Re: [PATCH 1/3] drivers: base: Add generic context device bus

[Srinivas Kandagatla <srini@kernel.org>]

On 4/14/26 4:31 PM, Ekansh Gupta via B4 Relay wrote:
> From: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> 
> Introduce a new generic bus type for synthetic context bank devices
> that require IOMMU context isolation. This bus provides a shared
> infrastructure for accelerator and GPU drivers that create virtual
> devices representing IOMMU context banks.
> 
> Currently, drivers like host1x implement their own bus types for
> context devices. This generic implementation allows multiple drivers
> to share the same bus infrastructure, simplifying the IOMMU subsystem
> integration and reducing code duplication.
> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/base/Kconfig        |  3 +++
>  drivers/base/Makefile       |  1 +
>  drivers/base/context_bus.c  | 24 ++++++++++++++++++++++++
>  include/linux/context_bus.h | 15 +++++++++++++++

This patch as it is does not add any details on how the iommu will be
binded to this bus, Please consider adding the iommu changes to this
patch so that its easy to understand and for completeness.


Also naming it as context bus is bit generic, I think the whole purpose
of this is bus is to add this as another supported bus in the iommu.

may be iommu_context bus or something on those lines would be much clear.


>  4 files changed, 43 insertions(+)
> 
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index f7d385cbd3ba..479bc4bb442b 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -4,6 +4,9 @@ menu "Generic Driver Options"
>  config AUXILIARY_BUS
>  	bool
>  
> +config CONTEXT_DEVICE_BUS
> +	bool
> +
>  config UEVENT_HELPER
>  	bool "Support for uevent helper"
>  	help
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 8074a10183dc..ab9a0b2dc73b 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -8,6 +8,7 @@ obj-y			:= component.o core.o bus.o dd.o syscore.o \
>  			   topology.o container.o property.o cacheinfo.o \
>  			   swnode.o faux.o
>  obj-$(CONFIG_AUXILIARY_BUS) += auxiliary.o
> +obj-$(CONFIG_CONTEXT_DEVICE_BUS) += context_bus.o
>  obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
>  obj-y			+= power/
>  obj-$(CONFIG_ISA_BUS_API)	+= isa.o
> diff --git a/drivers/base/context_bus.c b/drivers/base/context_bus.c
> new file mode 100644
> index 000000000000..6ddb6c27bf69
> --- /dev/null
> +++ b/drivers/base/context_bus.c
> @@ -0,0 +1,24 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +// Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.

Some credits to the inspiring code would be nice.

> +
> +#include <linux/context_bus.h>
> +#include <linux/init.h>
> +
> +const struct bus_type context_device_bus_type = {
> +	.name = "context-device",
> +};
> +EXPORT_SYMBOL_GPL(context_device_bus_type);
> +
> +static int __init context_device_bus_init(void)
> +{
> +	int err;
> +
> +	err = bus_register(&context_device_bus_type);
> +	if (err < 0) {
> +		pr_err("context-device bus registration failed: %d\n", err);
> +		return err;
> +	}
> +
> +	return 0;
> +}

So is the consumer drivers are expected to do the device management for
this bus, this certainly is not correct and every consumer would be
duplicating it.

Did you consider faux bus?

> +postcore_initcall(context_device_bus_init);
> diff --git a/include/linux/context_bus.h b/include/linux/context_bus.h
> new file mode 100644
> index 000000000000..0cd44cb5b147
> --- /dev/null
> +++ b/include/linux/context_bus.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + */
> +
> +#ifndef __LINUX_CONTEXT_BUS_H
> +#define __LINUX_CONTEXT_BUS_H
> +
> +#include <linux/device.h>
> +
> +#ifdef CONFIG_CONTEXT_DEVICE_BUS
> +extern const struct bus_type context_device_bus_type;
> +#endif
> +
> +#endif /* __LINUX_CONTEXT_BUS_H */
>