Re: [PATCH v3 2/9] gpu: host1x: Add context bus

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On 2022-02-22 16:21, Christoph Hellwig wrote:
On Fri, Feb 18, 2022 at 01:39:45PM +0200, Mikko Perttunen wrote:
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@xxxxxxxxxx>
---
  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-$(CONFIG_TRACE_GPU_MEM)		+= trace/
diff --git a/drivers/gpu/host1x/Kconfig b/drivers/gpu/host1x/Kconfig
index 6815b4db17c1..1861a8180d3f 100644
--- a/drivers/gpu/host1x/Kconfig
+++ b/drivers/gpu/host1x/Kconfig
@@ -1,8 +1,13 @@
  # SPDX-License-Identifier: GPL-2.0-only
+
+config TEGRA_HOST1X_CONTEXT_BUS
+	bool
+
  config TEGRA_HOST1X
  	tristate "NVIDIA Tegra host1x driver"
  	depends on ARCH_TEGRA || (ARM && COMPILE_TEST)
  	select DMA_SHARED_BUFFER
+	select TEGRA_HOST1X_CONTEXT_BUS
  	select IOMMU_IOVA
  	help
  	  Driver for the NVIDIA Tegra host1x hardware.
diff --git a/drivers/gpu/host1x/Makefile b/drivers/gpu/host1x/Makefile
index d2b6f7de0498..c891a3e33844 100644
--- a/drivers/gpu/host1x/Makefile
+++ b/drivers/gpu/host1x/Makefile
@@ -18,3 +18,4 @@ host1x-y = \
  	hw/host1x07.o
obj-$(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);

EXPORT_SYMBOL_GPL, please.

But the pattern that this copies in arm_smmu_bus_init is really
ugly.  I think we need to figure out a way todo that without having
to export all the low-level bus types.

Yup, as it happens that was the first step on my mission :)

https://gitlab.arm.com/linux-arm/linux-rm/-/commits/iommu/bus

Still a way to go with the main meat of that work, though, so I was figuring this could probably land as-is and I'll sweep it up in due course.

Robin.



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