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i.MX6Q: Downgrade ARM speed to 400Mhz before ldo bypassed

Question asked by Nori Shinozaki on May 22, 2016
Latest reply on May 26, 2016 by Nori Shinozaki

Hello Champs,


I found this comment in u-boot 2014-04 arch/arm/cpu/armv7/mx6/soc.c

void prep_anatop_bypass(void)


    struct mxc_ccm_reg *mxc_ccm = (struct mxc_ccm_reg *)CCM_BASE_ADDR;


    arm_orig_podf = readl(&mxc_ccm->cacrr);


    * Downgrade ARM speed to 400Mhz as half of boot 800Mhz before ldo

     * bypassed, also downgrade internal vddarm ldo to 0.975V.

     * VDDARM_IN 0.975V + 125mV = 1.1V < Max(1.3V)

     * otherwise at 800Mhz(i.mx6dl):

     * VDDARM_IN 1.175V + 125mV = 1.3V = Max(1.3V)

     * We need provide enough gap in this case.


Why do we need to downgrade to 400MHz?