[RFC] fpga: region: Move spinlock for bridge_list into region

[Moritz Fischer <mdf@kernel.org>]

Instead of using a single (global) spinlock for all bridge lists use a
spinlock per list inside the containing fpga region.

Signed-off-by: Moritz Fischer <mdf@kernel.org>
---

Hi all,

maybe I do misunderstand something fundamental here ;-) In that case,
please explain. In my understanding the current version works, because
it is more defensive, but is there a reason we need to make access to
any of the bridge lists exclusive?

Cheers,
Moritz

PS: Not fully happy with this patch, but wanted to figure out first if
this I'm wrong conceptually

---
 drivers/fpga/fpga-bridge.c | 5 ++---
 drivers/fpga/fpga-region.c | 6 ++++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/fpga/fpga-bridge.c b/drivers/fpga/fpga-bridge.c
index 9651aa56244a..b03ec59448e2 100644
--- a/drivers/fpga/fpga-bridge.c
+++ b/drivers/fpga/fpga-bridge.c
@@ -214,6 +214,8 @@ EXPORT_SYMBOL_GPL(fpga_bridges_put);
  *
  * Get an exclusive reference to the bridge and and it to the list.
  *
+ * Must be called with list lock held.
+ *
  * Return 0 for success, error code from of_fpga_bridge_get() othewise.
  */
 int fpga_bridge_get_to_list(struct device_node *np,
@@ -221,15 +223,12 @@ int fpga_bridge_get_to_list(struct device_node *np,
 			    struct list_head *bridge_list)
 {
 	struct fpga_bridge *bridge;
-	unsigned long flags;
 
 	bridge = of_fpga_bridge_get(np, info);
 	if (IS_ERR(bridge))
 		return PTR_ERR(bridge);
 
-	spin_lock_irqsave(&bridge_list_lock, flags);
 	list_add(&bridge->node, bridge_list);
-	spin_unlock_irqrestore(&bridge_list_lock, flags);
 
 	return 0;
 }
diff --git a/drivers/fpga/fpga-region.c b/drivers/fpga/fpga-region.c
index 3b6b2f4182a1..c5c958e0e601 100644
--- a/drivers/fpga/fpga-region.c
+++ b/drivers/fpga/fpga-region.c
@@ -37,6 +37,7 @@ struct fpga_region {
 	struct device dev;
 	struct mutex mutex; /* for exclusive reference to region */
 	struct list_head bridge_list;
+	spinlock_t bridge_list_lock; /* protects access to bridge list */
 	struct fpga_image_info *info;
 };
 
@@ -180,11 +181,15 @@ static int fpga_region_get_bridges(struct fpga_region *region,
 	struct device *dev = &region->dev;
 	struct device_node *region_np = dev->of_node;
 	struct device_node *br, *np, *parent_br = NULL;
+	unsigned long flags;
 	int i, ret;
 
 	/* If parent is a bridge, add to list */
+	spin_lock_irqsave(&region->bridge_list_lock, flags);
 	ret = fpga_bridge_get_to_list(region_np->parent, region->info,
 				      &region->bridge_list);
+	spin_unlock_irqrestore(&region->bridge_list_lock, flags);
+
 	if (ret == -EBUSY)
 		return ret;
 
@@ -508,6 +513,7 @@ static int fpga_region_probe(struct platform_device *pdev)
 
 	mutex_init(&region->mutex);
 	INIT_LIST_HEAD(&region->bridge_list);
+	spin_lock_init(&region->bridge_list_lock);
 
 	device_initialize(&region->dev);
 	region->dev.class = fpga_region_class;
-- 
2.14.1