etnaviv: Beware of the PULSE_EATER

[Wladimir J. van der Laan]

Entirly deserving of its B-horror name it does unspeakable
things to performance if not set up correctly.

I was doing memory benchmarks and noticed a serious discrepancy
between running the same CL program with the Vivante driver
and replaying it on etnaviv.

After carefully comparing the registers written at initialization
with both kernel drivers, it became apparent that the etnaviv
DRM driver is not setting up register 0x0010C. Adding a single line
at the end of etnaviv_gpu_init sped up pure-read performance from shaders by
7.5x and write performance by 1.5x:

        gpu_write(gpu, VIVS_PM_PULSE_EATER, 0x015d0880);

(instead of this line we likely want to replicate viv_gpu's per-model logic)

Apart from silly CL benchmarks, I expect this to make a large impact with
texturing and alpha blending as well. Exact results for i.MX6qp (GC3000) below.

Wladimir

("readacc" does read-and-accumulate into register, "read" does only reads, "write"
does only writes, "ram" benchmarks DDR3 RAM, "ocram" i.MX6 onchip ram)

kernel 4.8.4 + etnaviv
----------------------

Version: 1.0.0
  Name: etnaviv
  Date: 20151214
  Description: etnaviv DRM
[read]    [ram]   Speed:  15.395 MB/s
[readacc] [ram]   Speed:  14.680 MB/s (compare to readacc4x_alt.cl below :( )
[write]   [ram]   Speed: 148.453 MB/s (compare to write4x_alt.cl below :( )
[read]    [ocram] Speed:  15.097 MB/s
[readacc] [ocram] Speed:  14.367 MB/s
[write]   [ocram] Speed: 148.419 MB/s

kernel 4.1.5 + viv_gpu
----------------------

[ram]
(no bench_read.cl: pure reads are optimized away by CL compiler)
Program: bench_readacc4x_alt.cl    Speed:  83.720 MB/s
Program: bench_write4x_alt.cl      Speed: 234.708 MB/s

etnaviv 4.8.4 after PULSE_EATER neutered
------------------------------------------

Version: 1.0.0
  Name: etnaviv
  Date: 20151214
  Description: etnaviv DRM
[read]    [ram]   Speed: 113.414 MB/s
[readacc] [ram]   Speed:  82.395 MB/s (comparable to readacc4x_alt.cl above)
[write]   [ram]   Speed: 234.955 MB/s (comparable to write4x_alt.cl above)
[read]    [ocram] Speed:  87.912 MB/s
[readacc] [ocram] Speed:  70.329 MB/s
[write]   [ocram] Speed: 234.956 MB/s