Boot freezes in iMX6 with no error messages

[carolcabral]

Hello everyone,

I'm working with a CM-FX6 board that currently runs kernel 3.0.35. I'd like to upgrade it, but the image in CM-FX6_LinuxPackage-4.1.15 is missing some drivers I'd like to include in my build.

So I got the kernel source code and applied the patches from CM-FX6_LinuxPackage-4.1.15 folder. I used the linux-4.1.15-cm-fx6-8.0.config to make a new zImage, but I'm unable to boot it on the board, it just freezes after ALSA device list. I added 'debug initcall_debug' options in command line, and the output hangs in:

ALSA device list:
#0: cm-fx6
initcall alsa_sound_last_init+0x0/0x70 returned 0 after 0 usecs

No error messages, nothing. I'm using the same rootfs in CM-FX6_LinuxPackage-4.1.15 and the same U-boot environment and dtb file that I can sucessfully boot. Is there anyway I can debug this any further? It seems to me U-boot is not loading the next stage, because the image that works proceeds from here to mounting the filesystem:

ALSA device list:
#0: cm-fx6
#1: imx-hdmi-soc
#2: imx-spdif
initcall alsa_sound_last_init+0x0/0x6c returned 0 after 6027 usecs
EXT4-fs (mmcblk2p2): mounted filesystem with ordered data mode. Opts: (null)
VFS: Mounted root (ext4 filesystem) on device 179:2.
devtmpfs: mounted
Freeing unused kernel memory: 340K (80a3f000 - 80a94000)
systemd[1]: System time before build time, advancing clock.

But I'm also intrigued by the difference in alsa_sound_last_init return time, can the other soundcards (imx-hdmi-soc and imx-spdif) be blocking the process? 

I've already tried removing 'rootwait' from U-boot command line and removing CONFIG_CPU_IDLE as per https://community.nxp.com/t5/i-MX-Processors/imx6sx-kernel-hangs-at-rootfs-mount/td-p/964920. I've also tried removing ALSA support, but the boot hangs in another step and I need audio support anyways...