[U-Boot] [PATCH 7/8] power: axp209: Limit inrush current for broken boards

[Olliver Schinagl]

Some boards feature a capacitance on LDO3's output that is to large,
causing inrush currents which as a result, shut down the AXP209. This
has been reported before, without knowing the actual cause.

A fix appeared to be done with commit 0e6e34ac8db ("sunxi: Olimex A20
boards: Enable LDO3 and LDO4 regulators").

The description there is a bit misleading, the kernel does not hang
during AXP209 initialization, the PMIC shuts down, causing voltages to
drop and thus the whole system to freeze.

While the AXP209 does have the ability to ramp up the voltage slowly, to
reduce these inrush currents, the voltage rate control (VRC) however is
not applicable when switching on the LDO3 output. Only when going from
an enabled lower voltage setting, to a higher voltage setting is the VRC
in effect.

To work around this problem, we set LDO3 to the lowest possible setting
of 0.7 V if it was not yet enabled, and then let the VRC (if enabled) do
its thing. It should be noted, that for some undocumented reason, there
is a short delay needed between setting the LDO3 voltage register and
enabling the power. One would expect that this delay ought to be just
after enabling the output power at 0.7 V, but this did not work.

Signed-off-by: Olliver Schinagl <oliver at schinagl.nl>
---
 drivers/power/Kconfig  |  9 +++++++++
 drivers/power/axp209.c | 22 ++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/power/Kconfig b/drivers/power/Kconfig
index 3f10f84a89..644f206b4d 100644
--- a/drivers/power/Kconfig
+++ b/drivers/power/Kconfig
@@ -221,6 +221,15 @@ config AXP_ALDO3_VOLT_SLOPE_08
 
 endchoice
 
+config AXP_ALDO3_INRUSH_QUIRK
+	bool "axp pmic (a)ldo3 inrush quirk"
+	depends on AXP209_POWER
+	default n
+	---help---
+	The reference design denotes a value of 4.7 uF for the output capacitor
+	of LDO3. Some boards have to higher capacitance than that which causes
+	an inrush current and causes an AXP209 shutdown.
+
 config AXP_ALDO4_VOLT
 	int "axp pmic (a)ldo4 voltage"
 	depends on AXP209_POWER
diff --git a/drivers/power/axp209.c b/drivers/power/axp209.c
index 8f9269cb40..2121b88e0c 100644
--- a/drivers/power/axp209.c
+++ b/drivers/power/axp209.c
@@ -123,6 +123,28 @@ int axp_set_aldo3(unsigned int mvolt)
 	if (rc)
 		return rc;
 
+	/*
+	 * On some boards, LDO3 has a to big capacitor installed. When
+	 * turning on LDO3, this causes the AXP209 to shutdown on
+	 * voltages over 1.9 volt. As a work around, we enable LDO3
+	 * first with the lowest possible voltage. If this still causes
+	 * high inrush currents, the voltage slope should be increased.
+	 */
+#ifdef CONFIG_AXP_ALDO3_INRUSH_QUIRK
+	rc = pmic_bus_read(AXP209_OUTPUT_CTRL, &cfg);
+	if (rc)
+		return rc;
+
+	if (!(cfg & AXP209_OUTPUT_CTRL_LDO3)) {
+		rc = pmic_bus_write(AXP209_LDO3_VOLTAGE, 0x0); /* 0.7 Volt */
+		mdelay(1);
+		rc |= pmic_bus_setbits(AXP209_OUTPUT_CTRL, AXP209_OUTPUT_CTRL_LDO3);
+
+		if (rc)
+			return rc;
+	}
+#endif
+
 	if (mvolt == -1)
 		cfg = AXP209_LDO3_VOLTAGE_FROM_LDO3IN;
 	else
-- 
2.11.0