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

[Frieder Schrempf]

On 15.03.23 15:42, Frieder Schrempf wrote:
> 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.

Still, it doesn't really make sense to me at the moment as the
u-boot-spl-ddr.bin already contains the DDR firmware it should be fine
to exceed the 152 KiB size. My u-boot-spl.bin (without DDR firmware) is
only 135 KiB.

Sorry for spamming you by thinking out loud... ;)

> 
> 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