[linux-dvb] Re: More V4 Demux API Q's

[Rob.McConnell@Zarlink.Com]

                      Johannes                                                                                                   
                      Stezenbach               To:       linux-dvb@linuxtv.org                                                   
                      <js@convergence.d        cc:                                                                               
                      e>                       Subject:  [linux-dvb] Re: More V4 Demux API Q's                                   
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                      13-Jan-2004 05:02                                                                                          
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> Rob.McConnell@Zarlink.Com wrote:
> > Johannes Stezenbach wrote:
> > > I think usually there is one DMA buffer per section filter, whether
> > > they are on the same PID, same fd or not. (The av7110 driver uses
> > > software section filtering now, but usually one would use hardware
> > > section filters if they are available.) The common PID filter for
> > > multiple section filters on the same PID is handled within the
> > > driver and not visible in the API. The V3 implementation has
> > > a layer of additional buffers for the "kernel demux API" thing,
> > > but I try to get rid of that in V4. But if one would allow
> > > the output of multiple filters on the same fd, one would need an
> > > additional output ringbuffer, plus copying.
> >
> > OK, so the AV7110 functions differently to the h/w that I am familiar
with.
> > In fact, on this h/w there isn't one DMA buffer per section filter but
> > rather the output of all section filters attached to a single PID feed
get
> > DMAed to a single h/w buffer.  In this case, the s/w would have to do
the
> > additional work of separating the tables by their ID and copying the
data
> > to separate circular kernel buffers each associated with a process on a
> > different fd.  There is certainly more s/w overhead in the driver to
> > implement this, rather than allowing the complete section tables to be
> > allowed up to user space and the middleware to perform the filtering on
the
> > single fd.

> Hm, I checked the docs for some hw and it seems that you are damn right!
> Thanks for pointing this out.

> It seems that if we want to match the API up with the hw caps we need
> to have multiple section filters on one fd, but only if they are
> on the same PID. We would also have to disallow multiple filters
> for the same PID on different fds.

> But I know that this would be a pita for desktop Linux users, it's
> just too inconvenient if only one application can read PAT/PMT at
> the same time...

What is the current status for multiple section filters on a single fd?
Are you intending to support this, as there is a lot of h/w out there with
this requirement?

If we are to support it (which I strongly suggest we do), then we would
need the ability to ADD/DEL section filters to an fd (extra few ioctls).

Please let me know which direction we are going with this.

Thanks!

Rob : )




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