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Re: DVB ioctl FE_GET_EVENT behaviour broken in 3.3

On 06.04.2012 13:49, Chris Rankin wrote:
The reason that DVB playback with xine is broken in 3.3 is that the
userspace semantics of FE_GET_EVENT have changed. Xine tunes into a DVB
channel as follows:

* discards stale frontend events by calling FE_GET_EVENT until there is
none left.
* calls FE_SET_FRONTEND with the new frequency.
* starts polling for new frontend events by calling FE_GET_EVENT again.

Xine assumes that *every* FE_GET_EVENT after calling FE_SET_FRONTEND
will have dvb_frontend_event.parameters.frequency set to the new
frequency, if this channel exists. However, under Linux 3.3, at least
the first new event with a newly-plugged-in device has a frequency
parameter of zero. I am assuming that Linux is populating the frequency
parameter from an internal data structure because xine behaves normally
once some other DVB application manages to set it to something other
than zero. And xine then continues to behave normally until I unplug the
DVB adapter and plug in back in again.

So the question is: why is there no frequency for this first
FE_GET_EVENT? Are the parameters incomplete, or shouldn't this event
have been sent in the first place?

I have no enough experience, but IMHO all frontend parameters should be available just after demod is LOCKed. Before LOCK you cannot know many parameters at all and frequency also can be changed a little bit during tuning process (ZigZag tuning algo).

Could you try to git bisect to find out patch causing that regression?

I suspect it is some change done for DVB core, git log drivers/media/dvb/dvb-core/ shows rather many patches that could be the reason.

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