[PATCH] mfd: max77620: Avoid regmap mutex deadlock in power-off handler

[Diogo Ivo]

max77620_pm_power_off() is called via the sys-off framework as a
SYS_OFF_MODE_POWER_OFF handler, which runs in an atomic notifier chain
with IRQs disabled after smp_send_stop(). regmap_update_bits() acquires
the regmap mutex in this path; if another CPU held that mutex when it
was stopped, the power-off sequence deadlocks.

Replace regmap_update_bits() with i2c_smbus_write_byte_data(), which
bypasses the regmap lock entirely. The I2C core detects the atomic
context via i2c_in_atomic_xfer_mode() and uses i2c_trylock_bus() rather
than a blocking acquisition, avoiding the deadlock.

Tested on Pixel C, powers off correctly.

Assisted-by: Claude:claude-sonnet-4-6
Fixes: 744b13107d0d ("mfd: max77620: Provide system power-off functionality")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Diogo Ivo <diogo.ivo@xxxxxxxxxxxxxxxxxx>
---
This patch was tested on a local branch that sets pm_power_off =
max77620_pm_power_off() unconditionally so that the function runs.
I haven't checked whether the other bits in ONOFFCNFG1 are safe to
discard at power-off time as I don't have access to the datasheet.
If someone with access to the datasheet confirms they're not I'll
respin the patch taking that into account.
---
 drivers/mfd/max77620.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/mfd/max77620.c b/drivers/mfd/max77620.c
index 3af2974b3023..8c768968a317 100644
--- a/drivers/mfd/max77620.c
+++ b/drivers/mfd/max77620.c
@@ -487,10 +487,14 @@ static int max77620_read_es_version(struct max77620_chip *chip)
 static void max77620_pm_power_off(void)
 {
 	struct max77620_chip *chip = max77620_scratch;
+	struct i2c_client *client = to_i2c_client(chip->dev);
 
-	regmap_update_bits(chip->rmap, MAX77620_REG_ONOFFCNFG1,
-			   MAX77620_ONOFFCNFG1_SFT_RST,
-			   MAX77620_ONOFFCNFG1_SFT_RST);
+	/*
+	 * Atomic context: IRQs disabled. Use raw I2C write, bypassing
+	 * regmap locking entirely.
+	 */
+	i2c_smbus_write_byte_data(client, MAX77620_REG_ONOFFCNFG1,
+				  MAX77620_ONOFFCNFG1_SFT_RST);
 }
 
 static int max77620_probe(struct i2c_client *client)

---
base-commit: 27fa82620cbaa89a7fc11ac3057701d598813e87
change-id: 20260520-max77620_poweroff-08e39429835f

Best regards,
--  
Diogo Ivo <diogo.ivo@xxxxxxxxxxxxxxxxxx>