cpu hangs randomly but can't be reset by watchdog

[feifeihu]

We are running Android 4.4.3 with kernel3.10.53 in imx6dl，recently we meet strange cpu hang issue, it happens suddenly after clicking something , kernel is irresponsible at all,even sysrq has no effect, and the screen is blank,seems no video output from CPU,but the watchdog seems does not work, the CPU never be reset unless we cut down the power.

Can anyone help explain why CPU won't be reset in this case? How can we find out the root cause of hanging?

Thanks!

[igorpadykov · Accepted solution]

Hi Feifei

please check power supplies using recommendations in Hardware User Guide

https://www.nxp.com/docs/en/user-guide/IMX6DQ6SDLHDG.pdf 

also may be recommended to run ddr tester and rebuild image (change uboot/board/freescale/mx6sabresd/mx6dlsabresd.cfg) with new calibration coefficients found from test

i.MX6/7 DDR Stress Test Tool V2.70 

Best regards
igor
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[feifeihu]

Hi,igorpadykov ,

Thanks, The root cause is found that there is something affect PMIC via I2C, then the PMIC powered down some pin.