Re: [PATCHv3 01/20] media: add new types for DVB devnodes

[Laurent Pinchart <laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>]

Hi Mauro,

On Wednesday 07 January 2015 12:22:39 Mauro Carvalho Chehab wrote:
> Em Wed, 07 Jan 2015 16:09:04 +0200 Sakari Ailus escreveu:
> > Mauro Carvalho Chehab wrote:
> > > Most of the DVB subdevs have already their own devnode.
> > > 
> > > Add support for them at the media controller API.
> > > 
> > > Signed-off-by: Mauro Carvalho Chehab <mchehab-JPH+aEBZ4P+UEJcrhfAQsw@public.gmane.org>
> > > 
> > > diff --git a/include/uapi/linux/media.h b/include/uapi/linux/media.h
> > > index 7902e800f019..707db275f92b 100644
> > > --- a/include/uapi/linux/media.h
> > > +++ b/include/uapi/linux/media.h
> > > @@ -50,7 +50,14 @@ struct media_device_info {
> > > 
> > >   #define MEDIA_ENT_T_DEVNODE_V4L		(MEDIA_ENT_T_DEVNODE + 1)
> > >   #define MEDIA_ENT_T_DEVNODE_FB		(MEDIA_ENT_T_DEVNODE + 2)
> > >   #define MEDIA_ENT_T_DEVNODE_ALSA	(MEDIA_ENT_T_DEVNODE + 3)
> > > 
> > > -#define MEDIA_ENT_T_DEVNODE_DVB		(MEDIA_ENT_T_DEVNODE + 4)
> > > +#define MEDIA_ENT_T_DEVNODE_DVB_FE	(MEDIA_ENT_T_DEVNODE + 4)
> > > +#define MEDIA_ENT_T_DEVNODE_DVB_DEMUX	(MEDIA_ENT_T_DEVNODE + 5)
> > > +#define MEDIA_ENT_T_DEVNODE_DVB_DVR	(MEDIA_ENT_T_DEVNODE + 6)
> > > +#define MEDIA_ENT_T_DEVNODE_DVB_CA	(MEDIA_ENT_T_DEVNODE + 7)
> > > +#define MEDIA_ENT_T_DEVNODE_DVB_NET	(MEDIA_ENT_T_DEVNODE + 8)
> > 
> > I'd create another type for the DVB sub-type devices, as there is for
> > V4L2 sub-devices. I wonder what Laurent thinks.
> 
> I discussed this quickly with Laurent on IRC.
> 
> There are some concept differences between V4L2 and DVB.
> 
> At v4l2:
> - the spec is one monolitic header (videodev2.h);
> - one devnode is used to control everyhing (/dev/video?)
> - there is one v4l core for all types of devices
> 
> At DVB:
> - each different DVB API has its own header;
> - each DVB device type has its own core (ok, they're
>   linked into one module, but internally they're almost independent);
> - each different DVB API has its own devnode.
> 
> So, using "SUBDEV" for DVB (or at least for the devnodes) don't
> make much sense.
> 
> Ok, there are still some things at DVB side that could be mapped as
> subdev. The clear example is the tuner. However, in this case, the
> same tuner can be either V4L, DVB or both. So, we need to define just
> one subdev type for the tuner.
> 
> Also, each DVB device can be identified via major/minor pairs.
> 
> I wrote already (and submitted upstream) the patches for media-ctl to
> recognize them. They're also on my experimental v4l-utils tree:
> 	http://git.linuxtv.org/cgit.cgi/mchehab/experimental-v4l-> 	utils.git/log/?h=dvb-media-ctl

As I've mentioned in a previous discussion, the media_entity type field is too 
restrictive. Not only does this use case show that we need a type, sub-type 
and sub-sub-type, there are also entities that implement several distinct 
types. I thus believe we need a new ioctl is needed to expose detailed 
information about entities. This topic has been discussed numerous times in 
the past, it "just" requires someone to implement it.

I'm not opposed to a short-term solution like the one proposed here, but maybe 
we should instead decide it's time to implement the new ioctl instead.

-- 
Regards,

Laurent Pinchart