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

Philip Prindeville philipp_subx at redfish-solutions.com
Thu Nov 3 07:48:41 CET 2005

Michael Krufky wrote:

> Edgar Toernig wrote:
>> Philip Prindeville wrote:
>>> Hmmm...   I personally have little use for the video functionality
>>> that a lot of DVB cards come with...
>>> Who actually uses the video capture logic?
>> I do.  In fact, I've bought the card only because it has an additional
>> (S-)Video-In connector for my game console (or vhs-recorder).
>>> I've always wondered...   On a multi-function card, does the driver
>>> have to handle all aspects of that functionality?  Or can you have
>>> separate, stand-alone drivers that each handle one type of
>>> functionality, without them having to be aware of each other
>>> or interact with each other?
>> 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.
>> It should be possible to create a dummy bttv driver that only
>> supplies GPIO and I2C access.  This dummy driver could even be
>> part of the dvb-bt878 driver.  (I may be wrong but wasn't the
>> first version of the dvb-bt878 driver like that?)  But you
>> have to find someone who's willing spends some hours of work
>> to do that :-)  I wouldn't - it's unsatisfying to invest a
>> lot of work just to "remove" functionality.
> Sure it's possible, but please, don't.  This would be moving 
> backwards.  Why write out a driver that isnt going to go away?
> It's ONE kernel.  One kernel, with subsystems, that are all part of 
> the same ONE KERNEL.
> -Mike

Which has the undesirable effect of causing changes to have a ripple effect
all through the code, rather than being neatly self-contained.  Too bad
that V4L doesn't evolve independently of DVB.



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