[U-Boot] [PATCH] ARM: socfpga: Add boot0 hook to prevent SPL corruption

[Marek Vasut]

On 11/16/2016 08:27 PM, Dinh Nguyen wrote:
> 
> 
> On 11/16/2016 10:54 AM, Marek Vasut wrote:
>> Valid Altera SoCFPGA preloader image must contain special data at
>> offsets 0x40, 0x44, 0x48 and valid instructions at address 0x4c or
>> 0x50. These addresses are by default used by U-Boot's vector table
>> and a piece of reset handler, thus a valid preloader corrupts those
>> addresses slightly. While this works most of the time, this can and
>> does prevent the board from rebooting sometimes and triggering this
>> issue may even depend on compiler.
>>
>> The problem is that when SoCFPGA performs warm reset, it checks the
>> addresses 0x40..0x4b in SRAM for a valid preloader signature and
>> header checksum. If those are found, it jumps to address 0x4c or
>> 0x50 (this is unclear). These addresses are populated by the first
>> few instructions of arch/arm/cpu/armv7/start.S:
>>
>> ffff0040 <data_abort>:
>> ffff0040:       ebfffffe        bl      ffff0040 <data_abort>
>>
>> ffff0044 <reset>:
>> ffff0044:       ea000012        b       ffff0094 <save_boot_params>
>>
>> ffff0048 <save_boot_params_ret>:
>> ffff0048:       e10f0000        mrs     r0, CPSR
>> ffff004c:       e200101f        and     r1, r0, #31
>> ffff0050:       e331001a        teq     r1, #26
>>
>> Without this patch, the CPU will enter the code at 0xffff004c or
>> 0xffff0050 , at which point the value of r0 and r1 registers is
>> undefined. Moreover, jumping directly to the preloader entry point
>> at address 0xffff0000 will also fail, because address 0xffff004.
>> is invalid and contains the preloader magic.
>>
>> Add BOOT0 hook which reserves the area at offset 0x40..0x5f and
>> populates offset 0x50 with jump to the entry point. This way, the
>> preloader signature is stored in reserved space and can not corrupt
>> the SPL code.
>>
>> Signed-off-by: Marek Vasut <marex at denx.de>
>> Cc: Chin Liang See <clsee at altera.com>
>> Cc: Dinh Nguyen <dinguyen at opensource.altera.com>
>> Cc: Stefan Roese <sr at denx.de>
>> ---
>>  arch/arm/Kconfig                           |  1 +
>>  arch/arm/mach-socfpga/include/mach/boot0.h | 28 ++++++++++++++++++++++++++++
>>  2 files changed, 29 insertions(+)
>>  create mode 100644 arch/arm/mach-socfpga/include/mach/boot0.h
> 
> With this patch, I can properly do a soft reset on an Atlas DE0 Nano board.
> 
> So feel free to add:
> 
> Tested-by: Dinh Nguyen <dinguyen at opensource.altera.com>

That's great, thanks for checking ! You probably want to propagate this
fix to your downstream U-Boot mutation and also that MPL loader.

-- 
Best regards,
Marek Vasut