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

[Vishnu Reddy]

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@xxxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxxx>
> > ---
> >   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