[PATCH 4/6] staging: vme: add functions for bridge module refcounting

[Manohar Vanga]

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 at cern.ch>
---
 drivers/staging/vme/bridges/vme_ca91cx42.c |    2 +
 drivers/staging/vme/bridges/vme_tsi148.c   |    2 +
 drivers/staging/vme/vme.c                  |   54 ++++++++++++++++++++++++++++
 drivers/staging/vme/vme.h                  |    2 +
 drivers/staging/vme/vme_bridge.h           |    1 +
 5 files changed, 61 insertions(+), 0 deletions(-)

diff --git a/drivers/staging/vme/bridges/vme_ca91cx42.c b/drivers/staging/vme/bridges/vme_ca91cx42.c
index 15a0b19..2f9c22b 100644
--- a/drivers/staging/vme/bridges/vme_ca91cx42.c
+++ b/drivers/staging/vme/bridges/vme_ca91cx42.c
@@ -1680,6 +1680,8 @@ 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 5c147d6..9db89dc 100644
--- a/drivers/staging/vme/bridges/vme_tsi148.c
+++ b/drivers/staging/vme/bridges/vme_tsi148.c
@@ -2320,6 +2320,8 @@ 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 f811d07..0504007 100644
--- a/drivers/staging/vme/vme.c
+++ b/drivers/staging/vme/vme.c
@@ -52,6 +52,54 @@ static struct vme_bridge *dev_to_bridge(struct device *dev)
 }
 
 /*
+ * Increments the reference count of a VME bridge.
+ *
+ * If found, a pointer to the bridge is returned and the reference count
+ * of the module that owns it is incremented.
+ *
+ * On success, it can be assumed that the bridge won't be removed until
+ * the corresponding call to vme_put_bridge().
+ *
+ * Normally drivers should call vme_get_bridge() on a successfull .probe,
+ * and vme_put_bridge() when releasing the device, e.g. in .remove.
+ */
+struct vme_bridge *vme_bridge_get(unsigned int bus_id)
+{
+	struct vme_bridge *bridge;
+	struct vme_bridge *retp = NULL;
+
+	mutex_lock(&vme_buses_lock);
+	list_for_each_entry(bridge, &vme_bus_list, bus_list) {
+		if (bridge->num == bus_id) {
+			if (!bridge->owner)
+				dev_warn(bridge->parent,
+					"bridge->owner not set\n");
+			else if (try_module_get(bridge->owner))
+				retp = bridge;
+			break;
+		}
+	}
+	mutex_unlock(&vme_buses_lock);
+	return retp;
+}
+EXPORT_SYMBOL(vme_bridge_get);
+
+/*
+ * Decrements the reference count of a bridge
+ *
+ * This function decrements the reference count of the module that controls
+ * the bridge. It must come after a call to vme_get_bridge().
+ */
+void vme_bridge_put(struct vme_bridge *bridge)
+{
+	if (!bridge->owner)
+		dev_warn(bridge->parent, "bridge->owner not set\n");
+	else
+		module_put(bridge->owner);
+}
+EXPORT_SYMBOL(vme_bridge_put);
+
+/*
  * Find the bridge that the resource is associated with.
  */
 static struct vme_bridge *find_bridge(struct vme_resource *resource)
@@ -1525,9 +1573,13 @@ static int vme_bus_probe(struct device *dev)
 	driver = dev_to_vme_driver(dev);
 	bridge = dev_to_bridge(dev);
 
+	vme_bridge_get(bridge->num);
 	if (driver->probe != NULL)
 		retval = driver->probe(dev, bridge->num, vme_calc_slot(dev));
 
+	if (retval)
+		vme_bridge_put(bridge);
+
 	return retval;
 }
 
@@ -1543,6 +1595,8 @@ static int vme_bus_remove(struct device *dev)
 	if (driver->remove != NULL)
 		retval = driver->remove(dev, bridge->num, vme_calc_slot(dev));
 
+	vme_bridge_put(bridge);
+
 	return retval;
 }
 
diff --git a/drivers/staging/vme/vme.h b/drivers/staging/vme/vme.h
index 3ccb497..8fb35e2 100644
--- a/drivers/staging/vme/vme.h
+++ b/drivers/staging/vme/vme.h
@@ -167,6 +167,8 @@ int vme_slot_get(struct device *);
 int vme_register_driver(struct vme_driver *);
 void vme_unregister_driver(struct vme_driver *);
 
+struct vme_bridge *vme_bridge_get(unsigned int bus_id);
+void vme_bridge_put(struct vme_bridge *bridge);
 
 #endif /* _VME_H_ */
 
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