[PATCH v2] power: supply: macsmc: Support macOS 27 SMC firmware

[Janne Grunau]

On Fri, Jun 12, 2026 at 08:36:03PM +0200, Sasha Finkelstein wrote:
> The SMC firmware included in macOS 27 changed the size of BCF0 key from
> 4 to 1 bytes. This key is used for indicating that battery state is
> critically low.
> 
> Reviewed-by: Sven Peter <sven at kernel.org>
> Signed-off-by: Sasha Finkelstein <k at chaosmail.tech>

I think
Fixes: 0ebf821cf6c7 ("power: supply: Add macsmc-power driver for Apple Silicon")
and "Cc: stable" could be justified. Timing is a little unfortunate with
v7.1 expected on sunday.

> ---
> Changes in v2:
> - Addressing review feedback
> - Link to v1: https://patch.msgid.link/20260611-gate-power-v1-1-8a62721086c7@chaosmail.tech
> ---
>  drivers/power/supply/macsmc-power.c | 35 ++++++++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/power/supply/macsmc-power.c b/drivers/power/supply/macsmc-power.c
> index 33ca07460f3a..747315e372bc 100644
> --- a/drivers/power/supply/macsmc-power.c
> +++ b/drivers/power/supply/macsmc-power.c
> @@ -86,6 +86,7 @@ struct macsmc_power {
>  	bool has_ch0i; /* Force discharge (Older firmware) */
>  	bool has_ch0c; /* Inhibit charge (Older firmware) */
>  	bool has_chte; /* Inhibit charge (Modern firmware) */
> +	bool bcf0_1byte; /* Battery critical key is 1 byte (Modern firmware) */
>  
>  	u8 num_cells;
>  	int nominal_voltage_mv;
> @@ -273,6 +274,19 @@ static int macsmc_battery_get_date(const char *s, int *out)
>  	return 0;
>  }
>  
> +static int macsmc_battery_read_bcf0(struct macsmc_power *power, u32 *val)
> +{
> +	u8 tval = 0;
> +	int ret;
> +
> +	if (!power->bcf0_1byte)
> +		return apple_smc_read_u32(power->smc, SMC_KEY(BCF0), val);
> +
> +	ret = apple_smc_read_u8(power->smc, SMC_KEY(BCF0), &tval);
> +	*val = tval;
> +	return ret;
> +}

I think the following is slightly easier to read

{
	if (power->bcf0_1byte) {
		u8 tval = 0;
		int ret = apple_smc_read_u8(power->smc, SMC_KEY(BCF0), &tval);
		*val = tval;
		return ret;
	}

	return apple_smc_read_u32(power->smc, SMC_KEY(BCF0), val);
}

Not worth a respin in itself but worthwhile if there's a v3 for the the
Fixes: tag.

> +
>  static int macsmc_battery_get_capacity_level(struct macsmc_power *power)
>  {
>  	bool flag;
> @@ -280,7 +294,7 @@ static int macsmc_battery_get_capacity_level(struct macsmc_power *power)
>  	int ret;
>  
>  	/* Check for emergency shutdown condition */
> -	if (apple_smc_read_u32(power->smc, SMC_KEY(BCF0), &val) >= 0 && val)
> +	if (macsmc_battery_read_bcf0(power, &val) >= 0 && val)
>  		return POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL;
>  
>  	/* Check AC status for whether we could boot in this state */
> @@ -577,7 +591,7 @@ static void macsmc_power_critical_work(struct work_struct *wrk)
>  	 * Check if SMC flagged the battery as empty.
>  	 * We trigger a graceful shutdown to let the OS save data.
>  	 */
> -	if (apple_smc_read_u32(power->smc, SMC_KEY(BCF0), &bcf0) == 0 && bcf0 != 0) {
> +	if (macsmc_battery_read_bcf0(power, &bcf0) == 0 && bcf0 != 0) {
>  		power->orderly_shutdown_triggered = true;
>  		dev_crit(power->dev, "Battery critical (empty flag set). Triggering orderly shutdown.\n");
>  		orderly_poweroff(true);
> @@ -616,6 +630,7 @@ static int macsmc_power_probe(struct platform_device *pdev)
>  	struct device *dev = &pdev->dev;
>  	struct apple_smc *smc = dev_get_drvdata(pdev->dev.parent);
>  	struct power_supply_config psy_cfg = {};
> +	struct apple_smc_key_info info;
>  	struct macsmc_power *power;
>  	bool has_battery = false;
>  	bool has_ac_adapter = false;
> @@ -714,6 +729,20 @@ static int macsmc_power_probe(struct platform_device *pdev)
>  		if (apple_smc_key_exists(smc, SMC_KEY(CH0I)))
>  			power->has_ch0i = true;
>  
> +		ret = apple_smc_get_key_info(power->smc, SMC_KEY(BCF0), &info);
> +		if (ret) {
> +			dev_err(&pdev->dev, "Failed to determine BCF0 key size\n");
> +			return ret;
> +		}
> +		if (info.size == 1)
> +			power->bcf0_1byte = true;
> +		else if (info.size == 4)
> +			power->bcf0_1byte = false;
> +		else {
> +			dev_err(&pdev->dev, "Unexpected BCF0 key size %d\n", info.size);
> +			return -EIO;
> +		}
> +
>  		/* Reset "Optimised Battery Charging" flags to default state */
>  		if (power->has_chte)
>  			apple_smc_write_u32(smc, SMC_KEY(CHTE), 0);
> @@ -766,7 +795,7 @@ static int macsmc_power_probe(struct platform_device *pdev)
>  		power->nominal_voltage_mv = MACSMC_NOMINAL_CELL_VOLTAGE_MV * power->num_cells;
>  
>  		/* Enable critical shutdown notifications by reading status once */
> -		apple_smc_read_u32(power->smc, SMC_KEY(BCF0), &val32);
> +		macsmc_battery_read_bcf0(power, &val32);
>  
>  		psy_cfg.drv_data = power;
>  		power->batt = devm_power_supply_register(dev, &power->batt_desc, &psy_cfg);
> 
> ---

Reviewed-by: Janne Grunau <j at jannau.net>

thanks
Janne