[PATCH] stm32mp2: update register used by BL31 for boot parameter

[Patrice CHOTARD]

On 9/17/25 14:31, Patrick Delaunay wrote:
> Use the ARM64 kernel booting register settings, defined in Linux
> documentation Documentation/arch/arm64/booting.rst:
> 
>  x0 = physical address of device tree blob (dtb) in system RAM.
> 
> so kernel can replace U-Boot in FIP without modification of BL31.
> 
> Use x0 for future TF-A version and keep x2 as fallback to be compatible
> with previous version of TF-A BL31.
> 
> Signed-off-by: Patrick Delaunay <patrick.delaunay at foss.st.com>
> ---
> 
>  arch/arm/mach-stm32mp/stm32mp2/cpu.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/mach-stm32mp/stm32mp2/cpu.c b/arch/arm/mach-stm32mp/stm32mp2/cpu.c
> index c3b87d7f9810..e081dc605b84 100644
> --- a/arch/arm/mach-stm32mp/stm32mp2/cpu.c
> +++ b/arch/arm/mach-stm32mp/stm32mp2/cpu.c
> @@ -92,13 +92,21 @@ uintptr_t get_stm32mp_bl2_dtb(void)
>  }
>  
>  /*
> - * Save the FDT address provided by TF-A in r2 at boot time
> + * Save the FDT address provided by TF-A at boot time
>   * This function is called from start.S
>   */
> -void save_boot_params(unsigned long r0, unsigned long r1, unsigned long r2,
> -		      unsigned long r3)
> +void save_boot_params(unsigned long x0, unsigned long x1, unsigned long x2,
> +		      unsigned long x3)
>  {
> -	nt_fw_dtb = r2;
> +	/* use the ARM64 kernel booting register settings:
> +	 * x0 = physical address of device tree blob (dtb) in system RAM.
> +	 * so kernel can replace U-Boot in FIP wihtout BL31 modification
> +	 * else falback to x2 used in previous TF-A version
> +	 */
> +	if (x0)
> +		nt_fw_dtb = x0;
> +	else
> +		nt_fw_dtb = x2;
>  
>  	save_boot_params_ret();
>  }

Reviewed-by: Patrice Chotard <patrice.chotard at foss.st.com>

Thanks
Patrice