On Tue, May 19, 2026 at 11:45:54AM +0530, Ekansh Gupta via B4 Relay wrote:
From: Ekansh Gupta ekansh.gupta@oss.qualcomm.com
Introduce a custom virtual bus (qda-compute-cb) for managing IOMMU context bank (CB) devices used by the QDA driver.
IOMMU context banks are synthetic constructs — they are not real platform devices and do not appear as children of a platform bus node in the device tree. Using a platform driver to represent them was therefore incorrect and introduced a probe-ordering race: device nodes were created before the RPMsg channel resources were fully initialized, and because probe runs asynchronously, user-space could open a CB device and attempt to start a session before the underlying transport was ready.
The qda-compute-cb bus solves this by allowing the main QDA driver to create CB devices explicitly and under its own control, making their lifetime strictly subordinate to the parent qda_dev. The bus provides a dma_configure callback that calls of_dma_configure() so that each CB device gets its own IOMMU domain derived from its device-tree node, enabling per-session memory isolation.
The bus type and the CB device constructor (create_qda_cb_device) are exported for use by the QDA memory manager.
A hidden Kconfig symbol (DRM_ACCEL_QDA_COMPUTE_BUS) is introduced and automatically selected by DRM_ACCEL_QDA so that the bus initialisation runs via postcore_initcall before any QDA device probes.
Assisted-by: Claude:claude-4-6-sonnet Signed-off-by: Ekansh Gupta ekansh.gupta@oss.qualcomm.com
drivers/accel/Makefile | 1 + drivers/accel/qda/Kconfig | 4 +++ drivers/accel/qda/Makefile | 2 ++ drivers/accel/qda/qda_compute_bus.c | 68 +++++++++++++++++++++++++++++++++++++ include/linux/qda_compute_bus.h | 32 +++++++++++++++++ 5 files changed, 107 insertions(+)
diff --git a/drivers/accel/Makefile b/drivers/accel/Makefile index 58c08dd5f389..9ed843cd293f 100644 --- a/drivers/accel/Makefile +++ b/drivers/accel/Makefile @@ -6,4 +6,5 @@ obj-$(CONFIG_DRM_ACCEL_HABANALABS) += habanalabs/ obj-$(CONFIG_DRM_ACCEL_IVPU) += ivpu/ obj-$(CONFIG_DRM_ACCEL_QAIC) += qaic/ obj-$(CONFIG_DRM_ACCEL_QDA) += qda/ +obj-$(CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS) += qda/
Ugh. The previous line should be enough (but don't trust me).
obj-$(CONFIG_DRM_ACCEL_ROCKET) += rocket/ \ No newline at end of file diff --git a/drivers/accel/qda/Kconfig b/drivers/accel/qda/Kconfig index 484d21ff1b55..2a61a4dda054 100644 --- a/drivers/accel/qda/Kconfig +++ b/drivers/accel/qda/Kconfig @@ -3,11 +3,15 @@ # Qualcomm DSP accelerator driver # +config DRM_ACCEL_QDA_COMPUTE_BUS
- bool
config DRM_ACCEL_QDA tristate "Qualcomm DSP accelerator" depends on DRM_ACCEL depends on ARCH_QCOM || COMPILE_TEST depends on RPMSG
- select DRM_ACCEL_QDA_COMPUTE_BUS help Enables the DRM-based accelerator driver for Qualcomm's Hexagon DSPs. This driver provides a standardized interface for offloading computational
diff --git a/drivers/accel/qda/Makefile b/drivers/accel/qda/Makefile index dbe809067a8b..424176f652a5 100644 --- a/drivers/accel/qda/Makefile +++ b/drivers/accel/qda/Makefile @@ -8,3 +8,5 @@ obj-$(CONFIG_DRM_ACCEL_QDA) := qda.o qda-y := \ qda_drv.o \ qda_rpmsg.o
+obj-$(CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS) += qda_compute_bus.o diff --git a/drivers/accel/qda/qda_compute_bus.c b/drivers/accel/qda/qda_compute_bus.c new file mode 100644 index 000000000000..c59d977e924d --- /dev/null +++ b/drivers/accel/qda/qda_compute_bus.c @@ -0,0 +1,68 @@ +// SPDX-License-Identifier: GPL-2.0-only +// Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries. +#include <linux/device.h> +#include <linux/init.h> +#include <linux/of.h> +#include <linux/of_device.h> +#include <linux/qda_compute_bus.h> +#include <linux/slab.h>
+static int qda_cb_bus_dma_configure(struct device *dev) +{
- return of_dma_configure(dev, dev->of_node, true);
+}
+const struct bus_type qda_cb_bus_type = {
- .name = "qda-compute-cb",
- .dma_configure = qda_cb_bus_dma_configure,
+}; +EXPORT_SYMBOL_GPL(qda_cb_bus_type);
+static void release_qda_cb_device(struct device *dev) +{
- of_node_put(dev->of_node);
- kfree(dev);
+}
+struct device *create_qda_cb_device(struct device *parent_device, const char *name,
u64 dma_mask, struct device_node *of_node)+{
- struct device *dev;
- int ret;
- dev = kzalloc_obj(*dev);
- if (!dev)
return ERR_PTR(-ENOMEM);- dev->release = release_qda_cb_device;
- dev->bus = &qda_cb_bus_type;
- dev->parent = parent_device;
- dev->coherent_dma_mask = dma_mask;
- dev->dma_mask = &dev->coherent_dma_mask;
- dev->of_node = of_node_get(of_node);
- dev_set_name(dev, "%s", name);
- ret = device_register(dev);
- if (ret) {
put_device(dev);return ERR_PTR(ret);- }
- return dev;
+} +EXPORT_SYMBOL_GPL(create_qda_cb_device);
+static int __init qda_cb_bus_init(void) +{
- int err;
- err = bus_register(&qda_cb_bus_type);
- if (err < 0) {
pr_err("qda-compute-cb bus registration failed: %d\n", err);return err;- }
- return 0;
+}
+postcore_initcall(qda_cb_bus_init); diff --git a/include/linux/qda_compute_bus.h b/include/linux/qda_compute_bus.h new file mode 100644 index 000000000000..90bf248c7285 --- /dev/null +++ b/include/linux/qda_compute_bus.h @@ -0,0 +1,32 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/*
- Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
- */
+#ifndef __QDA_COMPUTE_BUS_H__ +#define __QDA_COMPUTE_BUS_H__
+#include <linux/device.h>
+/*
- Custom bus type for QDA compute context bank (CB) devices
- This bus type is used for manually created CB devices that represent
- IOMMU context banks. The custom bus allows proper IOMMU configuration
- and device management for these virtual devices.
- */
+#ifdef CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS +extern const struct bus_type qda_cb_bus_type;
+struct device *create_qda_cb_device(struct device *parent_device, const char *name,
u64 dma_mask, struct device_node *of_node);+#else +static inline struct device *create_qda_cb_device(struct device *parent_device,
const char *name, u64 dma_mask,struct device_node *of_node)+{
- return ERR_PTR(-ENODEV);
+} +#endif
+#endif /* __QDA_COMPUTE_BUS_H__ */
-- 2.34.1