arm: mxs: Provide Kconfig option to to not use VDD5V as IMX28 PMU source

This option sets the current limit for 5V source to zero, so all
the PMU outputs are primarily powered from battery source (DCDC_BAT).

This option may be set on systems, where the 5V is NOT supposed to be
in any scenario powering the system - for example on systems where
DCDC_BAT is connected to fixed and regulated 4.2V source (so the
"battery" is not present).

Signed-off-by: Lukasz Majewski <lukma@denx.de>

arch/arm/cpu/arm926ejs/mxs/spl_power_init.c

@@ -752,6 +752,10 @@ static void mxs_batt_boot(void)
 		POWER_5VCTRL_CHARGE_4P2_ILIMIT_MASK,
 		0x8 << POWER_5VCTRL_CHARGE_4P2_ILIMIT_OFFSET);
 
+	if (CONFIG_IS_ENABLED(MXS_PMU_MINIMAL_VDD5V_CURRENT))
+		setbits_le32(&power_regs->hw_power_5vctrl,
+			     POWER_5VCTRL_ILIMIT_EQ_ZERO);
+
 	mxs_power_enable_4p2();
 }
 

arch/arm/mach-imx/mxs/Kconfig

@@ -51,6 +51,14 @@ endchoice
 config SYS_SOC
 	default "mxs"
 
+config SPL_MXS_PMU_MINIMAL_VDD5V_CURRENT
+	bool "Force minimal current draw from VDD5V by MX28 PMU"
+	default n
+	help
+	  After setting this option, the current drawn from VDD5V
+	  by the PMU is reduced to zero - the DCDC_BATT is used as
+	  the main power source for PMU.
+
 source "board/freescale/mx28evk/Kconfig"
 source "board/liebherr/xea/Kconfig"