asmc: add MMIO backend for T2 Macs

T2 Macs (2018+) expose the SMC via memory-mapped registers instead of
I/O ports. Add asmcmmio.c/asmcmmio.h implementing the MMIO transport:
key read/write, getinfo, getbyindex, and a poll-based wait with
exponential backoff.

The driver probes for MMIO at attach time by checking the LDKN firmware
version key; if MMIO is available it is used, otherwise the standard
I/O port backend is used.

T2 fan speeds use IEEE 754 floats instead of fpe2 fixed-point.
Per-fan manual mode uses F%dMd keys instead of the FS! bitmask.
Battery charge limit is exposed via dev.asmc.N.battery_charge_limit.

Tested on:
  MacBookPro16,2 (A2251, iBridge2,10)
  MacBookPro15,4 (A2159, iBridge2,8)
  MacBookAir8,2  (A1932, iBridge2,5)
  Mac mini 8,1   (A1993, iBridge2,7)
  iMac20,2       (A2115, iBridge2,16)
  iMacPro1,1     (A1862, iBridge1,1)

MFC after:	2 weeks
Reviewed by:	ngie, adrian
Differential Revision:	https://reviews.freebsd.org/D57086

sys/conf/files.amd64

@@ -113,6 +113,7 @@ crypto/openssl/amd64/ossl_aes_gcm_avx512.c	optional ossl
 crypto/openssl/ossl_aes_gcm.c	optional ossl
 dev/amdgpio/amdgpio.c		optional	amdgpio
 dev/asmc/asmc.c			optional	asmc isa
+dev/asmc/asmcmmio.c		optional	asmc isa
 dev/axgbe/if_axgbe_pci.c	optional	axp
 dev/axgbe/xgbe-desc.c		optional	axp
 dev/axgbe/xgbe-dev.c		optional	axp

sys/dev/asmc/asmc.c

@@ -57,6 +57,7 @@
 
 #include <dev/acpica/acpivar.h>
 #include <dev/asmc/asmcvar.h>
+#include <dev/asmc/asmcmmio.h>
 
 #include <dev/backlight/backlight.h>
 #include "backlight_if.h"
@@ -426,17 +427,40 @@ asmc_attach(device_t dev)
 	struct sysctl_ctx_list *sysctlctx;
 	struct sysctl_oid *sysctlnode;
 
-	sc->sc_ioport = bus_alloc_resource_any(dev, SYS_RES_IOPORT,
-	    &sc->sc_rid_port, RF_ACTIVE);
-	if (sc->sc_ioport == NULL) {
-		device_printf(dev, "unable to allocate IO port\n");
-		return (ENOMEM);
+	/*
+	 * Try MMIO first (T2 Macs expose SMC via memory-mapped I/O).
+	 * Fall back to standard I/O port if MMIO is not available.
+	 */
+	sc->sc_rid_mem = 0;
+	sc->sc_iomem = bus_alloc_resource_any(dev, SYS_RES_MEMORY,
+	    &sc->sc_rid_mem, RF_ACTIVE);
+	if (sc->sc_iomem != NULL) {
+		if (asmc_mmio_probe(dev) == 0) {
+			sc->sc_is_mmio = 1;
+			device_printf(dev, "using MMIO backend (T2)\n");
+		} else {
+			bus_release_resource(dev, SYS_RES_MEMORY,
+			    sc->sc_rid_mem, sc->sc_iomem);
+			sc->sc_iomem = NULL;
+		}
+	}
+
+	if (!sc->sc_is_mmio) {
+		sc->sc_ioport = bus_alloc_resource_any(dev, SYS_RES_IOPORT,
+		    &sc->sc_rid_port, RF_ACTIVE);
+		if (sc->sc_ioport == NULL) {
+			device_printf(dev, "unable to allocate IO port\n");
+			ret = ENOMEM;
+			goto err;
+		}
 	}
 
 	sysctlctx = device_get_sysctl_ctx(dev);
 	sysctlnode = device_get_sysctl_tree(dev);
 
-	mtx_init(&sc->sc_mtx, "asmc", NULL, MTX_SPIN);
+	/* Mutex may already be initialized by asmc_mmio_probe() */
+	if (!mtx_initialized(&sc->sc_mtx))
+		mtx_init(&sc->sc_mtx, "asmc", NULL, MTX_SPIN);
 
 	/* Read SMC revision, key count, fan count */
 	ret = asmc_init(dev);
@@ -615,6 +639,18 @@ asmc_attach(device_t dev)
 	    "SMC key type (4 chars)");
 #endif
 
+	/*
+	 * Battery charge limit (T2 Macs).
+	 */
+	if (sc->sc_is_t2 &&
+	    asmc_key_getinfo(dev, ASMC_KEY_BCLM, NULL, NULL) == 0) {
+		SYSCTL_ADD_PROC(sysctlctx,
+		    SYSCTL_CHILDREN(sysctlnode), OID_AUTO, "battery_charge_limit",
+		    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
+		    dev, 0, asmc_bclm_sysctl, "I",
+		    "Battery charge limit (0-100)");
+	}
+
 	if (!sc->sc_has_sms)
 		goto nosms;
 
@@ -736,6 +772,7 @@ asmc_detach(device_t dev)
 		    sc->sc_ioport);
 		sc->sc_ioport = NULL;
 	}
+	asmc_mmio_detach(dev, sc);
 	if (mtx_initialized(&sc->sc_mtx)) {
 		mtx_destroy(&sc->sc_mtx);
 	}
@@ -788,10 +825,25 @@ asmc_init(device_t dev)
 	sysctlctx = device_get_sysctl_ctx(dev);
 
 	error = asmc_key_read(dev, ASMC_KEY_REV, buf, 6);
-	if (error != 0)
-		goto out;
-	device_printf(dev, "SMC revision: %x.%x%x%x\n", buf[0], buf[1], buf[2],
-	    ntohs(*(uint16_t *)buf + 4));
+	if (error != 0) {
+		/*
+		 * Could not read REV key; T2 Macs may not have it.
+		 * Use #KEY as a liveness check instead.
+		 */
+		if (sc->sc_is_t2) {
+			error = asmc_key_read(dev, ASMC_NKEYS, buf, 4);
+			if (error != 0)
+				goto out;
+			device_printf(dev, "T2 SMC: %d keys\n",
+			    be32dec(buf));
+		} else {
+			goto out;
+		}
+	} else {
+		device_printf(dev, "SMC revision: %x.%x%x%x\n",
+		    buf[0], buf[1], buf[2],
+		    ntohs(*(uint16_t *)buf + 4));
+	}
 
 	/* Auto power-on after AC power loss (AUPO). */
 	if (asmc_key_read(dev, ASMC_KEY_AUPO, buf, 1) == 0) {
@@ -1041,8 +1093,11 @@ asmc_command(device_t dev, uint8_t command)
 static int
 asmc_key_read(device_t dev, const char *key, uint8_t *buf, uint8_t len)
 {
-	int i, error = 1, try = 0;
 	struct asmc_softc *sc = device_get_softc(dev);
+	int i, error = 1, try = 0;
+
+	if (sc->sc_is_mmio)
+		return (asmc_mmio_key_read(dev, key, buf, len));
 
 	mtx_lock_spin(&sc->sc_mtx);
 
@@ -1180,6 +1235,9 @@ asmc_key_getinfo(device_t dev, const char *key, uint8_t *len, char *type)
 	uint8_t info[ASMC_KEYINFO_RESPLEN];
 	int i, error = -1, try = 0;
 
+	if (sc->sc_is_mmio)
+		return (asmc_mmio_key_getinfo(dev, key, len, type));
+
 	mtx_lock_spin(&sc->sc_mtx);
 
 begin:
@@ -1715,6 +1773,14 @@ asmc_key_dump_by_index(device_t dev, int index, char *key_out,
 	int error = ENXIO, try = 0;
 	int i;
 
+	if (sc->sc_is_mmio) {
+		error = asmc_mmio_key_getbyindex(dev, index, key_out);
+		if (error != 0)
+			return (error);
+		return (asmc_mmio_key_getinfo(dev, key_out, len_out,
+		    type_out));
+	}
+
 	mtx_lock_spin(&sc->sc_mtx);
 
 	index_buf[0] = (index >> 24) & 0xff;
@@ -1808,8 +1874,11 @@ asmc_key_search(device_t dev, const char *prefix, unsigned int *idx)
 static int
 asmc_key_write(device_t dev, const char *key, uint8_t *buf, uint8_t len)
 {
-	int i, error = -1, try = 0;
 	struct asmc_softc *sc = device_get_softc(dev);
+	int i, error = -1, try = 0;
+
+	if (sc->sc_is_mmio)
+		return (asmc_mmio_key_write(dev, key, buf, len));
 
 	mtx_lock_spin(&sc->sc_mtx);
 
@@ -1865,14 +1934,30 @@ asmc_fan_count(device_t dev)
 static int
 asmc_fan_getvalue(device_t dev, const char *key, int fan)
 {
+	struct asmc_softc *sc = device_get_softc(dev);
 	int speed;
-	uint8_t buf[2];
+	uint8_t buf[4];
 	char fankey[5];
+	char type[ASMC_TYPELEN + 1];
 
 	snprintf(fankey, sizeof(fankey), key, fan);
-	if (asmc_key_read(dev, fankey, buf, sizeof(buf)) != 0)
-		return (-1);
-	speed = (buf[0] << 6) | (buf[1] >> 2);
+
+	/*
+	 * T2 Macs use IEEE 754 float ("flt ") for fan speeds,
+	 * stored little-endian in the MMIO data register.
+	 * Standard Macs use s14.2 fixed-point ("fpe2", 2 bytes).
+	 */
+	if (sc->sc_is_t2 &&
+	    asmc_key_getinfo(dev, fankey, NULL, type) == 0 &&
+	    strncmp(type, "flt ", 4) == 0) {
+		if (asmc_key_read(dev, fankey, buf, 4) != 0)
+			return (-1);
+		speed = (int)asmc_float_to_u32(le32dec(buf));
+	} else {
+		if (asmc_key_read(dev, fankey, buf, 2) != 0)
+			return (-1);
+		speed = (buf[0] << 6) | (buf[1] >> 2);
+	}
 
 	return (speed);
 }
@@ -1895,17 +1980,30 @@ asmc_fan_getstring(device_t dev, const char *key, int fan, uint8_t *buf,
 static int
 asmc_fan_setvalue(device_t dev, const char *key, int fan, int speed)
 {
-	uint8_t buf[2];
+	struct asmc_softc *sc = device_get_softc(dev);
+	uint8_t buf[4];
 	char fankey[5];
-
-	speed *= 4;
-
-	buf[0] = speed >> 8;
-	buf[1] = speed;
+	char type[ASMC_TYPELEN + 1];
 
 	snprintf(fankey, sizeof(fankey), key, fan);
-	if (asmc_key_write(dev, fankey, buf, sizeof(buf)) < 0)
-		return (-1);
+
+	if (sc->sc_is_t2 &&
+	    asmc_key_getinfo(dev, fankey, NULL, type) == 0 &&
+	    strncmp(type, "flt ", 4) == 0) {
+		uint32_t fval;
+		speed = MAX(speed, 0);
+		speed = MIN(speed, 65535);
+		fval = asmc_u32_to_float((uint32_t)speed);
+		le32enc(buf, fval);
+		if (asmc_key_write(dev, fankey, buf, 4) != 0)
+			return (-1);
+	} else {
+		speed *= 4;
+		buf[0] = speed >> 8;
+		buf[1] = speed;
+		if (asmc_key_write(dev, fankey, buf, 2) != 0)
+			return (-1);
+	}
 
 	return (0);
 }
@@ -2016,11 +2114,35 @@ static int
 asmc_mb_sysctl_fanmanual(SYSCTL_HANDLER_ARGS)
 {
 	device_t dev = (device_t)arg1;
+	struct asmc_softc *sc = device_get_softc(dev);
 	int fan = arg2;
 	int error;
 	int32_t v;
 	uint8_t buf[2];
 	uint16_t val;
+	char fmkey[5];
+
+	/*
+	 * T2 Macs use per-fan F%dMd keys (1 byte each).
+	 * Standard Macs use FS! bitmask (2 bytes).
+	 */
+	snprintf(fmkey, sizeof(fmkey), ASMC_KEY_FANMANUAL_T2, fan);
+	if (sc->sc_is_t2 &&
+	    asmc_key_getinfo(dev, fmkey, NULL, NULL) == 0) {
+		error = asmc_key_read(dev, fmkey, buf, 1);
+		if (error != 0)
+			return (error);
+		v = buf[0] ? 1 : 0;
+
+		error = sysctl_handle_int(oidp, &v, 0, req);
+		if (error == 0 && req->newptr != NULL) {
+			if (v != 0 && v != 1)
+				return (EINVAL);
+			buf[0] = (uint8_t)v;
+			error = asmc_key_write(dev, fmkey, buf, 1);
+		}
+		return (error);
+	}
 
 	/* Read current FS! bitmask (asmc_key_read locks internally) */
 	error = asmc_key_read(dev, ASMC_KEY_FANMANUAL, buf, sizeof(buf));

sys/dev/asmc/asmcmmio.c

@@ -0,0 +1,402 @@
+/*
+ * Copyright (c) 2026 Abdelkader Boudih <freebsd@seuros.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+/*
+ * MMIO backend for Apple SMC (T2 and later Macs).
+ *
+ * T2 Macs expose the SMC via memory-mapped registers instead of I/O ports.
+ * Protocol: clear status, write key/cmd, poll for ready, read result.
+ */
+
+#include <sys/param.h>
+#include <sys/bus.h>
+#include <sys/endian.h>
+#include <sys/kernel.h>
+#include <sys/lock.h>
+#include <sys/mutex.h>
+#include <sys/module.h>
+#include <sys/rman.h>
+#include <sys/sysctl.h>
+#include <sys/systm.h>
+#include <sys/taskqueue.h>
+
+#include <machine/bus.h>
+
+#include <dev/asmc/asmcvar.h>
+#include <dev/asmc/asmcmmio.h>
+
+/*
+ * Wait for MMIO status register bit 5 (ready) with exponential backoff.
+ * Caller must hold sc_mtx.
+ */
+static int
+asmc_mmio_wait(device_t dev)
+{
+	struct asmc_softc *sc = device_get_softc(dev);
+	int i;
+	uint8_t status;
+	int delay_us = 10;
+
+	for (i = 0; i < ASMC_MMIO_MAX_WAIT; i++) {
+		status = bus_read_1(sc->sc_iomem, ASMC_MMIO_STATUS);
+		if (status & ASMC_MMIO_STATUS_READY)
+			return (0);
+		DELAY(delay_us);
+		if (delay_us < 3200)
+			delay_us *= 2;
+	}
+
+	return (ETIMEDOUT);
+}
+
+int
+asmc_mmio_key_read(device_t dev, const char *key, uint8_t *buf, uint8_t len)
+{
+	struct asmc_softc *sc = device_get_softc(dev);
+	uint32_t key_int;
+	int error, i;
+	uint8_t cmd_result, rlen;
+
+	if (len > ASMC_MAXVAL)
+		return (EINVAL);
+
+	mtx_lock_spin(&sc->sc_mtx);
+
+	/* Clear status if non-zero */
+	if (bus_read_1(sc->sc_iomem, ASMC_MMIO_STATUS))
+		bus_write_1(sc->sc_iomem, ASMC_MMIO_STATUS, 0);
+
+	/* Write key name as raw 4 bytes */
+	memcpy(&key_int, key, 4);
+	bus_write_4(sc->sc_iomem, ASMC_MMIO_KEY_NAME, key_int);
+
+	/* Write SMC ID (always 0) and command */
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_SMC_ID, 0);
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_CMD, ASMC_CMDREAD);
+
+	/* Wait for ready */
+	error = asmc_mmio_wait(dev);
+	if (error != 0) {
+		uint8_t st = bus_read_1(sc->sc_iomem, ASMC_MMIO_STATUS);
+		uint8_t cm = bus_read_1(sc->sc_iomem, ASMC_MMIO_CMD);
+		mtx_unlock_spin(&sc->sc_mtx);
+		device_printf(dev,
+		    "%s: timeout key %.4s status=0x%02x cmd=0x%02x\n",
+		    __func__, key, st, cm);
+		return (error);
+	}
+
+	/* Check command result (0 = success, 0x84 = key not found) */
+	cmd_result = bus_read_1(sc->sc_iomem, ASMC_MMIO_CMD);
+	if (cmd_result != 0) {
+		mtx_unlock_spin(&sc->sc_mtx);
+		device_printf(dev,
+		    "%s: key %.4s cmd error 0x%02x\n",
+		    __func__, key, cmd_result);
+		return (EIO);
+	}
+
+	/* Read data length and data bytes; zero-fill remainder */
+	rlen = bus_read_1(sc->sc_iomem, ASMC_MMIO_DATA_LEN);
+	rlen = MIN(rlen, len);
+	for (i = rlen; i < len; i++)
+		buf[i] = 0;
+	for (i = 0; i < rlen; i++)
+		buf[i] = bus_read_1(sc->sc_iomem, ASMC_MMIO_DATA + i);
+
+	mtx_unlock_spin(&sc->sc_mtx);
+	return (0);
+}
+
+int
+asmc_mmio_key_write(device_t dev, const char *key, uint8_t *buf, uint8_t len)
+{
+	struct asmc_softc *sc = device_get_softc(dev);
+	uint32_t key_int;
+	int error, i;
+	uint8_t cmd_result;
+
+	if (len > ASMC_MAXVAL)
+		return (EINVAL);
+
+	mtx_lock_spin(&sc->sc_mtx);
+
+	/* Clear status */
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_STATUS, 0);
+
+	/* Write data bytes first */
+	for (i = 0; i < len; i++)
+		bus_write_1(sc->sc_iomem, ASMC_MMIO_DATA + i, buf[i]);
+
+	/* Write key name as raw 4 bytes */
+	memcpy(&key_int, key, 4);
+	bus_write_4(sc->sc_iomem, ASMC_MMIO_KEY_NAME, key_int);
+
+	/* Write length, SMC ID, command */
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_DATA_LEN, len);
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_SMC_ID, 0);
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_CMD, ASMC_CMDWRITE);
+
+	/* Wait for ready */
+	error = asmc_mmio_wait(dev);
+	if (error != 0) {
+		mtx_unlock_spin(&sc->sc_mtx);
+		device_printf(dev, "%s: timeout writing key %.4s\n",
+		    __func__, key);
+		return (error);
+	}
+
+	cmd_result = bus_read_1(sc->sc_iomem, ASMC_MMIO_CMD);
+	mtx_unlock_spin(&sc->sc_mtx);
+
+	return (cmd_result == 0 ? 0 : EIO);
+}
+
+int
+asmc_mmio_key_getinfo(device_t dev, const char *key, uint8_t *len, char *type)
+{
+	struct asmc_softc *sc = device_get_softc(dev);
+	uint32_t key_int;
+	int error, i;
+	uint8_t cmd_result;
+
+	mtx_lock_spin(&sc->sc_mtx);
+
+	/* Clear status */
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_STATUS, 0);
+
+	/* Write key name as raw 4 bytes */
+	memcpy(&key_int, key, 4);
+	bus_write_4(sc->sc_iomem, ASMC_MMIO_KEY_NAME, key_int);
+
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_SMC_ID, 0);
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_CMD, ASMC_CMDGETINFO);
+
+	error = asmc_mmio_wait(dev);
+	if (error != 0) {
+		mtx_unlock_spin(&sc->sc_mtx);
+		return (error);
+	}
+
+	cmd_result = bus_read_1(sc->sc_iomem, ASMC_MMIO_CMD);
+	if (cmd_result != 0) {
+		mtx_unlock_spin(&sc->sc_mtx);
+		return (EIO);
+	}
+
+	/*
+	 * GETINFO response layout (MMIO):
+	 *   data[0..3] = type code (4 chars)
+	 *   data[4]    = reserved
+	 *   data[5]    = data length
+	 *   data[6]    = flags/attributes
+	 */
+	if (type != NULL) {
+		for (i = 0; i < ASMC_TYPELEN; i++)
+			type[i] = bus_read_1(sc->sc_iomem,
+			    ASMC_MMIO_DATA + i);
+		type[ASMC_TYPELEN] = '\0';
+	}
+	if (len != NULL)
+		*len = bus_read_1(sc->sc_iomem, ASMC_MMIO_DATA + 5);
+
+	mtx_unlock_spin(&sc->sc_mtx);
+	return (0);
+}
+
+int
+asmc_mmio_key_getbyindex(device_t dev, int index, char *key)
+{
+	struct asmc_softc *sc = device_get_softc(dev);
+	uint32_t idx_val;
+	int error, i;
+	uint8_t cmd_result;
+
+	mtx_lock_spin(&sc->sc_mtx);
+
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_STATUS, 0);
+
+	/* Write index as big-endian 4 bytes to key name register */
+	idx_val = htobe32(index);
+	bus_write_4(sc->sc_iomem, ASMC_MMIO_KEY_NAME, idx_val);
+
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_SMC_ID, 0);
+	bus_write_1(sc->sc_iomem, ASMC_MMIO_CMD, ASMC_CMDGETBYINDEX);
+
+	error = asmc_mmio_wait(dev);
+	if (error != 0) {
+		mtx_unlock_spin(&sc->sc_mtx);
+		return (error);
+	}
+
+	cmd_result = bus_read_1(sc->sc_iomem, ASMC_MMIO_CMD);
+	if (cmd_result != 0) {
+		mtx_unlock_spin(&sc->sc_mtx);
+		return (EIO);
+	}
+
+	/* Result: 4-byte key name in DATA */
+	for (i = 0; i < ASMC_KEYLEN; i++)
+		key[i] = bus_read_1(sc->sc_iomem, ASMC_MMIO_DATA + i);
+	key[ASMC_KEYLEN] = '\0';
+
+	mtx_unlock_spin(&sc->sc_mtx);
+	return (0);
+}
+
+/*
+ * Validate MMIO and detect T2.
+ * Check that status register is accessible and LDKN firmware version >= 2.
+ */
+int
+asmc_mmio_probe(device_t dev)
+{
+	struct asmc_softc *sc = device_get_softc(dev);
+	rman_res_t size;
+	uint8_t status, ldkn;
+	int error;
+
+	size = rman_get_size(sc->sc_iomem);
+	if (size < ASMC_MMIO_MIN_SIZE) {
+		device_printf(dev, "MMIO region too small (%jd < %d)\n",
+		    (intmax_t)size, ASMC_MMIO_MIN_SIZE);
+		return (ENXIO);
+	}
+
+	/* Check status register isn't stuck at 0xFF */
+	status = bus_read_1(sc->sc_iomem, ASMC_MMIO_STATUS);
+	if (status == 0xFF) {
+		device_printf(dev, "MMIO status register reads 0xFF\n");
+		return (ENXIO);
+	}
+
+	/*
+	 * We need the mutex initialized before calling mmio_key_read,
+	 * but attach hasn't done it yet. Initialize early.
+	 */
+	if (!mtx_initialized(&sc->sc_mtx))
+		mtx_init(&sc->sc_mtx, "asmc", NULL, MTX_SPIN);
+
+	/* Read LDKN (firmware version) -- must be >= 2 for MMIO */
+	error = asmc_mmio_key_read(dev, ASMC_KEY_LDKN, &ldkn, 1);
+	if (error != 0) {
+		device_printf(dev, "MMIO: failed to read LDKN key\n");
+		return (ENXIO);
+	}
+
+	if (ldkn < 2) {
+		device_printf(dev, "MMIO: LDKN=%d (need >= 2)\n", ldkn);
+		return (ENXIO);
+	}
+
+	device_printf(dev, "MMIO: LDKN=%d, T2 SMC detected\n", ldkn);
+	sc->sc_is_t2 = 1;
+
+	return (0);
+}
+
+void
+asmc_mmio_detach(device_t dev, struct asmc_softc *sc)
+{
+
+	if (sc->sc_iomem != NULL) {
+		bus_release_resource(dev, SYS_RES_MEMORY, sc->sc_rid_mem,
+		    sc->sc_iomem);
+		sc->sc_iomem = NULL;
+	}
+	sc->sc_is_mmio = 0;
+	sc->sc_is_t2 = 0;
+}
+
+/*
+ * Convert IEEE 754 float (as u32) to unsigned integer.
+ * Kernel soft-float: extract integer part only.
+ * Used for T2 fan RPM values (always positive, reasonable range).
+ */
+uint32_t
+asmc_float_to_u32(uint32_t d)
+{
+	int32_t exp;
+	uint32_t fr;
+
+	/* Negative or zero */
+	if (d == 0 || (d >> 31) != 0)
+		return (0);
+
+	exp = (int32_t)((d >> 23) & 0xff) - 0x7f;
+	fr = d & 0x7fffff;	/* 23-bit mantissa */
+
+	if (exp < 0)
+		return (0);
+	if (exp > 23) {
+		if (exp > 30)
+			return (0xffffffffu);
+		return ((1u << exp) | (fr << (exp - 23)));
+	}
+	/* Normal case: 0 <= exp <= 23 */
+	return ((1u << exp) + (fr >> (23 - exp)));
+}
+
+/*
+ * Convert unsigned integer to IEEE 754 float (as u32).
+ * Only handles values in fan RPM range (0-65535).
+ */
+uint32_t
+asmc_u32_to_float(uint32_t d)
+{
+	uint32_t dc, bc, exp;
+
+	if (d == 0)
+		return (0);
+
+	/* Find highest set bit position */
+	dc = d;
+	bc = 0;
+	while (dc >>= 1)
+		++bc;
+
+	bc = MIN(bc, 30);
+
+	exp = 0x7f + bc;
+
+	/*
+	 * Mantissa: strip the implicit leading 1-bit and place
+	 * remaining bits into the 23-bit mantissa field.
+	 */
+	if (bc >= 23)
+		return ((exp << 23) | ((d >> (bc - 23)) & 0x7fffff));
+	else
+		return ((exp << 23) | ((d << (23 - bc)) & 0x7fffff));
+}
+
+/*
+ * Battery charge limit sysctl (T2 Macs).
+ * BCLM key: 1 byte, 0-100 (percentage).
+ */
+int
+asmc_bclm_sysctl(SYSCTL_HANDLER_ARGS)
+{
+	device_t dev = (device_t)arg1;
+	uint8_t bclm;
+	int val, error;
+
+	error = asmc_mmio_key_read(dev, ASMC_KEY_BCLM, &bclm, 1);
+	if (error != 0)
+		return (EIO);
+
+	val = (int)bclm;
+	error = sysctl_handle_int(oidp, &val, 0, req);
+	if (error != 0 || req->newptr == NULL)
+		return (error);
+
+	if (val < 0 || val > 100)
+		return (EINVAL);
+
+	bclm = (uint8_t)val;
+	error = asmc_mmio_key_write(dev, ASMC_KEY_BCLM, &bclm, 1);
+
+	return (error != 0 ? EIO : 0);
+}

sys/dev/asmc/asmcmmio.h

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2026 Abdelkader Boudih <freebsd@seuros.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#ifndef _DEV_ASMC_ASMCMMIO_H_
+#define _DEV_ASMC_ASMCMMIO_H_
+
+struct asmc_softc;
+
+/*
+ * MMIO register offsets.
+ */
+#define ASMC_MMIO_DATA		0x0000
+#define ASMC_MMIO_KEY_NAME	0x0078
+#define ASMC_MMIO_DATA_LEN	0x007D
+#define ASMC_MMIO_SMC_ID	0x007E
+#define ASMC_MMIO_CMD		0x007F
+#define ASMC_MMIO_STATUS	0x4005
+#define ASMC_MMIO_MIN_SIZE	0x4006
+#define ASMC_MMIO_STATUS_READY	0x20	/* Bit 5 */
+#define ASMC_MMIO_MAX_WAIT	24
+
+/*
+ * T2-specific keys.
+ */
+#define ASMC_KEY_LDKN		"LDKN"	/* RO; 1 byte, firmware version */
+#define ASMC_KEY_BCLM		"BCLM"	/* RW; 1 byte, battery charge limit 0-100 */
+#define ASMC_KEY_FANMANUAL_T2	"F%dMd"	/* RW; 1 byte per fan (T2) */
+
+/*
+ * MMIO backend functions.
+ */
+int	asmc_mmio_probe(device_t dev);
+void	asmc_mmio_detach(device_t dev, struct asmc_softc *sc);
+int	asmc_mmio_key_read(device_t dev, const char *key,
+	    uint8_t *buf, uint8_t len);
+int	asmc_mmio_key_write(device_t dev, const char *key,
+	    uint8_t *buf, uint8_t len);
+int	asmc_mmio_key_getinfo(device_t dev, const char *key,
+	    uint8_t *len, char *type);
+int	asmc_mmio_key_getbyindex(device_t dev, int index, char *key);
+
+/*
+ * IEEE 754 float <-> uint32 conversion for T2 fan RPM values.
+ */
+uint32_t	asmc_float_to_u32(uint32_t d);
+uint32_t	asmc_u32_to_float(uint32_t d);
+
+/*
+ * T2-specific sysctls.
+ */
+int	asmc_bclm_sysctl(SYSCTL_HANDLER_ARGS);
+
+#endif /* _DEV_ASMC_ASMCMMIO_H_ */

sys/dev/asmc/asmcvar.h

@@ -53,6 +53,11 @@ struct asmc_softc {
 	struct resource 	*sc_ioport;
 	struct resource 	*sc_irq;
 	void 			*sc_cookie;
+	/* MMIO backend (T2 Macs) */
+	int			sc_rid_mem;
+	struct resource		*sc_iomem;
+	int			sc_is_mmio;
+	int			sc_is_t2;	/* T2 fan float + per-fan manual */
 	int 			sc_sms_intrtype;
 	struct taskqueue 	*sc_sms_tq;
 	struct task 		sc_sms_task;

sys/modules/asmc/Makefile

@@ -1,7 +1,7 @@
 .PATH: ${SRCTOP}/sys/dev/asmc
 
 KMOD=	asmc
-SRCS=	asmc.c opt_acpi.h opt_asmc.h
+SRCS=	asmc.c asmcmmio.c opt_acpi.h opt_asmc.h
 SRCS+=	acpi_if.h backlight_if.h bus_if.h device_if.h
 
 .include <bsd.kmod.mk>