Re: [RFC PATCH 2/3] media: qcom: camss: Add CAMSS Offline Processing Engine driver

[Bryan O'Donoghue <bod@kernel.org>]

On 05/04/2026 21:11, Laurent Pinchart wrote:
> The mali-c55 driver does this, it translates the ISP parameters buffers
> to a list of register values in userspace context, when the buffer is
> queued. In the IRQ handler, it then either copies those values to
> registers with MMIO writes, or use a DMA engine, depending on the
> platform. The rppx1 driver does something similar, with a different
> format for the buffer containing the register values.
> 
> I think this architecture could be replicated here. This translation in
> userspace context ensures that work at IRQ time is limited. The driver
> can use whatever DMA engine is available depending on the platform, and
> we can also force usage of MMIO for debugging or development purpose.
> That way, development of ISP features is decoupled from development of
> CDM support, enabling parallel development if desired, and faster
> plaform enablement that allows starting the userspace side of the work
> quicker.

I think that's a reasonable plan.

We make the buffer in user-space which could be used by CDM but stage 
the implementation.

That way if CDM proves too hard, we can do MMIO for a while, and then 
transition to CDM if/when.

For me though I really think translating between formats is storing up pain.

---
bod