---
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;
+}

+
 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);

---