[U-Boot] NAND bootloader, SPL<->NUB offset for large page NAND

[Scott Wood]

On Fri, Apr 16, 2010 at 01:29:26PM +0200, Peter Vollmer wrote:
> Hi,
> 
> I have a question regarding the usage of CPU's with the Freescale ELBC  
> nand controller, in my case a MPC8313, and large page NAND (i.e.pagesize =  
> 2048+64 bytes, blocksize = 128k):
> 
> In nand_spl/nand_boot_fsl_elbc.c , static void nand_load(unsigned int  
> offs, int uboot_size, uchar *dst) first does a check if the given offset  
> to the NUB part of the bootloader is one block, i.e. 128 k in case of  
> large page NAND.
> 
> ...
> if (offs & (block_size - 1)) {
> 	puts("bad offset\n");
> 	for (;;);
> }
> ...
> 
> Is this offset of one block really necessary?

Without it we'd need to special-case the bad block handling.

> AFAIU the SPL bootloader  
> needs to fit into the 4-Kbyte SPL boot block for execute-in-place boot  
> loading.
> I could imagine to just use the remaining ~124k of the first block  
> (guaranteed to be valid for large page NAND) for a good part of the NUB  
> part of the bootloader. The bad-block skipping part would become effective  
> for the following blocks nevertheless. Is there a reason to have the NUB  
> part start in its own NAND block ?

We do use the remaining 124 KiB for the payload -- see e.g. MPC8536DS.h.  We
just set CONFIG_SYS_NAND_U_BOOT_OFFS to zero, and
CONFIG_SYS_NAND_U_BOOT_START to 4KiB after the destination.  The SPL will be
loaded twice, but who cares?

-Scott