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fel-sdboot: Fix header corruption workaround, implement in assembly

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Now that we have a better understanding of what's causing the issue
that prevented entering FEL sometimes, we can adjust the workaround
code to a proper solution, i.e. skip over the problematic location.

Since the code amounts to less than a dozen ARM instructions, I've
decided to rewrite it as assembly code - fel-sdboot.S replaces the
former fel-sdboot.c.

The commit also includes a new binary (bin/fel-sdboot.sunxi) with
these changes.

Signed-off-by: Bernhard Nortmann <bernhard.nortmann@web.de>
Reviewed-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
This commit is contained in:
Bernhard Nortmann 2016-05-28 12:26:49 +02:00
parent ce9cf33606
commit 17164d8d9a
4 changed files with 70 additions and 60 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
Makefile
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@ -135,7 +135,7 @@ fel-pio.nm: fel-pio.elf
jtag-loop.elf: jtag-loop.c jtag-loop.lds
$(CROSS_COMPILE)gcc -g $(ARM_ELF_FLAGS) $< -nostdlib -o $@ -T jtag-loop.lds -Wl,-N
fel-sdboot.elf: fel-sdboot.c fel-sdboot.lds
fel-sdboot.elf: fel-sdboot.S fel-sdboot.lds
$(CROSS_COMPILE)gcc -g $(ARM_ELF_FLAGS) $< -nostdlib -o $@ -T fel-sdboot.lds -Wl,-N
boot_head_sun3i.elf: boot_head.S boot_head.lds

BIN
bin/fel-sdboot.sunxi
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Binary file not shown.

69
fel-sdboot.S Normal file
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@ -0,0 +1,69 @@
/*
* Copyright (C) 2016 Bernhard Nortmann <bernhard.nortmann@web.de>
*
* Based on previous works
* Copyright (C) 2016 Siarhei Siamashka <siarhei.siamashka@gmail.com>
* Copyright (C) 2012 Henrik Nordstrom <henrik@henriknordstrom.net>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*
*/
/*
* This file is a utility stub (bootloader code) to force the device into
* FEL mode, by jumping directly to the corresponding (N-)BROM entry point.
*
* Build instructions:
* make fel-sdboot.sunxi
*
* If needed, adjust CROSS_COMPILE and MKSUNXIBOOT according to your
* toolchain, e.g.
* make fel-sdboot.sunxi CROSS_COMPILE=armv7a-hardfloat-linux-gnueabi- \
* MKSUNXIBOOT=/usr/local/bin/mksunxiboot
*
*
* Install instructions:
* dd if=fel-sdboot.sunxi of=/dev/sdX bs=1024 seek=8
*/
SCTRL .req r0
.equ V_BIT, (1 << 13)
.equ BROM_ENTRY_LOW, 0x00000020
.equ BROM_ENTRY_HIGH, 0xFFFF0020
/*
* In cases where insufficient padding is added by an old mksunxiboot,
* _start may be 0x20, which means that the instruction at 0x28 could get
* corrupted by the BROM - see https://patchwork.ozlabs.org/patch/622173/
*
* Apply a workaround to avoid (= skip over) that memory location.
* _main would be at 0x30 in that particular case. With newer (properly
* fixed) versions of mksunxiboot, this code ends up at higher addresses
* and will be moot, but harmless.
*/
_start:
b _main
nop
nop
nop
_main:
mrc p15, 0, SCTRL, c1, c0, 0
tst SCTRL, #V_BIT @ test SCTRL.V
moveq lr, #BROM_ENTRY_LOW
ldrne lr, =BROM_ENTRY_HIGH
bx lr

59
fel-sdboot.c
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@ -1,59 +0,0 @@
/*
* (C) Copyright 2011 Henrik Nordstrom <henrik@henriknordstrom.net>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*/
/*
Build instructions:
arm-none-linux-gnueabi-gcc -g -Os -fno-common -ffixed-r8 -msoft-float -fno-builtin -ffreestanding -nostdinc -mno-thumb-interwork -Wall -Wstrict-prototypes -fno-stack-protector -Wno-format-nonliteral -Wno-format-security -fno-toplevel-reorder fel-boot.c -c
arm-none-linux-gnueabi-objcopy -O binary fel-boot.o fel-boot.bin
mksunxiboot fel-boot.bin fel-boot.sunxi
Install instructions:
dd if=fel-boot.sunxi of=/dev/sdX bs=1024 seek=8
*/
void _start(void)
{
unsigned int sctlr;
/*
* FEL mode fails to activate in an unpredictable way without
* this NOP padding. Minor changes in the code, such as checking
* the PC register (PC >= 0x10000) instead of SCTLR.V or doing
* jump instead of call to the FEL handler in the BROM sometimes
* break on A64 and sometimes break on A10/A13/A20. Trying to
* add DSB & ISB instructions and/or invalidating caches and
* BTB do not seem to make any difference. Only adding a bunch
* of NOP instructions in the beginning helps.
*/
asm volatile(".rept 32 \n nop \n .endr");
asm volatile("mrc p15, 0, %0, c1, c0, 0" : "=r" (sctlr));
if (sctlr & (1 << 13)) /* SCTLR.V */
((void (*)(void))0xffff0020)();
else
((void (*)(void))0x00000020)();
}