[U-Boot] P2020 SPL L2 clearing

[Fabian Cenedese <Cenedese@indel.ch>]

Hi

I'm creating a SPL u-boot image for our board. In the file
arch/powerpc/cpu/mpc85xx/cpu_init_nand.c is the setup for
the L2 cache as SRAM. In the end is a loop that fills the
cache with 0 (512KB in this case).

	/* Initialize L2 SRAM to zero */
	l2srbar = (char *)CONFIG_SYS_INIT_L2_ADDR;
	for (i = 0; i < CONFIG_SYS_L2_SIZE; i++)
		l2srbar[i] = 0;

Two questions for this:

1. Why is the access byte-wise and not dword-wise? This
is only for mpx85xx and I think they all can access the cache
with 32bits instead of just 8. That would speed up by factor 4
(confirmed in my tests).

2. Why does the cache to be cleared@all? L2-SRAM is usually
just used to copy in the second part of the u-boot image, so
the 0s will be overwritten again anyway.

I came to this loop because the board takes an awful long
time to boot up. I'm measuring now cpu ticks until board_init_r
(in the first part loader before the u-boot image gets loaded).
With this loop it takes about 4 seconds, without just 50 ms.
How come the L2 access is so slow? I already increased
the lb clock but that only helps "outside". Even if this loop
didn't need any time I'd still have the questions above.

Thanks

bye  Fabi