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

[Joshua Peisach]

On Thu Jun 11, 2026 at 12:49 PM EDT, 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.
>
> Signed-off-by: Sasha Finkelstein <k at chaosmail.tech>
> ---
>  drivers/power/supply/macsmc-power.c | 34 +++++++++++++++++++++++++++++++---
>  1 file changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/power/supply/macsmc-power.c b/drivers/power/supply/macsmc-power.c
> index 33ca07460f3a..650dc8740f71 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 */
>  
>  	u8 num_cells;
>  	int nominal_voltage_mv;
> @@ -273,6 +274,18 @@ 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;
> +	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);

Would I be ridiculous to suggest adding a newline after the return
statement?

> +	*val = tval;
> +	return ret;
> +}
> +
>  static int macsmc_battery_get_capacity_level(struct macsmc_power *power)
>  {
>  	bool flag;
> @@ -280,7 +293,7 @@ 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 +590,7 @@ 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 +629,7 @@ 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;