[PATCH] pseries/iommu: remove iommu device references via bus notifier

[Nishanth Aravamudan <nacc@linux.vnet.ibm.com>]

After d905c5df9aef ("PPC: POWERNV: move iommu_add_device earlier"), the
refcnt on the kobject backing the IOMMU group for a PCI device is
elevated by each call to pci_dma_dev_setup_pSeriesLP() (via
set_iommu_table_base_and_group). When we go to dlpar a multi-function
PCI device out:

	iommu_reconfig_notifier ->
		iommu_free_table ->
			iommu_group_put
			BUG_ON(tbl->it_group)

We trip this BUG_ON, because there are still references on the table, so
it is not freed. Fix this by also adding a bus notifier identical to
PowerNV for pSeries. Tested a remove -> add -> remove cycle without
issue where it always hit the BUG_ON without the changes.

Fixes: d905c5df9aef ("PPC: POWERNV: move iommu_add_device earlier")
Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Cc: stable@kernel.org (3.13+)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 1d3d52dc3ff3..f77fb02f4710 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1340,3 +1340,31 @@ static int __init disable_multitce(char *str)
 }
 
 __setup("multitce=", disable_multitce);
+
+static int tce_iommu_bus_notifier(struct notifier_block *nb,
+                unsigned long action, void *data)
+{
+        struct device *dev = data;
+
+        switch (action) {
+        case BUS_NOTIFY_ADD_DEVICE:
+                return iommu_add_device(dev);
+        case BUS_NOTIFY_DEL_DEVICE:
+                if (dev->iommu_group)
+                        iommu_del_device(dev);
+                return 0;
+        default:
+                return 0;
+        }
+}
+
+static struct notifier_block tce_iommu_bus_nb = {
+        .notifier_call = tce_iommu_bus_notifier,
+};
+
+static int __init tce_iommu_bus_notifier_init(void)
+{
+        bus_register_notifier(&pci_bus_type, &tce_iommu_bus_nb);
+        return 0;
+}
+machine_subsys_initcall_sync(pseries, tce_iommu_bus_notifier_init);