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

[Dmitry Baryshkov]

On Mon, Mar 30, 2026 at 03:32:55PM +0100, Bryan O'Donoghue wrote:
> On 30/03/2026 15:27, johannes.goede@xxxxxxxxxxxxxxxx wrote:
> > > That's another reason I bring up CDM again and again. We probably don't want to fix to the wrong format for OPE, introduce the CDM and then find we have to map from one format to another for large and complex data over and over again for each frame or every N frames.
> > CDM is a much lower-level API then what is expected from
> > a media-controller centric V4L2 driver. Basically the OPE
> > driver will export:
> 
> My concern is about wrappering one thing inside of another thing and then
> stuffing it again back into CDM and doing the same on the way out.
> 
> There are already 50 MMIO writes in the OPE ISR, I don't believe it is
> sustainable to keep adding MMIO into that.

That's why I asked about the ABI. If we have a format for OPE
programming, we can reuse it for CDM. If we don't, we have to open the
wormhole. That is unless we make OPE driver utilize CDM instead of
writing registers through MMIO (and instead of userspace directly
programming the CDM).

> 
> I'm aware of a project in qcom that did something with making the CDM format
> in libcamera and handed that off to kernel, recommend looking into that.
> 
> ---
> bod

-- 
With best wishes
Dmitry