[U-Boot] P2020 SPL L2 clearing

[Fabian Cenedese <Cenedese@indel.ch>]

At 14:17 03.02.2011 +0100, Fabian Cenedese wrote:
>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 mpc85xx 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 with P2020).
>
>2. Why does the cache to be cleared at 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.

I just wanted to ask again if somebody has any insight
on this. Maybe Kumar?

Thanks

bye  Fabi