[PATCH] iommu/arm-smmu: add a shortcut when the @dev_node is NULL

From: Huang Shijie
Date: Mon Jan 11 2016 - 21:16:30 EST

When a device is added to a bus, it will trigger the chain notifier hook,
such as iommu_bus_notifier. The find_smmu_for_device() can be called here.

In some cases, the @device_node can be NULL. For example, when the device
is one of the following:
alarmtime, serial, rtc or snd_soc.

This patch adds a shortcut for the code when the @device_node is NULL.
In my juno-r1 board, the boot time can be faster by 0.004014s.

Signed-off-by: Huang Shijie <shijie.huang@xxxxxxx>
drivers/iommu/arm-smmu.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 59ee4b8..6724a46 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -506,6 +506,9 @@ static struct arm_smmu_device *find_smmu_for_device(struct device *dev)
struct arm_smmu_master *master = NULL;
struct device_node *dev_node = dev_get_dev_node(dev);

+ if (!dev_node)
+ return NULL;
list_for_each_entry(smmu, &arm_smmu_devices, list) {
master = find_smmu_master(smmu, dev_node);