Troubles booting kernel with new imx8 board

[Ahmad Fatoum]

Hello Marc,

On 27.05.23 07:35, marc at cpdesign.com.au wrote:
> Hi,
> 
> Thanks for responses, some more info:
> - imx8mp based system, 1Gb LPDDR, uses same PMIC as other boards (PCA9450)
> - barebox master
> - u-boot is NXP fork
> - kernel is NXP fork, 5.15.31

Keep in mind that, as far as I am aware, most testing, if not all,
of the barebox i.MX8MP support was against the mainline kernel. Certainly
all projects at our side don't use NXP's fork.

>>> I'm trying to get barebox going for a new imx8mp based board. I can
>>> successfully power on and get to a barebox prompt etc and fiddle with
>>> gpios, files on sd, memtest etc, but when booting to kernel it will hang.
>>> Note though that the board boots ok with u-boot (using exact same kernel
>>> image).
>> Do you have an example crash dump? Does the kernel crash reproducibly or
>> randomly?
> 
> It always hangs at the same point in the kernel boot sequence (see "startup-
> log-barebox.txt"). You can also see "startup-log-u-boot.txt" for the output of 
> a complete boot.

My go-to for hanging boot is

  no_console_suspend pm_debug_messages pd_ignore_unused clk_ignore_unused

Maybe add maxcpus=1 and see if you get some useful indication what happens
just before hang?

> If i change some kernel config options the boot progresses further, and when 
> CONFIG_ARM_IMX_CPUFREQ_DT=n and CONFIG_IMX_SDMA=n then it will get to systemd 
> starting.

Maybe one of these drivers calls in TF-A? Do you use same TF-A/ATF in both
configurations?

>>> I'm trying to figure out what is different between booting via uboot and
>>> barebox, I'm new to imx8 so have been going down a few rabbit holes...

FWIW, here's a FOSDEM talk on how barebox boots the i.MX8M:
https://archive.fosdem.org/2021/schedule/event/from_reset_vector_to_kernel/

>>> Disabling various drivers (eg imx-cpufreq-dt) in the kernel will get past
>>> the hang, but result in a crash later on in the boot sequence. Disabling
>>> that may get further but will result in a crash somewhere else.
>>> My instinct is that its something to do with sdma, but a lot of this is
>>> still a black box to me.
>>
>> SDMA is only used in few devices like UART, I2C, SPI and sound. Apart from
>> sound all devices should work without SDMA, so you could disable the
>> driver.
> 
> I was getting (after disabling some things in kernel) crash traces in 
> sdma_transfer_init etc, which is what made me suspect it. (see startup-log-
> barebox-after-kernel-change1.txt)
> Disabling the driver does indeed avoid this crash.

Hmm, strange.

> 
>> PMIC comes to my mind. Does it need some configuration?
> 
> The PMIC has the same register/value writes as in the u-boot version.

Are you sure there are no writes in main U-Boot apart from what SPL sets up?

>> Is the amount of memory detected correctly by barebox?
> 
> Barebox detects 1Gb, correct
> 
> I did a compare of the startup logs (The cuts are to remove the timestamps)
> ```kompare <(diff <(cut -c 15- startup-log-u-boot.txt) <(cut -c 15- startup-
> log-barebox.txt))```
> 
> I noticed some differences in the 'reserved mem' at the start and the 'NUMA' 
> early memory node ranges.
> 
> When booting from u-boot I get:
>     [    0.000000] Reserved memory: created CMA memory pool at 
> 0x0000000060000000, size 512 MiB
>     [    0.000000] OF: reserved mem: initialized node linux,cma, compatible id 
> shared-dma-pool
> 
> But when booting from barebox:
>      [    0.000000] OF: reserved mem: failed to allocate memory for node 
> 'linux,cma'
>     [    0.000000] Reserved memory: created DMA memory pool at 
> 0x0000000055400000, size 1 MiB
> 
> 
> For the early node ranges:
> from u-boot:
> 
> [    0.000000] NUMA: NODE_DATA [mem 0x5fdba800-0x5fdbcfff]
> [    0.000000] Zone ranges:
> [    0.000000]   DMA      [mem 0x0000000040000000-0x000000007fffffff]
> [    0.000000]   DMA32    empty
> [    0.000000]   Normal   empty
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000040000000-0x0000000054ffffff]
> [    0.000000]   node   0: [mem 0x0000000055000000-0x000000005500ffff]
> [    0.000000]   node   0: [mem 0x0000000055010000-0x00000000550fefff]
> [    0.000000]   node   0: [mem 0x00000000550ff000-0x00000000550fffff]
> [    0.000000]   node   0: [mem 0x0000000055100000-0x00000000553fffff]
> [    0.000000]   node   0: [mem 0x0000000055400000-0x00000000554fffff]
> [    0.000000]   node   0: [mem 0x0000000055500000-0x0000000055ffffff]
> [    0.000000]   node   0: [mem 0x0000000058000000-0x000000007fffffff]
> 
> 
> and from barebox:
> 
> [    0.000000] NUMA: NODE_DATA [mem 0x7fdaa800-0x7fdacfff]
> [    0.000000] Zone ranges:
> [    0.000000]   DMA      [mem 0x0000000040000000-0x000000007fffffff]
> [    0.000000]   DMA32    empty
> [    0.000000]   Normal   empty
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000040000000-0x0000000054ffffff]
> [    0.000000]   node   0: [mem 0x0000000055000000-0x000000005500ffff]
> [    0.000000]   node   0: [mem 0x0000000055010000-0x00000000550fefff]
> [    0.000000]   node   0: [mem 0x00000000550ff000-0x00000000550fffff]
> [    0.000000]   node   0: [mem 0x0000000055100000-0x00000000553fffff]
> [    0.000000]   node   0: [mem 0x0000000055400000-0x00000000554fffff]
> [    0.000000]   node   0: [mem 0x0000000055500000-0x000000007fffffff]
> 
> Notably there is an range in the u-boot ranges which creates a gap from 
> 0x56000000 to 0x57ffffff (32Mb).

That's probably OP-TEE. That would be in line with startup-log-u-boot saying:

  [    1.636240] optee: revision 3.19 (00919403)

Whether that's a problem depends on where OP-TEE comes from. On i.MX8MQ, OP-TEE
was built into TF-A. On i.MX8MM, it was usually outside. If it's built into
TF-A in your i.MX8MP setup, this would explain your problems.


> I'm wondering how this difference comes about when both bootloaders are 
> booting the same devicetree and kernel image?

The devicetrees are not the same, because of bootloader fixups:

  - U-Boot inserts OP-TEE nodes for you. barebox can too, but you don't have
    that configured (not sure if you need it)

  - NXP U-Boot messes with power domains, e.g. disable specific VPU nodes _by
    name_ for stripped down versions of i.MX8MP. barebox also does disabling,
    but on the upstream device tree nodes.

If you want an accurate comparison of the device trees, look in /proc/devicetree
and compare. dtc can make a dts out of the directory. If it's too flaky with
barebox, add some -v to boot/bootm (I think -vv should suffice) and barebox
will print the fixed up device tree to console before bootup.


What seems likely is that OP-TEE is built into the TF-A and you fail
to account for that. If so, try building TF-A yourself without OP-TEE and see
if it's better. The barebox docs for i.MX8MP-EVK have instructions.

If it is better and you want OP-TEE, have OP-TEE external to TF-A.
This is better anyway, because TF-A+OP-TEE+barebox PBL may get too big in
SRAM in future.

Let me know how it goes.

Cheers,
Ahmad


> 
> Cheers
> Marc
> 
> 
> 

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