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ARM: uniphier: add weird workaround code for LD20

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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>
This commit is contained in:
Masahiro Yamada 2017-05-12 22:49:02 +09:00
parent 8d3064d9a9
commit 45f41c134b
2 changed files with 16 additions and 0 deletions
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2
arch/arm/mach-uniphier/arm64/Makefile
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@ -9,5 +9,7 @@ obj-y += mem_map.o
ifdef CONFIG_ARMV8_MULTIENTRY
obj-y += smp.o smp_kick_cpus.o
obj-$(CONFIG_ARCH_UNIPHIER_LD20) += arm-cci500.o
else
obj-$(CONFIG_ARCH_UNIPHIER_LD20) += lowlevel_init.o
endif
endif

14
arch/arm/mach-uniphier/arm64/lowlevel_init.S Normal file
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@ -0,0 +1,14 @@
/*
* 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)