[PATCH v5 05/14] amba: Add driver dma ownership management

[Lu Baolu]

Multiple amba devices may be placed in the same IOMMU group because
they cannot be isolated from each other. These devices must either be
entirely under kernel control or userspace control, never a mixture. This
checks and sets DMA ownership during driver binding, and release the
ownership during driver unbinding.

The device driver may set a new flag (no_kernel_api_dma) to skip calling
iommu_device_use_dma_api() during the binding process. For instance, the
userspace framework drivers (vfio etc.) which need to manually claim
their own dma ownership when assigning the device to userspace.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 include/linux/amba/bus.h |  1 +
 drivers/amba/bus.c       | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/amba/bus.h b/include/linux/amba/bus.h
index edfcf7a14dcd..a4f374e2fd35 100644
--- a/include/linux/amba/bus.h
+++ b/include/linux/amba/bus.h
@@ -79,6 +79,7 @@ struct amba_driver {
 	void			(*remove)(struct amba_device *);
 	void			(*shutdown)(struct amba_device *);
 	const struct amba_id	*id_table;
+	bool no_kernel_api_dma;
 };
 
 /*
diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 850a0a8973c6..42b20ecfa50c 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -22,6 +22,7 @@
 #include <linux/of_irq.h>
 #include <linux/of_device.h>
 #include <linux/acpi.h>
+#include <linux/iommu.h>
 
 #include <asm/irq.h>
 
@@ -255,9 +256,16 @@ static void amba_shutdown(struct device *dev)
 
 static int amba_dma_configure(struct device *dev)
 {
+	struct amba_driver *drv = to_amba_driver(dev->driver);
 	enum dev_dma_attr attr;
 	int ret = 0;
 
+	if (!drv->no_kernel_api_dma) {
+		ret = iommu_device_use_dma_api(dev);
+		if (ret)
+			return ret;
+	}
+
 	if (dev->of_node) {
 		ret = of_dma_configure(dev, dev->of_node, true);
 	} else if (has_acpi_companion(dev)) {
@@ -265,9 +273,20 @@ static int amba_dma_configure(struct device *dev)
 		ret = acpi_dma_configure(dev, attr);
 	}
 
+	if (ret && !drv->no_kernel_api_dma)
+		iommu_device_unuse_dma_api(dev);
+
 	return ret;
 }
 
+static void amba_dma_cleanup(struct device *dev)
+{
+	struct amba_driver *drv = to_amba_driver(dev->driver);
+
+	if (!drv->no_kernel_api_dma)
+		iommu_device_unuse_dma_api(dev);
+}
+
 #ifdef CONFIG_PM
 /*
  * Hooks to provide runtime PM of the pclk (bus clock).  It is safe to
@@ -337,6 +356,7 @@ struct bus_type amba_bustype = {
 	.remove		= amba_remove,
 	.shutdown	= amba_shutdown,
 	.dma_configure	= amba_dma_configure,
+	.dma_cleanup	= amba_dma_cleanup,
 	.pm		= &amba_pm,
 };
 EXPORT_SYMBOL_GPL(amba_bustype);
-- 
2.25.1