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

[Mauro Carvalho Chehab <mchehab-JPH+aEBZ4P+UEJcrhfAQsw@public.gmane.org>]

Em Thu, 08 Jan 2015 18:10:13 +0200
Laurent Pinchart <laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org> escreveu:

> 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.
> 

Ok, so let's stick with it for DVB. At DVB side, I don't see a need for
sub-sub-type, especially since DVB has no subdevs (except for the shared
tuner between DVB and V4L). Everything there are devnodes, with their
functionality strictly following the documentation, as the API is fully
handled inside the DVB core[1].

Also, I don't want to mix adding DVB media controller support with the
addition of a new ioctl.

[1] For the non-deprecated DVB devnodes. DVB have 3 devnode types that
are deprecated because they implement functionality found elsewhere
(video, audio and OSD dvb APIs). Only one legacy driver implements it,
and there's no plan to ever add media controller or expand/accept
new drivers using those legacy APIs.

Regards,
Mauro