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

[Vishnu Reddy <busanna.reddy@oss.qualcomm.com>]

On 4/14/2026 10:19 PM, Greg Kroah-Hartman wrote:
> On Tue, Apr 14, 2026 at 10:01:15PM +0530, 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 +++++++++++++++
>>   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
> 
> So this is a context-free bus?  I.e. no documentation?
> 
> :)
> 
> This feels really odd, this "bus" isn't doing anything at all.  So why
> do you need it and can't use auxbus or faux?

Looks like the device have specific iommu configuration (via 
of_dma_configure()), then using the auxbus or faux bus types does not 
have the bus notifier calls to iommu_release_device(). Please correct me 
if I misunderstood?

> 
> You say something about an iommu, but yet this has no information about
> an iommu at all, so why are they somehow special?
> 
> You need to provide a lot more information here, sorry.
> 
> greg k-h
> 
>