On Fri, 30 Sep 2022 18:36:31 +0200, Rafał Miłecki wrote:
From: Rafał Miłecki rafal@milecki.pl
Broadcom uses U-Boot for a lot of their bcmbca familiy chipsets. U-Boot stores its configuration in an environment data block.
Such blocks are usually stored on flash as a separated partition at hardcoded address. Broadcom however decided to:
- Store env data block inside U-Boot partition
- Avoid sticking to hardcoded offsets
- Use custom header with "uEnv" magic and env data length
Example (length 0x4000): $ hexdump -n 32 -C -s 0x40000 /dev/mtdblock0 00040000 76 6e 45 75 00 40 00 00 34 89 7a 82 49 4d 41 47 |vnEu.@..4.z.IMAG| 00040010 45 3d 4e 41 4e 44 3a 31 4d 2c 31 30 32 34 4d 00 |E=NAND:1M,1024M.| (0x40000 offset is unit specific and can change)
Starting with the commit 118f3fbe517f4 ("dt-bindings: mtd: partitions: support label/name only partition") DT can describe partitions matching them by a name (without specifying actual address). With that feature and this binding change it's possible to:
- Specify DT node for Broadcom's U-Boot env data subpartition
- Add nodes for specific environment data variables
- Reference them as NVMEM cells
This binding is unlikely to help Broadcom's U-Boot. U-Boot SPL needs to find environment data early (before it accesses DTB) and it does that by looking for an "uEnv" magic. Dirty way.
This binding can however be used by operating systems. It allows describing cleanly U-Boot, its env data and variables. It tells operating system about Broadcom-specific env data so it can parse it.
Signed-off-by: Rafał Miłecki rafal@milecki.pl
V2: Work on better commit body & add example
.../devicetree/bindings/nvmem/u-boot,env.yaml | 21 +++++++++++++++++++ 1 file changed, 21 insertions(+)
Applied, thanks!