[PATCH RFC 04/18] accel/qda: Add built-in compute CB bus for QDA and integrate with IOMMU

[Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>]

Introduce a built-in compute context-bank (CB) bus used by the Qualcomm
DSP accelerator (QDA) driver to represent DSP CB devices that require
IOMMU configuration. This separates the CB bus from the QDA driver and
allows QDA to remain a loadable module while the bus is always built-in.

A new bool Kconfig symbol DRM_ACCEL_QDA_COMPUTE_BUS is added and is
selected by the main DRM_ACCEL_QDA driver. The parent accel Makefile is
updated to descend into the QDA directory for both built-in and module
builds so that the CB bus is compiled into vmlinux while the driver
remains modular.

The CB bus is registered at postcore_initcall() time and is exposed to
the IOMMU core through iommu_buses[] in the same way as the Tegra
host1x context-bus. This enables later patches to create CB devices on
this bus and obtain IOMMU domains for them.

Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
---
 drivers/accel/Makefile              |  1 +
 drivers/accel/qda/Kconfig           |  5 +++++
 drivers/accel/qda/Makefile          |  2 ++
 drivers/accel/qda/qda_compute_bus.c | 23 +++++++++++++++++++++++
 drivers/iommu/iommu.c               |  4 ++++
 include/linux/qda_compute_bus.h     | 22 ++++++++++++++++++++++
 6 files changed, 57 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..ef1fa384efbe 100644
--- a/drivers/accel/qda/Kconfig
+++ b/drivers/accel/qda/Kconfig
@@ -3,11 +3,16 @@
 # 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 e7f23182589b..242684ef1af7 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..1d9c39948fb5
--- /dev/null
+++ b/drivers/accel/qda/qda_compute_bus.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+#include <linux/device.h>
+#include <linux/init.h>
+
+struct bus_type qda_cb_bus_type = {
+	.name = "qda-compute-cb",
+};
+EXPORT_SYMBOL_GPL(qda_cb_bus_type);
+
+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/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 4926a43118e6..5dee912686ee 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -33,6 +33,7 @@
 #include <trace/events/iommu.h>
 #include <linux/sched/mm.h>
 #include <linux/msi.h>
+#include <linux/qda_compute_bus.h>
 #include <uapi/linux/iommufd.h>
 
 #include "dma-iommu.h"
@@ -178,6 +179,9 @@ static const struct bus_type * const iommu_buses[] = {
 #ifdef CONFIG_CDX_BUS
 	&cdx_bus_type,
 #endif
+#ifdef CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS
+	&qda_cb_bus_type,
+#endif
 };
 
 /*
diff --git a/include/linux/qda_compute_bus.h b/include/linux/qda_compute_bus.h
new file mode 100644
index 000000000000..807122d84e3f
--- /dev/null
+++ b/include/linux/qda_compute_bus.h
@@ -0,0 +1,22 @@
+/* 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 struct bus_type qda_cb_bus_type;
+#endif
+
+#endif /* __QDA_COMPUTE_BUS_H__ */

-- 
2.34.1