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SoC lock-up when trying to CCM_UpdateRoot for I2C1 from M4 after Linux boots

Question asked by D. RY on Oct 4, 2018
Latest reply on Oct 19, 2018 by Yuri Muhin

I got the problem that when my M4 code using I2C1 is started after Linux boots, then the M4 and then A7 or entire SoC seems gets hard locked on when trying to set clocks for the I2C1 on the M4. The same code works ok if booted just from U-boot, with no Linux.


The M4 init code for I2C1 is : (BOARD_I2C_xx refers to I2C1 stuff)


RDC_SetPdapAccess(RDC, BOARD_I2C_RDC_PDAP, 3 << (BOARD_DOMAIN_ID * 2), false, false);
/* Select I2C clock derived from OSC clock(24M) */
CCM_UpdateRoot(CCM, BOARD_I2C_CCM_ROOT, ccmRootmuxI2cOsc24m, 0, 0);  <---- Locks up here when updating register
/* Enable I2C clock */
CCM_ControlGate(CCM, BOARD_I2C_CCM_CCGR, ccmClockNeededRunWait);
/// rest ....


The lock-up is on line with CCM_UpdateRoot, when that function trying to write to CCM_REG(ccmRoot) .


In the Linux sources I traced that a conflict is created in clk-imx7d.c , with:

imx_clk_set_parent(clks[IMX7D_SIM1_ROOT_SRC], clks[IMX7D_PLL_SYS_MAIN_120M_CLK]);


I haven't fully traced into that call, but if I remove this parent setting, then my problem with I2C1 init on the M4 goes away .. 


Any help / suggestions .. ? How does SIM1 root clock update mess up updating I2C1 root clock ?