On 2016-05-27 02:13, Maxime Ripard wrote:
> The device tree overlays are a good way to deal with user-modifyable
> boards or boards with some kind of an expansion mechanism where we can
> easily plug new board in (like the BBB or the raspberry pi).
>
> However, so far, the usual mechanism to deal with it was to have in Linux
> some driver detecting the expansion boards plugged in and then request
> these overlays using the firmware interface.
>
> That works in most cases, but in some cases, you might want to have the
> overlays applied before the userspace comes in. Either because the new
> board requires some kind of an early initialization, or because your root
> filesystem is accessed through that expansion board.
>
> The easiest solution in such a case is to simply have the component before
> Linux applying that overlay, removing all these drawbacks.
>
> Signed-off-by: Maxime Ripard <maxime.rip...@free-electrons.com>
> ---
> cmd/fdt.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
Reviewed-by: Stefan Agner <ste...@agner.ch>
>
> diff --git a/cmd/fdt.c b/cmd/fdt.c
> index 0f5923e75a41..6cbc9e525d6c 100644
> --- a/cmd/fdt.c
> +++ b/cmd/fdt.c
> @@ -639,6 +639,25 @@ static int do_fdt(cmd_tbl_t *cmdtp, int flag, int
> argc, char * const argv[])
> #endif
>
> }
> + /* apply an overlay */
> + else if (strncmp(argv[1], "ap", 2) == 0) {
> + unsigned long addr;
> + struct fdt_header *blob;
> +
> + if (argc != 3)
> + return CMD_RET_USAGE;
> +
> + if (!working_fdt)
> + return CMD_RET_FAILURE;
> +
> + addr = simple_strtoul(argv[2], NULL, 16);
> + blob = map_sysmem(addr, 0);
> + if (!fdt_valid(&blob))
> + return CMD_RET_FAILURE;
> +
> + if (fdt_overlay_apply(working_fdt, blob))
> + return CMD_RET_FAILURE;
> + }
> /* resize the fdt */
> else if (strncmp(argv[1], "re", 2) == 0) {
> fdt_shrink_to_minimum(working_fdt);
> @@ -1025,6 +1044,7 @@ static int fdt_print(const char *pathp, char
> *prop, int depth)
> #ifdef CONFIG_SYS_LONGHELP
> static char fdt_help_text[] =
> "addr [-c] <addr> [<length>] - Set the [control] fdt location to
> <addr>\n"
> + "fdt apply <addr> - Apply overlay to the DT\n"
> #ifdef CONFIG_OF_BOARD_SETUP
> "fdt boardsetup - Do board-specific set up\n"
> #endif
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