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

[Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>]

On 2/26/2026 12:39 AM, Dmitry Baryshkov wrote:
> 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.
Ack.
>
>>>> 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.
Ack.
>
>> 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?
I'll evaluate and bring this change separately for fastrpc and host1x.
>
>