme_bridge.h           |    1 +
 4 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/vme/bridges/vme_ca91cx42.c b/drivers/staging/vme/bridges/vme_ca91cx42.c
index 0e4feac..b80cb12 100644
--- a/drivers/staging/vme/bridges/vme_ca91cx42.c
+++ b/drivers/staging/vme/bridges/vme_ca91cx42.c
@@ -1673,6 +1673,8 @@ static int ca91cx42_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	ca91cx42_bridge->parent = &pdev->dev;
 	strcpy(ca91cx42_bridge->name, driver_name);
 
+	ca91cx42_bridge->owner = THIS_MODULE;
+
 	/* Setup IRQ */
 	retval = ca91cx42_irq_init(ca91cx42_bridge);
 	if (retval != 0) {
diff --git a/drivers/staging/vme/bridges/vme_tsi148.c b/drivers/staging/vme/bridges/vme_tsi148.c
index 6c1167c..b0b434a 100644
--- a/drivers/staging/vme/bridges/vme_tsi148.c
+++ b/drivers/staging/vme/bridges/vme_tsi148.c
@@ -2312,6 +2312,8 @@ static int tsi148_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	tsi148_bridge->parent = &pdev->dev;
 	strcpy(tsi148_bridge->name, driver_name);
 
+	tsi148_bridge->owner = THIS_MODULE;
+
 	/* Setup IRQ */
 	retval = tsi148_irq_init(tsi148_bridge);
 	if (retval != 0) {
diff --git a/drivers/staging/vme/vme.c b/drivers/staging/vme/vme.c
index feb2d00..f5ff578 100644
--- a/drivers/staging/vme/vme.c
+++ b/drivers/staging/vme/vme.c
@@ -52,6 +52,32 @@ static struct vme_bridge *dev_to_bridge(struct device *dev)
 }
 
 /*
+ * Increments the reference count of a VME bridge.
+ *
+ * On success, it can be assumed that the bridge won't be removed until
+ * the corresponding call to vme_put_bridge(). This along with
+ * vme_bridge_put are automatically called and VME device drivers need
+ * not worry about using this.
+ */
+static int vme_bridge_get(struct vme_bridge *bridge)
+{
+	if (try_module_get(bridge->owner))
+		return 0;
+	return -ENXIO;
+}
+
+/*
+ * Decrements the reference count of a VME bridge
+ *
+ * This function decrements the reference count of the module that controls
+ * the bridge. It must come after a call to vme_bridge_get().
+ */
+static void vme_bridge_put(struct vme_bridge *bridge)
+{
+	module_put(bridge->owner);
+}
+
+/*
  * Find the bridge that the resource is associated with.
  */
 static struct vme_bridge *find_bridge(struct vme_resource *resource)
@@ -1496,13 +1522,19 @@ static int vme_bus_probe(struct device *dev)
 {
 	struct vme_bridge *bridge;
 	struct vme_driver *driver;
-	int retval = -ENODEV;
+	int retval = 0;
 
 	driver = dev_to_vme_driver(dev);
 	bridge = dev_to_bridge(dev);
 
-	if (driver->probe != NULL)
+	if (driver->probe) {
+		if (vme_bridge_get(bridge))
+			return -ENXIO;
+
 		retval = driver->probe(dev, bridge->num, vme_calc_slot(dev));
+		if (retval)
+			vme_bridge_put(bridge);
+	}
 
 	return retval;
 }
@@ -1511,14 +1543,17 @@ static int vme_bus_remove(struct device *dev)
 {
 	struct vme_bridge *bridge;
 	struct vme_driver *driver;
-	int retval = -ENODEV;
+	int retval = 0;
 
 	driver = dev_to_vme_driver(dev);
 	bridge = dev_to_bridge(dev);
 
-	if (driver->remove != NULL)
+	if (driver->remove)
 		retval = driver->remove(dev, bridge->num, vme_calc_slot(dev));
 
+	if (driver->probe)
+		vme_bridge_put(bridge);
+
 	return retval;
 }
 
diff --git a/drivers/staging/vme/vme_bridge.h b/drivers/staging/vme/vme_bridge.h
index 8959670..ef751a4 100644
--- a/drivers/staging/vme/vme_bridge.h
+++ b/drivers/staging/vme/vme_bridge.h
@@ -113,6 +113,7 @@ struct vme_bridge {
 	struct device *parent;	/* Parent device (eg. pdev->dev for PCI) */
 	void *driver_priv;	/* Private pointer for the bridge driver */
 	struct list_head bus_list; /* list of VME buses */
+	struct module *owner;	/* module that owns the bridge */
 
 	struct device dev[VME_SLOTS_MAX];	/* Device registered with
 						 * device model on VME bus
-- 
1.7.4.1

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