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 --- arch/arm/cpu/arm926ejs/mxs/spl_power_init.c | 3 ++- arch/arm/mach-imx/mxs/Kconfig | 7 +++++++ 2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/arm/cpu/arm926ejs/mxs/spl_power_init.c b/arch/arm/cpu/arm926ejs/mxs/spl_power_init.c index 7c584db27c..24f61b4b56 100644 --- a/arch/arm/cpu/arm926ejs/mxs/spl_power_init.c +++ b/arch/arm/cpu/arm926ejs/mxs/spl_power_init.c @@ -763,7 +763,8 @@ static void mxs_batt_boot(void) &power_regs->hw_power_5vctrl_set); }
- mxs_power_enable_4p2(); + if (CONFIG_IS_ENABLED(MXS_PMU_ENABLE_4P2_LINEAR_REGULATOR)) + mxs_power_enable_4p2(); }
/** diff --git a/arch/arm/mach-imx/mxs/Kconfig b/arch/arm/mach-imx/mxs/Kconfig index f5e45ae846..5cffc26103 100644 --- a/arch/arm/mach-imx/mxs/Kconfig +++ b/arch/arm/mach-imx/mxs/Kconfig @@ -63,6 +63,13 @@ config SPL_MXS_PMU_DISABLE_BATT_CHARGE bool "Disable Battery Charging in MX28 PMU" default n
+config SPL_MXS_PMU_ENABLE_4P2_LINEAR_REGULATOR + bool "Enable the 4P2 linear regulator in MX28 PMU" + default y + help + This option enables the 4P2 linear regulator (derived + from VDD5V) - so the VDD4P2 power source is operational. + source "board/freescale/mx28evk/Kconfig" source "board/liebherr/xea/Kconfig"