[libcamera-devel] [PATCH v2 2/2] pipeline: raspberrypi: Allow registration of multiple cameras

[Laurent Pinchart]

Hi Sakari,

On Tue, Nov 23, 2021 at 06:28:56PM +0200, Sakari Ailus wrote:
> Hi Laurent, Naushir,
> 
> On Mon, Nov 22, 2021 at 03:00:40PM +0200, Laurent Pinchart wrote:
> > > -bool PipelineHandlerRPi::registerCameras()
> > > +int PipelineHandlerRPi::registerCameras(MediaDevice *unicam, MediaDevice *isp,
> > > +					const std::string &deviceId)
> > >  {
> > >  	std::unique_ptr<RPiCameraData> data = std::make_unique<RPiCameraData>(this);
> > > +
> > >  	if (!data->dmaHeap_.isValid())
> > > -		return false;
> > > +		return -ENOMEM;
> > > +
> > > +	MediaEntity *unicamImage = unicam->getEntityByName("unicam" + deviceId + "-image");
> > > +	MediaEntity *ispOutput0 = isp->getEntityByName("bcm2835-isp" + deviceId + "-output0");
> > > +	MediaEntity *ispCapture1 = isp->getEntityByName("bcm2835-isp" + deviceId + "-capture1");
> > > +	MediaEntity *ispCapture2 = isp->getEntityByName("bcm2835-isp" + deviceId + "-capture2");
> > > +	MediaEntity *ispCapture3 = isp->getEntityByName("bcm2835-isp" + deviceId + "-capture3");
> > 
> > I'm wondering if wildcards would be nice here too, but maybe a simpler
> > option would be to not include the device ID in the entity names in the
> > driver ? We have a bus info field that the kernel reports for the media
> > device, to differentiate between multiple instances of the same device.
> > I suppose we are missing guidelines on the kernel side regarding entity
> > naming. Sakari, any opinion on this ?
> 
> I think it'd be best to be able to match multiple fields, not just entity
> name. But I guess a regex goes a long way already.
> 
> There are some (unwritten?) rules for naming devices and they mostly work.

This is the part I'd like your opinion on. I can read written rules
myself, but have harder access to the ones that are only in your brain
:-)

>From an MC point of view, my understanding is that the driver and model
names should not be instance-specific (the model can vary between
different SoCs that integrate different versions/models of the same IP,
but shouldn't differ between multiple instances of the same IP in a
given SoC, at least if those instances are identical). For entity names,
we have a (probably unwritten) requirement for all entities in a given
media device to have different names. What's your opinion about entity
names when we have different media devices that correspond to multiple
instances of the same IP core ? For instance, with two completely
independent CSI-2 receivers, exposed as two separate media graphs, would
you name the CSI-2 RX subdevs differently or identically ? If named
differently, how would they differ ?

> What's deviceId here? Would you need that as these are on separate MC
> devices? (I suppose it's up to the driver thought.)

In this specific case it's an index (equal to 0 or 1) that identifies a
particular instance of the ISP (there's a single ISP at the hardware
level, exposed as two virtual instances by the firmware).

-- 
Regards,

Laurent Pinchart