Hi Dirk,

On Sat, Mar 24, 2012 at 11:59 PM, Dirk Behme dirk.behme@googlemail.com wrote:

In boot_relocate_fdt() [1] we increase the size of the loaded fdt by a predefined, hard coded CONFIG_SYS_FDT_PAD. The basic idea seem to be to create some space for adding additional information later, like the bootargs.

I wonder why we have to do this by a hard coded, predefined value (which is most probably always to large)? Why can't we increase 'totalsize' in the fdt_header just if we add anything? Individually by the size of the element added, at runtime? E.g. by anything like [2]?

I debugged a system were

#define CONFIG_SYS_FDT_PAD 0x3000

was used. These 0x3000 are added to totalsize before something is added at all. Then, if an element is added, always the whole 0x3000 bytes have to be memmoved additionally. And in the end only ~0x100 additional space was really needed.

I don't really know the answer, but I guess that just increasing the FDT is dangerous, since we don't know how big it can grow before running into something else. This way we set a maximum size that it can grow to and will produce an error if it is exceeded.

There is also the practical problem that we would need to check for FDT_ERR_NOSPACE, expand the space, and then retry. A bit of a hassle...

I suppose you could use fdt_pack() afterwards, although I don't see a command for this at present.

Regards, Simon

Best regards

Dirk

[1] http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=blob;f=common/image.c;h...

[2]

static int _fdt_splice_struct(void *fdt, void *p,                              int oldlen, int newlen) {        int delta = newlen - oldlen;        int err;

if ((err = _fdt_splice(fdt, p, oldlen, newlen)))                return err;

fdt_set_size_dt_struct(fdt, fdt_size_dt_struct(fdt) + delta);        fdt_set_off_dt_strings(fdt, fdt_off_dt_strings(fdt) + delta);

• fdt_set_totalsize(fdt, fdt_totalsize(fdt) + delta);

return 0; }

in

http://git.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=blob;f=lib/libfdt/fdt_r... _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot