[PATCH v3] mfd: tps65910: Correct power-off programming sequence

[Dmitry Osipenko <digetx@gmail.com>]

This patch fixes system shutdown on a devices that use TPS65910 as a
system's power controller. In accordance to the TPS65910 datasheet, the
PMIC's state-machine transitions into the OFF state only when DEV_OFF
bit of DEVCTRL_REG is set. The ON / SLEEP states also should be cleared,
otherwise PMIC won't get into a proper state on shutdown. Devices like
Nexus 7 tablet and Ouya game console are now shutting down properly.

Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Zack Pearsall <zpearsall@yahoo.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---

Changelog:

v3: - Removed the DEV_SLP_MASK clearing and adding clarifying comment to
      the code about why clearing PWR_OFF bit needs to be done, which was
      suggested by  Michał Mirosław in a review comment to v2.

    - Added tested-by from Peter Geis who tested v3 on his Ouya game
      console.

v2: - Now using a single tps65910_reg_update_bits() instead of set+clear.
      Thanks to Michał Mirosław for the suggestion.

 drivers/mfd/tps65910.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/tps65910.c b/drivers/mfd/tps65910.c
index 11959021b50a..388214241558 100644
--- a/drivers/mfd/tps65910.c
+++ b/drivers/mfd/tps65910.c
@@ -436,12 +436,18 @@ static void tps65910_power_off(void)
 
 	tps65910 = dev_get_drvdata(&tps65910_i2c_client->dev);
 
+	/*
+	 * Note that the PWR_OFF bit needs to be set separately, before
+	 * transitioning to the OFF state. It enables the "sequential"
+	 * power-off mode on TPS65911, it's a NO-OP on TPS65910.
+	 */
 	if (tps65910_reg_set_bits(tps65910, TPS65910_DEVCTRL,
 			DEVCTRL_PWR_OFF_MASK) < 0)
 		return;
 
-	tps65910_reg_clear_bits(tps65910, TPS65910_DEVCTRL,
-			DEVCTRL_DEV_ON_MASK);
+	tps65910_reg_update_bits(tps65910, TPS65910_DEVCTRL,
+				 DEVCTRL_DEV_OFF_MASK | DEVCTRL_DEV_ON_MASK,
+				 DEVCTRL_DEV_OFF_MASK);
 }
 
 static int tps65910_i2c_probe(struct i2c_client *i2c,
-- 
2.27.0