[PATCH 04/15] accel/qda: Add compute bus for QDA context banks
From: Ekansh Gupta via B4 Relay
Date: Tue May 19 2026 - 02:22:44 EST
From: Ekansh Gupta <ekansh.gupta@xxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxx>
---
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-$(CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS) += qda/
obj-$(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