[PATCH 1/5] mips: start.S: Add Octeon boot header compatibility

[Stefan Roese]

On 26.10.20 14:42, Daniel Schwierzeck wrote:
> Am Freitag, den 16.10.2020, 15:08 +0200 schrieb Stefan Roese:
>> Octeon has a specific boot header, when booted via SPI NOR, NAND or MMC.
>> Here the only 2 instructions are allowed in the first few bytes of the
>> image. And these instructions need to be one branch and a nop. This
>> patch adds the necessary nop after the nop, to that the common MIPS
>> image is compatible with this Octeon header.
>>
>> The tool to patch the Octeon boot header into the image will be send in
>> a follow-up patch.
>>
>> Signed-off-by: Stefan Roese <sr at denx.de>
>> Cc: Aaron Williams <awilliams at marvell.com>
>> Cc: Chandrakala Chavva <cchavva at marvell.com>
>> Cc: Daniel Schwierzeck <daniel.schwierzeck at gmail.com>
>> ---
>>   arch/mips/cpu/start.S | 8 +++++++-
>>   1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/mips/cpu/start.S b/arch/mips/cpu/start.S
>> index d0c412236d..6de2470cc2 100644
>> --- a/arch/mips/cpu/start.S
>> +++ b/arch/mips/cpu/start.S
>> @@ -75,8 +75,13 @@
>>   
>>   ENTRY(_start)
>>   	/* U-Boot entry point */
>> +	/*
>> +	 * Octeon needs special handling here, as the binary might be
>> +	 * patched to add a boot header for SPI, NAND or MMC booting. Only
>> +	 * one branch plus nop is allowed here.
>> +	 */
> 
> I'd prefer a shorter and more imperative comment within one multi-line
> comment block, e.g.
> 
> /*
>   * U-Boot entry point.
>   * Do not add instructions to the branch delay slot! Some SoC's
>   * like Octeon might patch the final U-Boot binary at this location
>   * with additional boot headers.
>   */

Even better. Will change in v2.

>>   	b	reset
>> -	 mtc0	zero, CP0_COUNT	# clear cp0 count for most accurate boot timing
>> +	 nop
>>   
>>   #if defined(CONFIG_MIPS_INSERT_BOOT_CONFIG)
>>   	/*
>> @@ -123,6 +128,7 @@ ENTRY(_start)
>>   #endif
>>   
>>   reset:
>> +	 mtc0	zero, CP0_COUNT	# clear cp0 count for most accurate boot timing
> 
> the extra indentation of one space is only required for instructions in
> delay slots and needs to be removed.

Yes, thanks for catching.

Thanks,
Stefan