i.MX8MP SPL failures due to memory corruption/overflow?

[Frieder Schrempf]

On 15.03.23 15:17, Michael Nazzareno Trimarchi wrote:
> Hi
> 
> On Wed, Mar 15, 2023 at 3:13 PM Frieder Schrempf
> <frieder.schrempf at kontron.de> wrote:
>>
>> Hi,
>>
>> I'm trying to bring up a new board based on the i.MX8MP and I have an
>> issue I'm hoping someone can help solving.
>>
>> I'm seeing failures in the early SPL code, usually in the DDR
>> initialization. Often they look like:
>>
>>   U-Boot SPL 2023.04-rc3 (Mar 07 2023 - 14:32:34 +0000)
>>   Training FAILED
>>   Failed to initialize DDR RAM!
>>   ### ERROR ### Please RESET the board ###
>>
>> But sometimes ddr_init() doesn't even return an error and only the
>> get_ram_size() afterwards which tries to allocate the memory fails.
>>
> 
> In my experience you don't have space inside the cpu internal memory. It means
> that you overlap some stack with the code. Change the printf means
> move a bit. So you have
> problem but depends what you are going to destroy

Thanks for your reply. That's exactly what I'm thinking, too.

> 
>> The strange thing is that the issues appear or disappear
>> deterministically on the binary level. This means I sometimes get a
>> U-Boot binary which runs just fine in 100% of cases. Then I change for
>> example one of the following:
>>
>> * Adding a single printf() somewhere in the boards spl.c
>> * Using the same binary but booting from SD card instead of USB loader
>> * Using the same source but switching from the OS cross compiler to the
>> one from Yocto/OE
>>
>> And afterwards I get 100% failure rate with an error as described above.
>>
>> My suspicion is that there is some memory corruption/conflict. My SPL is
>> quite large and I wonder if it exceeds some limit.
>>
>> SPL is loaded to 0x920000 and CONFIG_SPL_STACK is set to 0x960000, which
>> leaves 256 KiB in between for the SPL. But all i.MX8MP boards seem to
>> set CONFIG_SPL_MAX_SIZE=0x26000 (152 KiB) for some reason. My
>> u-boot-spl-ddr.bin currently has around 193 KiB but I don't get any
>> warning about exceeding the SPL_MAX_SIZE.
>>
>> My questions:
>>
>> * Why is CONFIG_SPL_MAX_SIZE set to 152 KiB?

I guess the remainder between the SPL code and the SPL stack is for the
DDR firmware. Which explains why I get failures with SPL exceeding 152
KiB size.

Now I also understand the reason why the power init code was implemented
using legacy non-DM drivers in other i.MX8MP boards. I probably also
need to do this to save some space.

>> * Why is there no warning in my case?

Still, I fail to see why there isn't any error or where the size check
is even implemented.

>> * Any other ideas or pointers?
>>
>> Thanks for your help!
>>
>> Best regards
>> Frieder
> 
> 
>