[PATCH v4 3/7] iommu: register the DMA channel bus for IOMMU notifications

["Peng Fan (OSS)" <peng.fan@oss.nxp.com>]

From: Peng Fan <peng.fan@nxp.com>

DMA channel devices are about to be registered on a dedicated DMA channel
bus so that they get a properly balanced bus association before
device_register().

Add that bus to iommu_buses[] so the IOMMU core installs its bus notifier
for it. This allows of_dma_configure() to probe a per-channel IOMMU and,
more importantly, lets BUS_NOTIFY_REMOVED_DEVICE release the IOMMU group
and domain when the channel device is unregistered.

The dmaengine bus is registered from a core_initcall, before any IOMMU
driver can call iommu_device_register(), which iterates iommu_buses[] and
fails if a bus has not been registered yet. Guard the entry with
CONFIG_DMA_ENGINE because the bus does not exist when the DMA engine core
is not built.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 drivers/iommu/iommu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index b486b8bbd1fcd..6fa871bbd63ad 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -8,6 +8,7 @@
 
 #include <linux/amba/bus.h>
 #include <linux/device.h>
+#include <linux/dmaengine.h>
 #include <linux/kernel.h>
 #include <linux/bits.h>
 #include <linux/bug.h>
@@ -191,6 +192,9 @@ static const struct bus_type * const iommu_buses[] = {
 #ifdef CONFIG_ARM_AMBA
 	&amba_bustype,
 #endif
+#ifdef CONFIG_DMA_ENGINE
+	&dma_chan_bus_type,
+#endif
 #ifdef CONFIG_FSL_MC_BUS
 	&fsl_mc_bus_type,
 #endif

-- 
2.34.1