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

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Message-ID: <c0dee650-df1c-4fad-aa97-fb9eab03f3a2@arm.com>
Date:   Tue, 22 Feb 2022 21:30:30 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@...radead.org>,
        Mikko Perttunen <mperttunen@...dia.com>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com, joro@...tes.org,
        will@...nel.org, robh+dt@...nel.org, 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 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@...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.

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.