Boot is delayed 30 seconds on cold boot imx8

[Amelius]

Hey,

I'm experiencing a strange behavior during a cold start up (the device is disconnected from power longer than 2 Minutes and than powered up). The boot up is delayed right after "ddrc freq set to low bus mode" by 30s twice (see log) and the total boot time is around 80s.

If the device is rebooted or just unplugged and plugged for less than 20 seconds, the boot time is around 15s

Processor: i.MX 8M

Greetings

[Zhiming_Liu]

@Amelius 

Does this issue exist on customer board?

[Amelius]

Yes, it's a customer board

[Zhiming_Liu]

Try to redo ddr test.This issue relates to ddr hardware design. 

https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/i-MX-8M-Family-DDR-Tool-Release/ta-p/110...

[Amelius]

After further investigation I came to the conclusion that the behavior occurs after adding the RT kernel patch patch-5.4.3-rt1 and the kernel config options CONFIG_EMBEDDED=y and CONFIG_PREEMPT_RT=y

adding 
CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
CONFIG_DEVFREQ_GOV_PERFORMANCE=y
didn't bring an improvement

it doesn't look like it has to do with the ddr hardware design since the manufacture did extensiv tests with the mentioned tool

Index of /pub/linux/kernel/projects/rt/5.4/older/