I am getting this stack trace when booting Linux after starting m4 from U-Boot:
[ 0.055186] ------------[ cut here ]------------
[ 0.055230] WARNING: CPU: 0 PID: 1 at arch/arm/mach-imx/pm-imx7.c:1156 imx7d_pm_init+0xa4/0x464
[ 0.055253] Modules linked in:
[ 0.055274] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.91-5.2.0-devel+git.6afb048a71e3 #1
[ 0.055296] Hardware name: Freescale i.MX7 Dual (Device Tree)
[ 0.055336] [<8010dadc>] (unwind_backtrace) from [<8010ae00>] (show_stack+0x10/0x14)
[ 0.055369] [<8010ae00>] (show_stack) from [<80928a58>] (dump_stack+0x90/0xa4)
[ 0.055401] [<80928a58>] (dump_stack) from [<8091f618>] (__warn+0xbc/0xd8)
[ 0.055426] [<8091f618>] (__warn) from [<8091f684>] (warn_slowpath_fmt+0x50/0x98)
[ 0.055455] [<8091f684>] (warn_slowpath_fmt) from [<80d096c0>] (imx7d_pm_init+0xa4/0x464)
[ 0.055487] [<80d096c0>] (imx7d_pm_init) from [<80d08ec8>] (imx7d_init_machine+0x38/0x228)
[ 0.055518] [<80d08ec8>] (imx7d_init_machine) from [<80d028a4>] (customize_machine+0x20/0x30)
[ 0.055549] [<80d028a4>] (customize_machine) from [<8010264c>] (do_one_initcall+0x44/0x194)
[ 0.055582] [<8010264c>] (do_one_initcall) from [<80d00e3c>] (kernel_init_freeable+0x138/0x1d4)
[ 0.055615] [<80d00e3c>] (kernel_init_freeable) from [<80928c00>] (kernel_init+0x8/0x110)
[ 0.055645] [<80928c00>] (kernel_init) from [<801010e8>] (ret_from_fork+0x14/0x2c)
[ 0.055668] Exception stack(0xac093fb0 to 0xac093ff8)
[ 0.055688] 3fa0: 00000000 00000000 00000000 00000000
[ 0.055715] 3fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 0.055742] 3fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[ 0.055768] ---[ end trace d83f4bdb01ebbe1d ]---
[ 0.056026] imx7d_enet_clk_sel: fec1: failed to get enet_out clock, assuming ext. clock source