[PATCH 1/4] spl: atf: support Linux as BL33 with ATF

[Marek Vasut]

On 6/9/26 6:52 PM, Alexey Charkov wrote:
> Modern SoCs such as Rockchip RK3576 need ATF to be running to provide
> firmware services to the OS.
> 
> Enable the ATF boot flow to allow using Linux as BL33 (including its
> calling convention) to facilitate Falcon mode boot on such SoCs.

TFA

> +/* BL33 defaults to U-Boot unless Falcon mode selects Linux. */
> +static int spl_atf_bl33_os;
> +

Can we avoid this global static variable ?

>   /* Holds all the structures we need for bl31 parameter passing */
>   struct bl2_to_bl31_params_mem {
>   	struct bl31_params bl31_params;
> @@ -87,8 +90,11 @@ struct bl31_params *bl2_plat_get_bl31_params_default(ulong bl32_entry,
>   	SET_PARAM_HEAD(bl33_ep_info, ATF_PARAM_EP, ATF_VERSION_1,
>   		       ATF_EP_NON_SECURE);
>   
> -	/* BL33 expects to receive the primary CPU MPID (through x0) */

That seems a bit inconsistent, and not quite right. Do you know where 
U-Boot expects primary CPU ID in x0 exactly ? Which part of U-Boot code 
depends on it ?

> -	bl33_ep_info->args.arg0 = 0xffff & read_mpidr();
> +	/* Linux-at-BL33 expects DTB in x0, U-Boot expects primary CPU MPID in x0. */
> +	if (IS_ENABLED(CONFIG_SPL_OS_BOOT) && spl_atf_bl33_os == IH_OS_LINUX)
> +		bl33_ep_info->args.arg0 = fdt_addr;
> +	else
> +		bl33_ep_info->args.arg0 = 0xffff & read_mpidr();

[...]

> @@ -269,15 +279,22 @@ void __noreturn spl_invoke_atf(struct spl_image_info *spl_image)
>   		bl32_entry = spl_fit_images_get_entry(blob, node);
>   
>   	/*
> -	 * Find the U-Boot binary (in /fit-images) load addreess or
> -	 * entry point (if different) and pass it as the BL3-3 entry
> -	 * point.
> -	 * This will need to be extended to support Falcon mode.
> +	 * Find BL33 entry point. In Falcon mode, prefer Linux when requested.
> +	 * Fall back to U-Boot if Linux cannot be resolved.
That does not seem correct, if Linux cannot be resolved, then the system 
should stop booting, falling back into a bootloader could be security 
risk. There is a "recovery" boot weak symbol function, which can be used 
to start fallback bootloader, but that has to be deliberately 
implemented and triggered by the user e.g. by holding a button down.