[Bug 91926] [SKL bisected] texsubimage pbo intermittent failures

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91926

--- Comment #72 from Topi Pohjolainen <topi.pohjolainen at intel.com> ---
The final blit from the texture to the framebuffer is executed using
fixed-function fragment shader. I hacked Mesa to simulate the color values in
the test for R-component - the test uses values depending on the Y-component,
specifically R = 4 * y.
So I hacked Mesa to overwrite the R-component to 4 * y instead of using the
value read from the texture:

pln(8)          g127<1>F        g5.4<0,1,0>F    g2<8,8,1>F
pln(8)          g8<1>F          g6<0,1,0>F      g2<8,8,1>F
pln(8)          g9<1>F          g6.4<0,1,0>F    g2<8,8,1>F
pln(8)          g4<1>F          g7.4<0,1,0>F    g2<8,8,1>F
mul(8)          g124<1>F        g9<8,8,1>F      4F              
math inv(8)     g5<1>F          g4<8,8,1>F      null
mul(8)          g2<1>F          g8<8,8,1>F      g5<8,8,1>F
mul(8)          g3<1>F          g9<8,8,1>F      g5<8,8,1>F
send(8)         g2<1>UW         g2<8,8,1>F
   sampler sample SIMD8 Surface = 1 Sampler = 0 mlen 2 rlen 4 { align1 1Q };
mov(8)          g125<1>F        g3<8,8,1>F
mov(8)          g126<1>F        g4<8,8,1>F
sendc(8)        null            g124<8,8,1>F
   render RT write SIMD8 LastRT Surface = 0 mlen 4 rlen 0 { align1 1Q EOT };


With this I can get the same intermittent pixel failures I'm seeing without:

32:0:0:255 0:0:0:255 x=0 y=8 z=0
32:2:0:255 0:2:0:255 x=1 y=8 z=0
32:4:0:255 0:4:0:255 x=2 y=8 z=0
32:6:0:255 0:6:0:255 x=3 y=8 z=0
36:0:0:255 4:0:0:255 x=0 y=9 z=0
36:2:0:255 4:2:0:255 x=1 y=9 z=0
36:4:0:255 4:4:0:255 x=2 y=9 z=0
36:6:0:255 4:6:0:255 x=3 y=9 z=0
40:0:0:255 8:0:0:255 x=0 y=10 z=0
40:2:0:255 8:2:0:255 x=1 y=10 z=0
40:4:0:255 8:4:0:255 x=2 y=10 z=0
40:6:0:255 8:6:0:255 x=3 y=10 z=0
44:0:0:255 12:0:0:255 x=0 y=11 z=0
44:2:0:255 12:2:0:255 x=1 y=11 z=0
44:4:0:255 12:4:0:255 x=2 y=11 z=0
44:6:0:255 12:6:0:255 x=3 y=11 z=0

First four values are the expected, second four are the values read back. This
tells us that the problem isn't necessarily sampling - it looks that the
y-coordinate is being wrong during the tex-2-fb blit.

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