[RFC] Hybrid cards was Re: [linux-dvb] Re: backwards compatability -was- actual cvs broken?

Hartmut Hackmann hartmut.hackmann at t-online.de
Thu Nov 3 22:43:54 CET 2005

Hi, all

I don't know how bt878 handles the transport stream, maybe it does some
funny thing similar to the saa7146. But speaking from saa713x point of
view, there is only little conflict:
The chips have a separate transport stream interface and the interface
occupies a rarely used DMA channel. The chips can stream analog video,
sound and dvb parallel, only the planar mode is impossible.
Most of the cards available are hybrid ones, they can do analog and dvb.
Many share a single tuner. this of corse causes a conflict. But besides
this even parallel analog and dvb works in linux.
So - where do these cards belog?
I think we should leave things as they are. Most of the driver code is
initializing and handling of the PCI bridge, setting up and handling
the DMA, I2c etc. This would be needed in both, v4l and dvb and at least
be very similar. But even if we had it duplicated, handling hybrid cards
would be extremely difficult because we can have the PCI code only
once in this case.
But this can be different for bt8xx and cx88.

Best regards

Manu Abraham wrote:
> Edgar Toernig wrote:
>> Speaking about the BT878 based cards, the connection is already
>> pretty loose.  The BT878 has two functional blocks - video capture
>> and audio capture which show up as two different PCI devices.
>> The bttv driver handles the video capture part and works fine
>> without the dvb-driver.  The DVB "receiver" is connected to the
>> audio part.  Unfortunately, the DVB receiver usually needs the I2C
>> bus and some GPIO pins which are both part of the "video"-function
>> of the BT878.  So the DVB driver has to contact the bttv driver
>> whenever it wants access to these pins.
> There can be even more complicated issues. Imagine the bttv(878) is 
> connected to an ASIC. This ASIC controls both Analog and Digital.
> but the pronounced operations are all DVB. The analog operations are 
> quite minimal. something like mute audio etc. Now it would look like the 
> DVB parts is now handling the analog part too. For example how would 
> this mute_audio be called, since there is no mute audio under DVB..
> So where should this module belong ?
> If someone comments on this, i would be interested in havinging a 
> feedback on this. At present i have a few cards that have DVB-T + CVBS 
> on the dst, as well ATSC + NTSC.

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