[RFC PATCH 2/8] gpu: host1x: Add context bus

[Mikko Perttunen]

The context bus is a "dummy" bus that contains struct devices that
correspond to IOMMU contexts assigned through Host1x to processes.

Even when host1x itself is built as a module, the bus is registered
in built-in code so that the built-in ARM SMMU driver is able to
reference it.

Signed-off-by: Mikko Perttunen <mperttunen at nvidia.com>
---
 drivers/gpu/Makefile               |  3 +--
 drivers/gpu/host1x/Kconfig         |  5 +++++
 drivers/gpu/host1x/Makefile        |  1 +
 drivers/gpu/host1x/context_bus.c   | 31 ++++++++++++++++++++++++++++++
 include/linux/host1x_context_bus.h | 15 +++++++++++++++
 5 files changed, 53 insertions(+), 2 deletions(-)
 create mode 100644 drivers/gpu/host1x/context_bus.c
 create mode 100644 include/linux/host1x_context_bus.h

diff --git a/drivers/gpu/Makefile b/drivers/gpu/Makefile
index 835c88318cec..8997f0096545 100644
--- a/drivers/gpu/Makefile
+++ b/drivers/gpu/Makefile
@@ -2,7 +2,6 @@
 # drm/tegra depends on host1x, so if both drivers are built-in care must be
 # taken to initialize them in the correct order. Link order is the only way
 # to ensure this currently.
-obj-$(CONFIG_TEGRA_HOST1X)	+= host1x/
-obj-y			+= drm/ vga/
+obj-y			+= host1x/ drm/ vga/
 obj-$(CONFIG_IMX_IPUV3_CORE)	+= ipu-v3/
 obj-$(CONFIG_TRACE_GPU_MEM)		+= trace/
diff --git a/drivers/gpu/host1x/Kconfig b/drivers/gpu/host1x/Kconfig
index 6dab94adf25e..8546dde3acc8 100644
--- a/drivers/gpu/host1x/Kconfig
+++ b/drivers/gpu/host1x/Kconfig
@@ -1,7 +1,12 @@
 # SPDX-License-Identifier: GPL-2.0-only
+
+config TEGRA_HOST1X_CONTEXT_BUS
+	bool
+
 config TEGRA_HOST1X
 	tristate "NVIDIA Tegra host1x driver"
 	depends on ARCH_TEGRA || (ARM && COMPILE_TEST)
+	select TEGRA_HOST1X_CONTEXT_BUS
 	select IOMMU_IOVA
 	help
 	  Driver for the NVIDIA Tegra host1x hardware.
diff --git a/drivers/gpu/host1x/Makefile b/drivers/gpu/host1x/Makefile
index a48af2cefae1..d9fea2885658 100644
--- a/drivers/gpu/host1x/Makefile
+++ b/drivers/gpu/host1x/Makefile
@@ -19,3 +19,4 @@ host1x-y = \
 	hw/host1x07.o
 
 obj-$(CONFIG_TEGRA_HOST1X) += host1x.o
+obj-$(CONFIG_TEGRA_HOST1X_CONTEXT_BUS) += context_bus.o
diff --git a/drivers/gpu/host1x/context_bus.c b/drivers/gpu/host1x/context_bus.c
new file mode 100644
index 000000000000..2625914f3c7d
--- /dev/null
+++ b/drivers/gpu/host1x/context_bus.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2021, NVIDIA Corporation.
+ */
+
+#include <linux/device.h>
+#include <linux/of.h>
+
+struct bus_type host1x_context_device_bus_type = {
+	.name = "host1x-context",
+};
+EXPORT_SYMBOL(host1x_context_device_bus_type);
+
+static int __init host1x_context_device_bus_init(void)
+{
+	int err;
+
+	if (!of_machine_is_compatible("nvidia,tegra186") &&
+	    !of_machine_is_compatible("nvidia,tegra194") &&
+	    !of_machine_is_compatible("nvidia,tegra234"))
+		return 0;
+
+	err = bus_register(&host1x_context_device_bus_type);
+	if (err < 0) {
+		pr_err("bus type registration failed: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+postcore_initcall(host1x_context_device_bus_init);
diff --git a/include/linux/host1x_context_bus.h b/include/linux/host1x_context_bus.h
new file mode 100644
index 000000000000..72462737a6db
--- /dev/null
+++ b/include/linux/host1x_context_bus.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (c) 2021, NVIDIA Corporation. All rights reserved.
+ */
+
+#ifndef __LINUX_HOST1X_CONTEXT_BUS_H
+#define __LINUX_HOST1X_CONTEXT_BUS_H
+
+#include <linux/device.h>
+
+#ifdef CONFIG_TEGRA_HOST1X_CONTEXT_BUS
+extern struct bus_type host1x_context_device_bus_type;
+#endif
+
+#endif
-- 
2.30.0