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

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Date:   Tue, 22 Feb 2022 08:21:28 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Mikko Perttunen <mperttunen@...dia.com>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com, joro@...tes.org,
        will@...nel.org, robh+dt@...nel.org, robin.murphy@....com,
        linux-tegra@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 2/9] gpu: host1x: Add context bus

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@...dia.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-$(CONFIG_TRACE_GPU_MEM)		+= trace/
> diff --git a/drivers/gpu/host1x/Kconfig b/drivers/gpu/host1x/Kconfig
> index 6815b4db17c1..1861a8180d3f 100644
> --- a/drivers/gpu/host1x/Kconfig
> +++ b/drivers/gpu/host1x/Kconfig
> @@ -1,8 +1,13 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> +
> +config TEGRA_HOST1X_CONTEXT_BUS
> +	bool
> +
>  config TEGRA_HOST1X
>  	tristate "NVIDIA Tegra host1x driver"
>  	depends on ARCH_TEGRA || (ARM && COMPILE_TEST)
>  	select DMA_SHARED_BUFFER
> +	select TEGRA_HOST1X_CONTEXT_BUS
>  	select IOMMU_IOVA
>  	help
>  	  Driver for the NVIDIA Tegra host1x hardware.
> diff --git a/drivers/gpu/host1x/Makefile b/drivers/gpu/host1x/Makefile
> index d2b6f7de0498..c891a3e33844 100644
> --- a/drivers/gpu/host1x/Makefile
> +++ b/drivers/gpu/host1x/Makefile
> @@ -18,3 +18,4 @@ host1x-y = \
>  	hw/host1x07.o
>  
>  obj-$(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.