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

> > 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.

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.

> 
> 
> > 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...
> > 
> > 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.

> PMIC comes to my mind. Does it need some configuration?

The PMIC has the same register/value writes as in the u-boot version.

> 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).

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

Cheers
Marc