colibri_t20: disable PMIC sleep mode on low supply voltage

The Colibri T20's PMIC enters a sleep mode on low supply voltage < 3.0V
±2.5% (2.92...3.08V). Rising the main supply voltage again does not
bring it back to regular operation. Not even a full reset does bring
the module back. A full power cycle was required to reboot the system.
A long positive pulse on the PMICs resume pin also reboots the system
but this pin is only accessible as a test point on the module.

This patch configures the PMIC through I2C to not enter this sleep mode
plus force it to normal state upon sleep request exit should this ever
happen.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>

board/toradex/colibri_t20/colibri_t20.c

@@ -13,9 +13,44 @@
 #include <asm/arch-tegra/tegra.h>
 #include <asm/gpio.h>
 #include <asm/io.h>
+#include <i2c.h>
+
+#define PMU_I2C_ADDRESS		0x34
+#define MAX_I2C_RETRY		3
+#define PMU_SUPPLYENE		0x14
+#define PMU_SUPPLYENE_SYSINEN	(1<<5)
+#define PMU_SUPPLYENE_EXITSLREQ	(1<<1)
 
 int arch_misc_init(void)
 {
+	/* Disable PMIC sleep mode on low supply voltage */
+	struct udevice *dev;
+	u8 addr, data[1];
+	int err;
+
+	err = i2c_get_chip_for_busnum(0, PMU_I2C_ADDRESS, 1, &dev);
+	if (err) {
+		debug("%s: Cannot find PMIC I2C chip\n", __func__);
+		return err;
+	}
+
+	addr = PMU_SUPPLYENE;
+
+	err = dm_i2c_read(dev, addr, data, 1);
+	if (err) {
+		debug("failed to get PMU_SUPPLYENE\n");
+		return err;
+	}
+
+	data[0] &= ~PMU_SUPPLYENE_SYSINEN;
+	data[0] |= PMU_SUPPLYENE_EXITSLREQ;
+
+	err = dm_i2c_write(dev, addr, data, 1);
+	if (err) {
+		debug("failed to set PMU_SUPPLYENE\n");
+		return err;
+	}
+
 	if (readl(NV_PA_BASE_SRAM + NVBOOTINFOTABLE_BOOTTYPE) ==
 	    NVBOOTTYPE_RECOVERY)
 		printf("USB recovery mode\n");