[Buildroot] [PATCH 4/8] boot/arm-trusted-firmware: add EDK2 as BL33 option

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello,

+Yann Morin, on variable reference between packages.

On Sun, 19 Jul 2020 18:10:03 +0000
Dick Olsson <hi@senzilla.io> wrote:

> diff --git a/boot/arm-trusted-firmware/Config.in b/boot/arm-trusted-firmware/Config.in
> index 7d0f6aa4e0..f24813f8e6 100644
> --- a/boot/arm-trusted-firmware/Config.in
> +++ b/boot/arm-trusted-firmware/Config.in
> @@ -1,7 +1,7 @@
>  config BR2_TARGET_ARM_TRUSTED_FIRMWARE
>  	bool "ARM Trusted Firmware (ATF)"
>  	depends on (BR2_ARM_CPU_ARMV8A || BR2_ARM_CPU_ARMV7A) && \
> -           BR2_TARGET_UBOOT
> +           (BR2_TARGET_UBOOT || BR2_TARGET_EDK2)

Ah, this is why your previous patch has a spurious change in this file :-)

> +config BR2_TARGET_ARM_TRUSTED_FIRMWARE_EDK2_AS_BL33
> +	bool "Use EDK2 as BL33"
> +	depends on BR2_TARGET_EDK2
> +	help
> +	  This option allows to embed EDK2 as the BL33 part of
> +	  the ARM Trusted Firmware. It ensures that the EDK2 package
> +	  gets built before ATF, and that the appropriate BL33
> +	  variable pointing to the EDK2 is passed when building ATF.
> +
> +	  Do not choose this option if you intend to build ATF and EDK2
> +	  for the 'qemu_sbsa' platform. In this case, due to the EDK2
> +	  build system, the dependency between ATF and EDK is reversed.

So there are cases where ATF depends on EDK2, and other cases where
EDK2 depends on ATF (BR2_TARGET_EDK2_PLATFORM_QEMU_SBSA situation).
Correct ?

Note: this is OK, we already have this situation between U-Boot and
ATF. On some platforms, ATF embeds U-Boot, on others, U-Boot embeds ATF.

>  config BR2_TARGET_ARM_TRUSTED_FIRMWARE_UBOOT_AS_BL33
>  	bool "Use U-Boot as BL33"
>  	depends on BR2_TARGET_UBOOT
> diff --git a/boot/arm-trusted-firmware/arm-trusted-firmware.mk b/boot/arm-trusted-firmware/arm-trusted-firmware.mk
> index a3553e36cf..58b48df5d8 100644
> --- a/boot/arm-trusted-firmware/arm-trusted-firmware.mk
> +++ b/boot/arm-trusted-firmware/arm-trusted-firmware.mk
> @@ -79,6 +79,13 @@ ARM_TRUSTED_FIRMWARE_MAKE_OPTS += AARCH32_SP=optee
>  endif
>  endif # BR2_TARGET_ARM_TRUSTED_FIRMWARE_BL32_OPTEE
>  
> +ifeq ($(BR2_TARGET_ARM_TRUSTED_FIRMWARE_EDK2_AS_BL33),y)
> +ARM_TRUSTED_FIRMWARE_DEPENDENCIES += edk2
> +# Since the flash device names vary between platforms, we use the variable
> +# provided by the EDK2 package this.
> +ARM_TRUSTED_FIRMWARE_MAKE_OPTS += BL33=$(BINARIES_DIR)/$(EDK2_FD_NAME).fd

So there is this reference to a variable of another package, which I'm
never sure if it works correctly. Yann, what is the rule again ? :-)

For the U-Boot case, we have an explicit
BR2_TARGET_ARM_TRUSTED_FIRMWARE_UBOOT_BL33_IMAGE. If we drop the
"platform choice" in EDK2, we would anyway have to specify somewhere a
free form string that contains the final image name.

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com