u-boot/arch/arm/mach-uniphier/arm64/lowlevel_init.S

/*
 * Copyright (C) 2017 Socionext Inc.
 *
 * SPDX-License-Identifier:	GPL-2.0+
 */

#include <linux/linkage.h>

ENTRY(lowlevel_init)
	/* LD20 needs the following code to boot.  I do not know why. */
	mrs	x0, sctlr_el1
	msr	sctlr_el1, x0
	ret
ENDPROC(lowlevel_init)
ARM: uniphier: add weird workaround code for LD20 When booting from ARM Trusted Firmware, U-Boot runs in EL1-NS. The boot flow is as follows: BL1 -> BL2 -> BL31 -> BL33 (i.e. U-Boot) This boot sequence works fine for LD11 SoC (Cortex-A53), but LD20 SoC (Cortex-A72) hangs in U-Boot. The solution I found is to read sctlr_el1 and write back the value as-is. This should be no effect, but surprisingly fixes the problem for LD20 to boot. I do not know why. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> 2017-05-12 13:49:02 +00:00			`/*`
			`* Copyright (C) 2017 Socionext Inc.`
			`*`
			`* SPDX-License-Identifier: GPL-2.0+`
			`*/`

			`#include <linux/linkage.h>`

			`ENTRY(lowlevel_init)`
			`/* LD20 needs the following code to boot. I do not know why. */`
			`mrs x0, sctlr_el1`
			`msr sctlr_el1, x0`
			`ret`
			`ENDPROC(lowlevel_init)`