Hello,
here are my ideas on what is basically necessary to use FDT for U-Boot configuration. I tried to keep it simple:
- If CFG_FDT_ADDR is defined in the boards configuration file, the global variable "fdt", already used by the FDT command, will be set at compile time to that address:
#ifdef CFG_FDT_ADDR struct fdt_header *fdt = CFG_FDT_ADDR; else struct fdt_header *fdt = NULL; #endif
- In the early boot phase, before relocation, the FDT is checked and an error message printed in case it's not found or invalid:
CPU: MPC5200 v1.0, Core v1.1 at 396 MHz Bus 132 MHz, IPB 66 MHz, PCI 33 MHz FDT: FDT_ERR_BADMAGIC (or OK, or version number?)
At this level also the compatibility of the FDT tree could be checked using fdt_boardcheck().
- After relocation, the blob is copied into memory via fdt_open_into() to a defined place and "fdt" is updated accordingly. Not sure, what location in RAM to use, but it should fit into the existing scheme. Any recommendations?
- When U-Boot is up, "fdt" points to a valid FDT, e.g. "fdt addr" is not necessary.
- I think the basic mechanism should also work _without_ FDT commands (cmd_fdt.c, getting ride of quit some code).
- bootm should then automatically use the address of "fdt" to boot the kernel.
Some more comments. I realized rather heavy consistency checks on almost any public FDT function via fdt_check_header. I actually would prefer to have one extended check function at the beginning, which also ensures the compatibility with the board and reduce the other checks to just verify the magic number.
Other related issues? Do we also need to maintain a checksum of the blob? At least it's on Jerry's to-do list.
What do you think? I'm going to show a first patch soon.
Wolfgang.