[Intel-gfx] [PATCH] Watermark level workaround for i830

[Daniel Vetter]

On Tue, Nov 19, 2013 at 10:55 AM, Thomas Richter <thor at math.tu-berlin.de> wrote:
> In the meantime, I also checked with video overlays, and the minimum value
> of 6 is not yet quite optimal, higher values (lower watermarks) seem to do
> even better. From the values I get, I also estimate a minimum latency of
> about 1100 ns, the default value of 5000 is much too high for the i830.
>
> There are two alternative possibilities to fix this:
>
> a) Include in the watermark structure not only a maximum value, but also a
> minimum value and modify calculate_wm accordingly,

I think this is what we need - Bspec explicitly mentions that setting
the watermark so that the fifo could overrun with the given burst
length is a bad idea. Atm we set the brust length to 8, so my standing
bet is that this is the limit where things start to get fully stable.

I've started to work on patches for this last w/e but got distracted a
bit with my real job, hence the silence.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch