[Bug 103844]=?UTF-8?Q?=20=E3=80=90braswell=E3=80=91?="*ERROR* cpu pipe A|B|C fifo underrun" - can not recovery

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103844

--- Comment #3 from ycui6 <yao.cui at intel.com> ---
Hi Elizabeth,
Yao is one PAE from Intel IOTG PRC ICE team. 
Kai reported issue come from DAHUA one big customer WW top 10 in DSS domain, I
assistant Kai on this underrun can't recovery issue for more than one weeks.
It's truly urgent to customer. Shall we improve this ticket priority?

BTW:
1, Kernel Update: 
1-1 Kai serviced project has pass production base on 4.2.x that is Brasewell 
suggested kernel that time and with https://www.kernel.org long term support.
It's not easy to update before that prove workable. BTW what version do u
suggest for BSW? 4.4 or 4.09/4.10?...

2, About Rootcause:

This issue happen with firstly 3 independence display refresh their monitors
highest timing. Almost 1080p60 fps, Secondly GFX media full-time running for 16
channelx1080p decoding or switch 3x4k, or 64xD1...and VPP combine them together
to 3 display channel, and maybe flip window would overlap each other. Thirdly,
PIPEA/C may show the same video source and display using set_plane for refresh
by only A's VBL(Potential SYNC Problem? But libdrm should help handle and
protect this).

On the other hand, we make a small test. found that if one FB is displaying on
one PIPE, and we thought it finished on other, we hard swith FB on the 2nd
pipe's regs, underrun also cold happen.

Another try, is when 3 independence display running normally. we try to
modified  FIFODISARB, to some level. underrun also could happen.


So question here, Expect for your sharing you Opinions
1,what's the truly root cause do u think that underrun happened 
  A, Memory Bandwidth?  
     then we try to workaround by slow down the FPS, or try cut-off some GFX
task
  B, FB switch by setplane. kernel sync protection is not good?
     then try upgrade kernel and try if already fix there
  c, HW FIFO by REG FIFODISARB not tuning to a suitable size?
     Still need turing.

We really need your help and comments. expect for your reply, thanks!

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