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

[Robin Murphy]

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.