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Re: [RFC] [media] cx231xx: restore tuner settings on first open



On Mon, 2012-06-18 at 09:29 +0200, Hans Verkuil wrote:
> On Mon June 18 2012 06:49:58 David Dillow wrote:
> > What does the V4L2 API spec say about tuning frequency being persistent
> > when there are no users of a video capture device? Is MythTV wrong to
> > have that assumption, or is cx231xx wrong to not restore the frequency
> > when a user first opens the device?
> 
> Tuner standards and frequencies must be persistent. So cx231xx is wrong.
> Actually, all V4L2 settings must in general be persistent (there are
> some per-filehandle settings when dealing with low-level subdev setups or
> mem2mem devices).

Is there a document somewhere I can reference; I need to go through the
cx231xx driver and make sure it is doing the right things and it would
be handy to have a checklist.

> > Either way, I think MythTV should keep the device open until it is done
> > with it, as that would avoid added latency from putting the tuner to
> > sleep and waking it back up. But, I think we should address the issue in
> > the driver if it is not living up to the guarantees of the API.
> 
> From what I can tell it is a bug in the tda tuner (not restoring the frequency)
> and cx231xx (not setting the initial standard and possibly frequency).

Ok, I'll break this up and have a go at a proper fix. Thanks for the
pointers on the persistence of parameters.

Dave

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