[BUG 4.17] etnaviv-gpu f1840000.gpu: recover hung GPU!

[Russell King - ARM Linux]

It looks like a bug has crept in to etnaviv between 4.16 and 4.17,
which causes etnaviv to misbehave with the GC600 GPU on Dove.  I
don't think it's a GPU issue, I think it's a DRM issue.

I get multiple:

[  596.711482] etnaviv-gpu f1840000.gpu: recover hung GPU!
[  597.732852] etnaviv-gpu f1840000.gpu: GPU failed to reset: FE not idle, 3D not idle, 2D not idle

while Xorg is starting up.  Ignore the "failed to reset", that
just seems to be a property of the GC600, and of course is a
subsequent issue after the primary problem.

Looking at the devcoredump:

00000004 = 000000fe Idle: FE- DE+ PE+ SH+ PA+ SE+ RA+ TX+ VG- IM- FP- TS-

So, all units on the GC600 were idle except for the front end.

00000660 = 00000812 Cmd: [wait DMA: idle Fetch: valid] Req idle Cal idle
00000664 = 102d06d8 Command DMA address
00000668 = 380000c8 FE fetched word 0
0000066c = 0000001f FE fetched word 1

The front end was basically idle at this point, at a WAIT 200 command.
Digging through the ring:

00688: 08010e01 00000040  LDST 0x3804=0x00000040
00690: 40000002 102d06a0  LINK 0x102d06a0
00698: 40000002 102d0690  LINK 0x102d0690
006a0: 08010e04 0000001f  LDST 0x3810=0x0000001f
006a8: 40000025 102d3000  LINK 0x102d3000
006b0: 08010e03 00000008  LDST 0x380c=0x00000008 Flush PE2D
006b8: 08010e02 00000701  LDST 0x3808=0x00000701 SEM FE -> PE
006c0: 48000000 00000701  STALL FE -> PE
006c8: 08010e01 00000041  LDST 0x3804=0x00000041
006d0: 380000c8(0000001f) WAIT 200
006d8: 40000002 102d06d0  LINK 0x102d06d0	 <===========

We've basically come to the end of the currently issued command stream
and hit the wait-link loop.  Everything else in the devcoredump looks
normal.

So, I think etnaviv DRM has missed an event signalled from the GPU.

This worked fine in 4.16, so seems to be a regression.

-- 
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