Re: [PATCH RFC 04/18] accel/qda: Add built-in compute CB bus for QDA and integrate with IOMMU

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Wed, Feb 25, 2026 at 11:26:52PM +0530, Ekansh Gupta wrote:
> 
> 
> On 2/24/2026 4:14 AM, Dmitry Baryshkov wrote:
> > On Tue, Feb 24, 2026 at 12:38:58AM +0530, Ekansh Gupta wrote:
> >> Introduce a built-in compute context-bank (CB) bus used by the Qualcomm
> >> DSP accelerator (QDA) driver to represent DSP CB devices that require
> >> IOMMU configuration. This separates the CB bus from the QDA driver and
> >> allows QDA to remain a loadable module while the bus is always built-in.
> > Why? What is the actual problem that you are trying to solve?
> Bus needs to be built-in as it is being used by iommu driver. I'll add more details here.

It's an implementation detail. Start your commit message with the
description of the issue or a problem that you are solving.

> >
> >> A new bool Kconfig symbol DRM_ACCEL_QDA_COMPUTE_BUS is added and is
> > Don't describe the patch contents. Please.
> Ack.
> >
> >> selected by the main DRM_ACCEL_QDA driver. The parent accel Makefile is
> >> updated to descend into the QDA directory for both built-in and module
> >> builds so that the CB bus is compiled into vmlinux while the driver
> >> remains modular.
> >>
> >> The CB bus is registered at postcore_initcall() time and is exposed to
> >> the IOMMU core through iommu_buses[] in the same way as the Tegra
> >> host1x context-bus. This enables later patches to create CB devices on
> >> this bus and obtain IOMMU domains for them.
> > Note, there is nothing QDA-specific in this patch. Please explain, why
> > the bus is QDA-specific? Can we generalize it?
> I needed a custom bus here to use for the compute cb devices for iommu
> configurations, I don't see any reason to keep it QDA-specific. The only requirement
> is that this should be enabled built in whenever QDA is enabled.

Why? FastRPC uses platform_bus. You need to explain, why it's not
correct.

> 
> But if I keep it generic, where should this be placed? Should it be accel(or drm?) specific?

drivers/base? Or drivers/iommu? That would totally depend on the issue
description. E.g. can we use the same code for host1x?


-- 
With best wishes
Dmitry