The IMX28 PMU (Power Management Unit) has a dedicated Linear Regulator to produce (by default) 4.2V output - available outside the chip as VDD_4P2. When system is supposed to not use VDD5V as a main power source - instead the DCDC_BATT is used; it is safe to disable this regulator. As the in-PMU DCDC switching regulator (from which DCDC_VDDA, DCDC_VDDIO and DCDC_VDDD are generated) can be driven from DCDC_BATT or output of this 4P2 regulator - by disabling the latter the use of the DCDC_BATT is forced. To be more specific - according to NXP's AN4199 the DCDC_BATT source is preferred (over VDD5V), as more efficient and stable source for industrial applications. Signed-off-by: Lukasz Majewski lukma@denx.de
Applied to u-boot-imx, master, thanks !
Best regards, Stefano Babic