[PATCH 2/2 v2] dma: ipu_idmac: do not lose valid received data in the irq handler

[Guennadi Liakhovetski]

On Mon, 7 Feb 2011, Anatolij Gustschin wrote:

> On Mon, 7 Feb 2011 12:35:44 +0100 (CET)
> Guennadi Liakhovetski <g.liakhovetski at gmx.de> wrote:
> 
> > On Mon, 7 Feb 2011, Anatolij Gustschin wrote:
> > 
> > > On Mon, 7 Feb 2011 12:09:15 +0100 (CET)
> > > Guennadi Liakhovetski <g.liakhovetski at gmx.de> wrote:
> > > ...
> > > > > I can't try mplayer since I don't have mplayer setup for this.
> > > > > But looking at the mplayer source I don't see why it should
> > > > > behave differently. Depending on mode mplayer queues 2 or 6
> > > > > buffers. Testing with my test app with 6 queued buffers shows
> > > > > no issues, here the buffer numbers toggle correctly, too.
> > > > 
> > > > Ok, I've done a couple more tests. With larger frames, and, therefore 
> > > > lower fps - yes, with your patch buffers toggle correctly. Whereas in my 
> > > > tests with smaller frames and higher fps either only one buffer is used, 
> > > > or one is used much more often, than the other, e.g., 0 0 0 1 0 0 0 1 0... 
> > > > Could you try to verify? Without your patch with any fps buffers toggle 
> > > > consistently.
> > > 
> > > How small are the frames in you test? What is the highest fps value in
> > > your test?
> > 
> > QVGA, don't know fps exactly, pretty high, between 20 and 60fps, I think. 
> > Just try different frams sizes, go down to 64x48 or something.
> 
> Testing of 960x243 frames at 30 fps has been done during all my previous
> tests. I didn't see any issues at 30 fps.

Ok, I've found the reason. Buffer number repeats, when there is an 
underrun, which is happening in my tests, when frames are arriving quickly 
enough, but the user-space is not fast enough to process them, e.g., when 
it is writing them to files over NFS or even just displaying on the LCD. 
Without your patch these underruns happen just as well, they just don't 
get recognised, because there's always one buffer delayed, so, the queue 
is never empty.

Dan, please add my

Reviewed-(and-tested-)by: Guennadi Liakhovetski <g.liakhovetski at gmx.de>

Thanks
Guennadi
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Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/