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

[Dmitry Osipenko]

20.05.2026 17:28, Diogo Ivo пишет:
> 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>

Kernel parks secondary CPUs before powering off system, hence there
shouldn't be a locking contention.

Have you checked whether regmap_write_bits() works?