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CCM: Changing clock parent freezes system

Question asked by Wolfgang Bär on Feb 26, 2019
Latest reply on Mar 4, 2019 by igorpadykov


we have an imx8md processor on a custom board and we need to use CLK_EXT3 as input to one of the SAI modules.

However if we change the assigned parent in the device tree the board freezes without any error during boot up:


&sai2 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_sai2>;
assigned-clocks = <&clk IMX8MQ_CLK_SAI2>;
assigned-clock-parents = <&clk IMX8MQ_CLK_EXT3>;
status = "okay";

If I change the clock parent to any other (e.g. 25M_REF_CLK or IMX8MQ_AUDIO_PLL1_OUT) of the supported clock parents according to reference manual it works. 


The pins are configured as required:


pinctrl_hog: hoggrp {
fsl,pins = <


The same applies to clock slice 117 IPP_DO_CLKO2 if I try to reparent to anything other than the default 25M_REF_CLK. The system instantly freezes without any error.


If I change the above from userspace via the CCM registers the same happens -> freeze:

Set CLKO2 to 32K reference clock: devmem2 0x3038BA84 w 0x17000000


The reference manual does not mention anything regarding these topics or if there is a special sequence etc.

which must be followed to change parents. 


Any help or hints are appreciated!