[pvrusb2] speedup mythtv frequency changes

[Mike Isely]

On Fri, 6 Jan 2006, Ingo Flaschberger wrote:

> Hi Mike,
>
> I want to speed up frequency changes with mythtv.
> Mythtv have the not really nice habit to always set Contrast, Saturation, 
> Brightness and Hue.
>
> It should be possible from the pvrusb2 driver only to update the i2c chips 
> when really anything has changed and will speed up the changes.
>
> As far as I have seen pvr2_hdw_commit_ctl in pvrusb2-hdw.c would be a good 
> place to implement this?
> Could pvr2_hdw_commit_ctl called with more than one thing to change??
>
> Need some tips where to implement this.

It already does that.

Every "control" in the pvrusb2 driver has a dirty flag associated with it; 
the commit function will then handle updating of everything that is dirty 
at that point.  What happens is roughly like this:

1. Application changes one or more controls, causing corresponding dirty 
flags to be set.

2. The commit function is called internally by the driver to commit all 
dirty state.  It (as of the 20051231 snapshot) does three things to 
accomplish this:

2a. The commit function handles some side effects, e.g. adjusting a 
control if a related control becomes dirty - that generally only applies 
to changing of the video standard or frequency vs channel table stuff.

2b. The commit function will toggle subsystems in the driver which must be 
impacted by the dirty state.  For example, if the capture resolution gets 
changed, then it will cause streaming to restart if it was in progress.

2c. (Changed for 20051231) The module controlling logic will be given a 
chance to notice dirty controls and trigger updates to corresponding 
modules.  Before 20051231, this was all done more directly within the 
commit function; now that level of control is moved out to logic which is 
closer to the I2C side (however the result is the same).

The running theme here is that updates are only sent for things that have 
changed and for what makes sense given the change.  The driver already 
won't gratuitously update things that don't make sense, and it won't reset 
streaming as a side effect unless it knows that it has to (and for bcsh 
adjustments streaming should be unaffected).

   -Mike

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