[U-Boot] [PATCH 1/2] rpi: save firmware provided boot param for later use

[Stephen Warren]

On 11/02/2016 12:06 PM, Cédric Schieli wrote:
> At U-Boot entry point, the r2 register holds the address of the
> firmware provided boot param. Let's save it for further processing.

> diff --git a/board/raspberrypi/rpi/lowlevel_init.S b/board/raspberrypi/rpi/lowlevel_init.S

> +.global fw_boot_param
> +fw_boot_param:
> +	.word 0x00000000

fw_dtb_pointer might be a better name; there are multiple different 
registers set up by the FW in some cases; best to be explicit about what 
kind of parameter is being saved.

See the note later about the size/alignment requirements for this value.

> +/*
> + * Routine: save_boot_params (called after reset from start.S)
> + * Description: save ATAG/FDT address provided by the firmware at boot time
> + */
> +
> +.global save_boot_params
> +save_boot_params:
> +
> +	/* The firmware provided ATAG/FDT address can be found in r2 */
> +	str	r2, fw_boot_param

For the 64-bit RPi builds, you need to save x0 not r2. The assembly 
above doesn't compile since r2 isn't a valid register (it's named x2 on 
64-bit), plus the DTB pointer is actually in x0 not x2.

> +	/* Returns */
> +	b	save_boot_params_ret

With these patches applied, the build of rpi_defconfig fails since the 
ARM1176 CPU startup file doesn't define that symbol.

> diff --git a/include/configs/rpi.h b/include/configs/rpi.h

> +#ifndef __ASSEMBLY__
> +/* Firmware provided boot param */
> +extern const void *fw_boot_param;
> +#endif

For the rpi_3 build, a void* is a 64-bit value, yet in lowlevel_init.S, 
it's defined a a .word (32-bit) rather than a .dword (64-bit).

I'd suggest adjusting the assembly file so that fw_boot_param is either 
a .word or a .dword depending on whether the code is being built for 
32-bit or 64-bit mode. That will allow the C definition to be identical 
across all RPi builds.

Note: In the .dword case the symbol must be aligned to 8-bytes, and it 
won't hurt in the 32-bit case; see the following patch:

https://patchwork.ozlabs.org/patch/684429/
ARM: tegra: ensure nvtboot_boot_x0 alignment