RPi4 U-Boot freeze

[Stefan Agner <stefan@agner.ch>]

On 2020-09-07 16:36, Peter Robinson wrote:
>> Any thoughts on this issue?
> 
> Any reason why you're using 2020.01 and not at least 2020.07, or at
> least seeing if it's reproducible on 2020.10-rc3? The RPi4 support has
> changed quite a bit since then I suspect.
> 

Hi Peter,

It's a stable release and we support a couple of devices with the same
U-Boot version. I'd rather prefer to stay with 2020.01 for RPi4 as well.

We are on 2020.07 on development branch, and it does work fine there. So
I thought it can't be that hard, just bisect and backport whatever fixes
it... Unfortunately, it seems that there is no particular commit which
fixes it (the bisect ended up in a random unrelated commit, and it seems
that the issue appears/disappears depending on alignment/size...).

I also did applied pretty much every RPi4 related commit made after
2020.01 up until master back to 2020.01, no success either.

I fear that the problem in fact is still in master, but only appears if
certain things align a certain way... That is why I thought I bring it
up, to see if anybody else has noticed something along this lines. We do
have a rather trimmed down configuration, which might make the problem
appear more (fit in a D cache...).

I probably will just disable cached around relocation for 2020.01 and
see if it resurfaces on development branch.

--
Stefan


>> Just to be sure, I did some memory testing on the 2GB module, but no
>> issues found.
>>
>> I still somehow suspected that something else might be wrong with my
>> hardware, so I bought a new RPi4 (this time with 4GB of RAM) but the
>> very same with that:
>>
>> U-Boot 2020.01 (Aug 23 2020 - 22:02:31 +0000)
>>
>> DRAM:  3.9 GiB
>> <freeze>
>>
>> I still think there is something wrong with caching. From what I
>> understand caches are enabled by the RPi (4) firmware. Is it safe to run
>> 32-bit ARM U-Boot with enabled caches?
>>
>> --
>> Stefan
>>
>> On 2020-08-23 19:06, Stefan Agner wrote:
>> > Hi,
>> >
>> > I noticed a quite common freeze when running 32-bit U-Boot 2020.01
>> > (rpi_4_32b_defconfig) on a 2GB RPi4 model:
>> >
>> > U-Boot 2020.01 (Aug 07 2020 - 13:00:23 +0000)
>> >
>> > DRAM:  1.9 GiB
>> > <freeze, no more output>
>> >
>> > This happens fairly often, I would say 4 out of 5 boot tries. However,
>> > if it boots, everything seems to run fine.
>> >
>> > The issue seems to go away when using 2020.04 or any newer release,
>> > however, when trying to find the actual patch fixing the issue using git
>> > bisect I ended up with a MMC merge request which really seems unrelated
>> > (36bdcf7f3b). It seems that the problem is quite evasive and disappears
>> > if certain structure are aligned differently etc.
>> >
>> > Enabling initcall debugging showed that U-Boot crashes right after
>> > relocation:
>> >
>> > ...
>> > initcall: 00016f2c
>> >
>> > RAM Configuration:
>> > Bank #0: 0 948 MiB
>> > Bank #1: 40000000 1 GiB
>> > Bank #2: 0 0 Bytes
>> > Bank #3: 0 0 Bytes
>> >
>> > DRAM:  1.9 GiB
>> > initcall: 00016bb8
>> > New Stack Pointer is: 3af6d9e0
>> > initcall: 00016da4
>> > initcall: 00016ef0
>> > initcall: 00016ef8
>> > initcall: 00016d38
>> > Relocation Offset is: 3b375000
>> > Relocating to 3b37d000, new gd at 3af78ec0, sp at 3af6d9e0
>> > initcall: 00016ec8 [clear_bss]
>> > initcall: 0004465c [display_options?? only appears sometimes]
>> > <freeze>
>> >
>> > I realized when using CONFIG_SYS_(I|D)CACHE_OFF=y the problem seems to
>> > disappear. But to be 100% certain that it is cache related, I used my
>> > original configuration (which is known to "reliably" freeze), and
>> > replaced 00016ec8 with 00008688 manually in the binary, essentially
>> > swapping out function pointers in "init_sequence_f" [00008688 is
>> > cleanup_before_linux, which flushes and disables I-cache/D-cache]. And
>> > indeed, that hacked up binary does boot reliably every time:
>> >
>> > ...
>> > initcall: 00016f2c
>> >
>> > RAM Configuration:
>> > Bank #0: 0 948 MiB
>> > Bank #1: 40000000 1 GiB
>> > Bank #2: 0 0 Bytes
>> > Bank #3: 0 0 Bytes
>> >
>> > DRAM:  1.9 GiB
>> > initcall: 00016bb8
>> > New Stack Pointer is: 3af6d9e0
>> > initcall: 00016da4
>> > initcall: 00016ef0
>> > initcall: 00016ef8
>> > initcall: 00016d38
>> > Relocation Offset is: 3b375000
>> > Relocating to 3b37d000, new gd at 3af78ec0, sp at 3af6d9e0
>> > initcall: 00008688
>> > initcall: 3b38c10c
>> > initcall: 3b38c114
>> > initcall: 000172e0 (relocated to 3b38c2e0)
>> > initcall: 0001712c (relocated to 3b38c12c)
>> > ...
>> >
>> > From what I understand on RPi4 caches are enabled when entering U-Boot.
>> > I was wondering if the relocation code really can handle that?
>> >
>> > --
>> > Stefan