[PATCH v2 02/13] drivers: base: Add generic dma context bus

Vishnu Reddy
2026-04-23T13:30:16Z

From: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>

When a driver needs to create virtual device at runtime and map it to
an IOMMU context for memory isolation, there is no common bus available
for this purpose. Each driver ends up implementing its own bus type,
leading to duplicated logic across multiple drivers.

host1x driver implemented its own bus type to attach an IOMMU context to
a dynamically created device. The Iris VPU driver now has the same
requirement. Rather than duplicating the same bus logic again, a shared
bus type is introduced under drivers/base that multiple drivers can use
directly.

The bus takes care of creating a device and attaching the IOMMU context
to it based on the client inputs.

Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
Signed-off-by: Vikash Garodia <vikash.garodia@oss.qualcomm.com>
Signed-off-by: Vishnu Reddy <busanna.reddy@oss.qualcomm.com>
---
drivers/base/Kconfig | 3 ++
drivers/base/Makefile | 1 +
drivers/base/dma_context_bus.c | 77 +++++++++++++++++++++++++++++++++++++++++
include/linux/dma_context_bus.h | 26 ++++++++++++++
4 files changed, 107 insertions(+)

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index f7d385cbd3ba..499ea92dd88f 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -4,6 +4,9 @@ menu "Generic Driver Options"
config AUXILIARY_BUS
bool

+config DMA_CONTEXT_BUS
+ bool
+
config UEVENT_HELPER
bool "Support for uevent helper"
help
diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 8074a10183dc..348e69695e55 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -8,6 +8,7 @@ obj-y := component.o core.o bus.o dd.o syscore.o \
topology.o container.o property.o cacheinfo.o \
swnode.o faux.o
obj-$(CONFIG_AUXILIARY_BUS) += auxiliary.o
+obj-$(CONFIG_DMA_CONTEXT_BUS) += dma_context_bus.o
obj-$(CONFIG_DEVTMPFS) += devtmpfs.o
obj-y += power/
obj-$(CONFIG_ISA_BUS_API) += isa.o
diff --git a/drivers/base/dma_context_bus.c b/drivers/base/dma_context_bus.c
new file mode 100644
index 000000000000..c2ac189ce08d
--- /dev/null
+++ b/drivers/base/dma_context_bus.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+#include <linux/dma_context_bus.h>
+#include <linux/of_device.h>
+
+static atomic_t dma_context_bus_device_id = ATOMIC_INIT(0);
+
+static int dma_context_bus_device_configure(struct device *dev)
+{
+ const u32 *iommu_fid = dev_get_drvdata(dev);
+ struct device_node *of_node = dev->of_node;
+
+ if (!of_node)
+ of_node = dev->parent->of_node;
+
+ return of_dma_configure_id(dev, of_node, true, iommu_fid);
+}
+
+const struct bus_type dma_context_bus_type = {
+ .name = "dma-context-bus",
+ .dma_configure = dma_context_bus_device_configure,
+};
+EXPORT_SYMBOL_GPL(dma_context_bus_type);
+
+static void release_dma_context_bus_device(struct device *dev)
+{
+ kfree(dev);
+}
+
+struct device *create_dma_context_bus_device(struct device *parent_device,
+ struct device_node *of_node,
+ u64 dma_mask, const u32 *iommu_fid)
+{
+ struct device *dev;
+ int dev_id, ret;
+
+ dev = kzalloc_obj(*dev);
+ if (!dev)
+ return ERR_PTR(-ENOMEM);
+
+ dev->release = release_dma_context_bus_device;
+ dev->bus = &dma_context_bus_type;
+ dev->parent = parent_device;
+ dev->coherent_dma_mask = dma_mask;
+ dev->dma_mask = &dev->coherent_dma_mask;
+ dev->of_node = of_node;
+
+ dev_id = atomic_inc_return(&dma_context_bus_device_id);
+ dev_set_name(dev, "dma-context-bus-%d", dev_id);
+ dev_set_drvdata(dev, (void *)iommu_fid);
+
+ ret = device_register(dev);
+ if (ret) {
+ put_device(dev);
+ return ERR_PTR(ret);
+ }
+
+ return dev;
+}
+EXPORT_SYMBOL_GPL(create_dma_context_bus_device);
+
+static int __init dma_context_bus_init(void)
+{
+ int err;
+
+ err = bus_register(&dma_context_bus_type);
+ if (err) {
+ pr_err("dma-context-bus registration failed: %d\n", err);
+ return err;
+ }
+
+ return 0;
+}
+postcore_initcall(dma_context_bus_init);
diff --git a/include/linux/dma_context_bus.h b/include/linux/dma_context_bus.h
new file mode 100644
index 000000000000..3d89594fbce4
--- /dev/null
+++ b/include/linux/dma_context_bus.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+#ifndef _LINUX_DMA_CONTEXT_BUS_H
+#define _LINUX_DMA_CONTEXT_BUS_H
+
+#include <linux/device.h>
+
+#ifdef CONFIG_DMA_CONTEXT_BUS
+extern const struct bus_type dma_context_bus_type;
+
+struct device *create_dma_context_bus_device(struct device *parent_device,
+ struct device_node *of_node,
+ u64 dma_mask, const u32 *iommu_f_id);
+#else
+static inline struct device *create_dma_context_bus_device(struct device *parent_device,
+ struct device_node *of_node,
+ u64 dma_mask, const u32 *iommu_f_id)
+{
+ return NULL;
+}
+#endif
+
+#endif /* _LINUX_DMA_CONTEXT_BUS_H */

--
2.34.1