Oftree from memory and access to start arguments

Sascha Hauer s.hauer at pengutronix.de
Thu Jun 7 00:31:13 PDT 2018


Hi Pascal,

On Wed, Jun 06, 2018 at 01:07:27AM +0200, Pascal Vizeli wrote:
> Hi,
> 
> I'm working on a functionality to load a device tree with oftree from
> memory. The use case is like raspberry platform they have his own
> device tree for linux kernel. If I known the address (config.txt), I
> will load this from memory and read out the dynamic linux args and use
> other overlays for states with bootchoiser and boot the kernel
> correctly.
> 
> On raspberry, I can write the device-tree to a memory address with
> config.txt. It would be nice, if I can access to barebox (start.c)
> main arguments, while the raspberry pi load barebox like a linux
> kernel and give him the device-address on r2.

Starting barebox with the devicetree provided in r2 shouldn't be a
problem. See arch/arm/boards/raspberry-pi/lowlevel.c:

ENTRY_FUNCTION(start_raspberry_pi2, r0, r1, r2)
{
        void *fdt = __dtb_bcm2836_rpi_2_start + get_runtime_offset();

        arm_cpu_lowlevel_init();

        barebox_arm_entry(BCM2835_SDRAM_BASE, SZ_512M, fdt);
}

Just call barebox_arm_entry() with 'r2' instead of 'fdt'.

You could also store the value of r2 in a known memory location
and load the devicetree later in some board specific initcall.

Sascha

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