[Bug 97965] [BSW] External HDMI monitor suddenly shows solid color when playing Youtube video at 1080p [fifo underrun]

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97965

--- Comment #52 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
There are a lot of knobs in the Bunit that might be of interest. I did a quick
trawl through the registers and came up with the following list:

BARBCTL0 0x3
BARBCTL2 0x4
BARBCTL3 0x5
BARBCTL4 0x6
 for each agent
 [5:0] arbiter weight
 [7:6] reserved

COSCAT 0x12
 for each agent 
 [1:0] COS category (0x0=normal, 0x1=isoc, others=reserved)

BALIMIT0 0xb
BALIMIT1 0xc
BALIMIT2 0xd
BALIMIT3 0xe
 for each agent
 [5:0] limit if some sort
 [7:6] reserved

BFLWT 0x14
 [5:0] read weights
 [13:8] write weights

BISOCWT 0x16
 [5:0] non-isoc weights
 [13:8] isoc weights
 [31] enable isoc weights

There are 16 agents possible it seems (agent0 to agent15). I get the
impression that display is agent3, but there was one note somewhere
about display possibly being agent2. But by default agent2 is not isoc whereas
agent3 is, so that makes me think agent3 is more likely.

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