Hi Mario,
On 14 July 2017 at 05:55, Mario Six mario.six@gdsys.cc wrote:
Commit 2a79275 ("dm: Add callback to modify the device tree") implemented a board-specific callback that can modify U-Boot's device tree before relocation to accomodate a range of hardware variations of certain boards.
However, this approach only turns out to be useful when the copy of the device tree before relocation is actually writeable. If e.g. a device boots out of a NOR flash, this scheme does not work, since the modification of the flash's contents is not possible, and the unmodified device tree is relocated and used by U-Boot.
To circumvent this problem, we split the modification process into two phases.
In phase one we only collect information about the board by querying the hardware (reading GPIO values, probing I2C chips, etc.), and store the obtained information in a special, board-specific structure that is part of the global data structure. This phase runs prior to relocation, and utilizes the pre-relocation DM to query hardware information.
In phase two, we read the information back from the structure, and do the actual manipulation of the device tree. This phase occurs *after* the relocation of the U-Boot image, but before the driver model is initialized from the device tree. Since the device tree lives in RAM alongside the U-Boot image after relocation, the tree is definitely writeable at this point.
Each phase is implemented by a board-specific callback function: phase one by board_fix_fdt_get_info, which takes no arguments, and phase two by board_fix_fdt_change, which takes the writeable device tree blob as its sole argument. Since the structure where the gathered hardware information is stored is necessarily board-dependent, we create a include file where the boards utilizing the functionality can define their individually needed structures.
This commit also adapts the controlcenterdc board's fixup function to the new schem
Thanks for the clear explanation.
I have two ideas:
- Can we move the call to the existing function to after reloc_fdt(), when the DT is in RAM?
- Or can we move this board to use a livetree and adjust the DT using livetree functions instead? That might be more efficient.
Regards, Simon