Hi Dirk, On Sat, Mar 24, 2012 at 11:59 PM, Dirk Behme <dirk.be...@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=8c644b7dacdc9b7a196a5238f4dc5d94bd615d07;hb=HEAD#l1285 > > [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_rw.c;h=5c27a677e3536ed7320ee399113666975e5d545b;hb=HEAD#l127 > _______________________________________________ > U-Boot mailing list > U-Boot@lists.denx.de > http://lists.denx.de/mailman/listinfo/u-boot _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
