[mythtv] Merging cards and inputs, testing help needed

[David Engel]

On Tue, Jan 20, 2015 at 05:15:14PM -0500, Devin Heitmueller wrote:
> This is definitely interesting work.  A couple of questions, related
> to hybrid cards (i.e. card which have both a DVB and V4L2 input which
> cannot be used at the same time).
> 
> 1.  How do you know a V4L2 device and a DVB device are part of the
> same hybrid card?  Do you have some heuristic that you have written
> which tells you the device nodes are from the same card?  (I'm asking
> because I may be able to help in this area)
> 2.  How are you replacing the construct for what today are known as
> "input groups"?  Today input groups are used to prevent the DVB and
> V4L2 device from being used simultaneously.  Presumably you'll need to
> provide some similar capability to either indicate within a card that
> certain inputs cannot be used simultaneously, or be able to detect
> this condition programatically.
> 
> If you've already thought through these cases and have a solution, I'm
> happy to offer some input (my involvement with the LinuxTV project as
> well as having worked for a manufacturer of such tuners suggests I'm
> well-versed in such issues).  If you haven't yet considered these
> cases, I'm happy to talk through them a bit and explain some of the
> challenges and why it may be more complicated than it looks.

Hi Devin,

Input groups (or card groups or whatever we call them) aren't going
away.  They will still be used to tie together the virtual tuners for
the same physical card.  They will also be used to tie together the
"separate cards"(*) in the, probably rare, cases where multiple inputs
on the same card are used.

(*)Previously, a setup using multiple inputs could have looked like
this:

   Card 1: /dev/video0 =======> Input 1: Television
                       |======> Input 2: Composite
		       \======> Input 3: S-Video

Now, it would look like this:

   Card 1: /dev/video0, Television input
   Card 2: /dev/video0, Composite input
   Card 3: /dev/video0, S-Video input

Also, in this case, the user won't have to do anything special to
configure the required input groups.  MythTV will see that they all
use /dev/video0 and create the group automatically.

Hybrid cards like the HVR-2250 will still be problematic.  I suppose
it might be possible to scan /sys to see if a V4L entry and a DVB
entry both lead to the same PCI(e) device, but that's not something I
was planning on doing.  When the user wants to use both the V4L and
DVB parts of a card in such cases, they'll still have to manually
configure the necessary input groups.

David
-- 
David Engel
david at istwok.net