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

[Laurent Pinchart]

On Mon, Mar 30, 2026 at 09:55:23PM +0300, Dmitry Baryshkov wrote:
> On Mon, Mar 30, 2026 at 03:11:58PM +0100, Bryan O'Donoghue wrote:
> > On 30/03/2026 14:46, johannes.goede@xxxxxxxxxxxxxxxx wrote:
> > > > > And then your CCMv1 or CCMv2 helper will get called with
> > > > > the matching parameter-data.
> > > >
> > > > This leads to userspace having to know exact format for each hardware
> > > > version, which is not nice. At the very least it should be possible to
> > > > accept CCMv1 buffers and covert them to CCMv2 when required.
> > >
> > > Yes, but a new ISP may also have a different pipeline altogether
> > > with e.g. more then one preview/viewfinder output vs one viewfinder
> > > output for current hw, etc.
> > 
> > My scoping on HFI shows that the IQ structures between Kona and later
> > versions have pretty stable data-structures.
> > 
> > It might be worthwhile for the non-HFI version to implement those
> > structures.
> > 
> > I keep mentioning CDM. Its also possible to construct the buffer in the
> > format the CDM would require and hand that from user-space into the kernel.
> > 
> > That would save alot of overhead translating from one format to another.
> > 
> > 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.
> > 
> > TBH I think the CDM should happen for this system and in that vein is there
> > any reason not to pack the data in the order the CDM will want ?
> 
> This sounds like the most horrible idea: letting userspace directly
> program any registers in a way that is not visible to the kernel.

ISP hardware is typically not designed to make this safe, so I would be
really, really careful about going in that direction. It also seems a
dangerous idea to me.

> > So probably in fact IQ structs are not the right thing for OPE+IFE.

-- 
Regards,

Laurent Pinchart