diff --git a/Documentation/driver-api/surface_aggregator/clients/index.rst b/Documentation/driver-api/surface_aggregator/clients/index.rst
index ab260ec82cfb..3ccabce23271 100644
--- a/Documentation/driver-api/surface_aggregator/clients/index.rst
+++ b/Documentation/driver-api/surface_aggregator/clients/index.rst
@@ -11,6 +11,7 @@ This is the documentation for client drivers themselves. Refer to
    :maxdepth: 1

    cdev
+   san

 .. only::  subproject and html

diff --git a/Documentation/driver-api/surface_aggregator/clients/san.rst b/Documentation/driver-api/surface_aggregator/clients/san.rst
new file mode 100644
index 000000000000..38c2580e7758
--- /dev/null
+++ b/Documentation/driver-api/surface_aggregator/clients/san.rst
@@ -0,0 +1,44 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+.. |san_client_link| replace:: :c:func:`san_client_link`
+.. |san_dgpu_notifier_register| replace:: :c:func:`san_dgpu_notifier_register`
+.. |san_dgpu_notifier_unregister| replace:: :c:func:`san_dgpu_notifier_unregister`
+
+===================
+Surface ACPI Notify
+===================
+
+The Surface ACPI Notify (SAN) device provides the bridge between ACPI and
+SAM controller. Specifically, ACPI code can execute requests and handle
+battery and thermal events via this interface. In addition to this, events
+relating to the discrete GPU (dGPU) of the Surface Book 2 can be sent from
+ACPI code (note: the Surface Book 3 uses a different method for this). The
+only currently known event sent via this interface is a dGPU power-on
+notification. While this driver handles the former part internally, it only
+relays the dGPU events to any other driver interested via its public API and
+does not handle them.
+
+The public interface of this driver is split into two parts: Client
+registration and notifier-block registration.
+
+A client to the SAN interface can be linked as consumer to the SAN device
+via |san_client_link|. This can be used to ensure that the a client
+receiving dGPU events does not miss any events due to the SAN interface not
+being set up as this forces the client driver to unbind once the SAN driver
+is unbound.
+
+Notifier-blocks can be registered by any device for as long as the module is
+loaded, regardless of being linked as client or not. Registration is done
+with |san_dgpu_notifier_register|. If the notifier is not needed any more, it
+should be unregistered via |san_dgpu_notifier_unregister|.
+
+Consult the API documentation below for more details.
+
+
+API Documentation
+=================
+
+.. kernel-doc:: include/linux/surface_acpi_notify.h
+
+.. kernel-doc:: drivers/platform/surface/surface_acpi_notify.c
+    :export:
diff --git a/MAINTAINERS b/MAINTAINERS
index f5a788f445a4..894c9ef1b8d6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11699,7 +11699,9 @@ W:	https://github.com/linux-surface/surface-aggregator-module
 C:	irc://chat.freenode.net/##linux-surface
 F:	Documentation/driver-api/surface_aggregator/
 F:	drivers/platform/surface/aggregator/
+F:	drivers/platform/surface/surface_acpi_notify.c
 F:	drivers/platform/surface/surface_aggregator_cdev.c
+F:	include/linux/surface_acpi_notify.h
 F:	include/linux/surface_aggregator/
 F:	include/uapi/linux/surface_aggregator/

diff --git a/drivers/platform/surface/Kconfig b/drivers/platform/surface/Kconfig
index cecad7a0cb7b..88818320105e 100644
--- a/drivers/platform/surface/Kconfig
+++ b/drivers/platform/surface/Kconfig
@@ -40,6 +40,25 @@ config SURFACE_3_POWER_OPREGION
 	  This driver provides support for ACPI operation
 	  region of the Surface 3 battery platform driver.

+config SURFACE_ACPI_NOTIFY
+	tristate "Surface ACPI Notify Driver"
+	depends on SURFACE_AGGREGATOR
+	help
+	  Surface ACPI Notify (SAN) driver for Microsoft Surface devices.
+
+	  This driver provides support for the ACPI interface (called SAN) of
+	  the Surface System Aggregator Module (SSAM) EC. This interface is used
+	  on 5th- and 6th-generation Microsoft Surface devices (including
+	  Surface Pro 5 and 6, Surface Book 2, Surface Laptops 1 and 2, and in
+	  reduced functionality on the Surface Laptop 3) to execute SSAM
+	  requests directly from ACPI code, as well as receive SSAM events and
+	  turn them into ACPI notifications. It essentially acts as a
+	  translation layer between the SSAM controller and ACPI.
+
+	  Specifically, this driver may be needed for battery status reporting,
+	  thermal sensor access, and real-time clock information, depending on
+	  the Surface device in question.
+
 config SURFACE_AGGREGATOR_CDEV
 	tristate "Surface System Aggregator Module User-Space Interface"
 	depends on SURFACE_AGGREGATOR
diff --git a/drivers/platform/surface/Makefile b/drivers/platform/surface/Makefile
index 161f0ad05795..3eb971006877 100644
--- a/drivers/platform/surface/Makefile
+++ b/drivers/platform/surface/Makefile
@@ -7,6 +7,7 @@
 obj-$(CONFIG_SURFACE3_WMI)		+= surface3-wmi.o
 obj-$(CONFIG_SURFACE_3_BUTTON)		+= surface3_button.o
 obj-$(CONFIG_SURFACE_3_POWER_OPREGION)	+= surface3_power.o
+obj-$(CONFIG_SURFACE_ACPI_NOTIFY)	+= surface_acpi_notify.o
 obj-$(CONFIG_SURFACE_AGGREGATOR)	+= aggregator/
 obj-$(CONFIG_SURFACE_AGGREGATOR_CDEV)	+= surface_aggregator_cdev.o
 obj-$(CONFIG_SURFACE_GPE)		+= surface_gpe.o
diff --git a/drivers/platform/surface/surface_acpi_notify.c b/drivers/platform/surface/surface_acpi_notify.c
new file mode 100644
index 000000000000..8cd67a669c86
--- /dev/null
+++ b/drivers/platform/surface/surface_acpi_notify.c
@@ -0,0 +1,886 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for the Surface ACPI Notify (SAN) interface/shim.
+ *
+ * Translates communication from ACPI to Surface System Aggregator Module
+ * (SSAM/SAM) requests and back, specifically SAM-over-SSH. Translates SSAM
+ * events back to ACPI notifications. Allows handling of discrete GPU
+ * notifications sent from ACPI via the SAN interface by providing them to any
+ * registered external driver.
+ *
+ * Copyright (C) 2019-2020 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#include <asm/unaligned.h>
+#include <linux/acpi.h>
+#include <linux/delay.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/notifier.h>
+#include <linux/platform_device.h>
+#include <linux/rwsem.h>
+
+#include <linux/surface_aggregator/controller.h>
+#include <linux/surface_acpi_notify.h>
+
+struct san_data {
+	struct device *dev;
+	struct ssam_controller *ctrl;
+
+	struct acpi_connection_info info;
+
+	struct ssam_event_notifier nf_bat;
+	struct ssam_event_notifier nf_tmp;
+};
+
+#define to_san_data(ptr, member) \
+	container_of(ptr, struct san_data, member)
+
+
+/* -- dGPU notifier interface. ---------------------------------------------- */
+
+struct san_rqsg_if {
+	struct rw_semaphore lock;
+	struct device *dev;
+	struct blocking_notifier_head nh;
+};
+
+static struct san_rqsg_if san_rqsg_if = {
+	.lock = __RWSEM_INITIALIZER(san_rqsg_if.lock),
+	.dev = NULL,
+	.nh = BLOCKING_NOTIFIER_INIT(san_rqsg_if.nh),
+};
+
+static int san_set_rqsg_interface_device(struct device *dev)
+{
+	int status = 0;
+
+	down_write(&san_rqsg_if.lock);
+	if (!san_rqsg_if.dev && dev)
+		san_rqsg_if.dev = dev;
+	else
+		status = -EBUSY;
+	up_write(&san_rqsg_if.lock);
+
+	return status;
+}
+
+/**
+ * san_client_link() - Link client as consumer to SAN device.
+ * @client: The client to link.
+ *
+ * Sets up a device link between the provided client device as consumer and
+ * the SAN device as provider. This function can be used to ensure that the
+ * SAN interface has been set up and will be set up for as long as the driver
+ * of the client device is bound. This guarantees that, during that time, all
+ * dGPU events will be received by any registered notifier.
+ *
+ * The link will be automatically removed once the client device's driver is
+ * unbound.
+ *
+ * Return: Returns zero on success, %-ENXIO if the SAN interface has not been
+ * set up yet, and %-ENOMEM if device link creation failed.
+ */
+int san_client_link(struct device *client)
+{
+	const u32 flags = DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER;
+	struct device_link *link;
+
+	down_read(&san_rqsg_if.lock);
+
+	if (!san_rqsg_if.dev) {
+		up_read(&san_rqsg_if.lock);
+		return -ENXIO;
+	}
+
+	link = device_link_add(client, san_rqsg_if.dev, flags);
+	if (!link) {
+		up_read(&san_rqsg_if.lock);
+		return -ENOMEM;
+	}
+
+	if (READ_ONCE(link->status) == DL_STATE_SUPPLIER_UNBIND) {
+		up_read(&san_rqsg_if.lock);
+		return -ENXIO;
+	}
+
+	up_read(&san_rqsg_if.lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(san_client_link);
+
+/**
+ * san_dgpu_notifier_register() - Register a SAN dGPU notifier.
+ * @nb: The notifier-block to register.
+ *
+ * Registers a SAN dGPU notifier, receiving any new SAN dGPU events sent from
+ * ACPI. The registered notifier will be called with &struct san_dgpu_event
+ * as notifier data and the command ID of that event as notifier action.
+ */
+int san_dgpu_notifier_register(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&san_rqsg_if.nh, nb);
+}
+EXPORT_SYMBOL_GPL(san_dgpu_notifier_register);
+
+/**
+ * san_dgpu_notifier_unregister() - Unregister a SAN dGPU notifier.
+ * @nb: The notifier-block to unregister.
+ */
+int san_dgpu_notifier_unregister(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&san_rqsg_if.nh, nb);
+}
+EXPORT_SYMBOL_GPL(san_dgpu_notifier_unregister);
+
+static int san_dgpu_notifier_call(struct san_dgpu_event *evt)
+{
+	int ret;
+
+	ret = blocking_notifier_call_chain(&san_rqsg_if.nh, evt->command, evt);
+	return notifier_to_errno(ret);
+}
+
+
+/* -- ACPI _DSM event relay. ------------------------------------------------ */
+
+#define SAN_DSM_REVISION	0
+
+/* 93b666c5-70c6-469f-a215-3d487c91ab3c */
+static const guid_t SAN_DSM_UUID =
+	GUID_INIT(0x93b666c5, 0x70c6, 0x469f, 0xa2, 0x15, 0x3d,
+		  0x48, 0x7c, 0x91, 0xab, 0x3c);
+
+enum san_dsm_event_fn {
+	SAN_DSM_EVENT_FN_BAT1_STAT = 0x03,
+	SAN_DSM_EVENT_FN_BAT1_INFO = 0x04,
+	SAN_DSM_EVENT_FN_ADP1_STAT = 0x05,
+	SAN_DSM_EVENT_FN_ADP1_INFO = 0x06,
+	SAN_DSM_EVENT_FN_BAT2_STAT = 0x07,
+	SAN_DSM_EVENT_FN_BAT2_INFO = 0x08,
+	SAN_DSM_EVENT_FN_THERMAL   = 0x09,
+	SAN_DSM_EVENT_FN_DPTF      = 0x0a,
+};
+
+enum sam_event_cid_bat {
+	SAM_EVENT_CID_BAT_BIX  = 0x15,
+	SAM_EVENT_CID_BAT_BST  = 0x16,
+	SAM_EVENT_CID_BAT_ADP  = 0x17,
+	SAM_EVENT_CID_BAT_PROT = 0x18,
+	SAM_EVENT_CID_BAT_DPTF = 0x4f,
+};
+
+enum sam_event_cid_tmp {
+	SAM_EVENT_CID_TMP_TRIP = 0x0b,
+};
+
+struct san_event_work {
+	struct delayed_work work;
+	struct device *dev;
+	struct ssam_event event;	/* must be last */
+};
+
+static int san_acpi_notify_event(struct device *dev, u64 func,
+				 union acpi_object *param)
+{
+	acpi_handle san = ACPI_HANDLE(dev);
+	union acpi_object *obj;
+	int status = 0;
+
+	if (!acpi_check_dsm(san, &SAN_DSM_UUID, SAN_DSM_REVISION, 1 << func))
+		return 0;
+
+	dev_dbg(dev, "notify event %#04llx\n", func);
+
+	obj = acpi_evaluate_dsm_typed(san, &SAN_DSM_UUID, SAN_DSM_REVISION,
+				      func, param, ACPI_TYPE_BUFFER);
+	if (!obj)
+		return -EFAULT;
+
+	if (obj->buffer.length != 1 || obj->buffer.pointer[0] != 0) {
+		dev_err(dev, "got unexpected result from _DSM\n");
+		status = -EPROTO;
+	}
+
+	ACPI_FREE(obj);
+	return status;
+}
+
+static int san_evt_bat_adp(struct device *dev, const struct ssam_event *event)
+{
+	int status;
+
+	status = san_acpi_notify_event(dev, SAN_DSM_EVENT_FN_ADP1_STAT, NULL);
+	if (status)
+		return status;
+
+	/*
+	 * Ensure that the battery states get updated correctly. When the
+	 * battery is fully charged and an adapter is plugged in, it sometimes
+	 * is not updated correctly, instead showing it as charging.
+	 * Explicitly trigger battery updates to fix this.
+	 */
+
+	status = san_acpi_notify_event(dev, SAN_DSM_EVENT_FN_BAT1_STAT, NULL);
+	if (status)
+		return status;
+
+	return san_acpi_notify_event(dev, SAN_DSM_EVENT_FN_BAT2_STAT, NULL);
+}
+
+static int san_evt_bat_bix(struct device *dev, const struct ssam_event *event)
+{
+	enum san_dsm_event_fn fn;
+
+	if (event->instance_id == 0x02)
+		fn = SAN_DSM_EVENT_FN_BAT2_INFO;
+	else
+		fn = SAN_DSM_EVENT_FN_BAT1_INFO;
+
+	return san_acpi_notify_event(dev, fn, NULL);
+}
+
+static int san_evt_bat_bst(struct device *dev, const struct ssam_event *event)
+{
+	enum san_dsm_event_fn fn;
+
+	if (event->instance_id == 0x02)
+		fn = SAN_DSM_EVENT_FN_BAT2_STAT;
+	else
+		fn = SAN_DSM_EVENT_FN_BAT1_STAT;
+
+	return san_acpi_notify_event(dev, fn, NULL);
+}
+
+static int san_evt_bat_dptf(struct device *dev, const struct ssam_event *event)
+{
+	union acpi_object payload;
+
+	/*
+	 * The Surface ACPI expects a buffer and not a package. It specifically
+	 * checks for ObjectType (Arg3) == 0x03. This will cause a warning in
+	 * acpica/nsarguments.c, but that warning can be safely ignored.
+	 */
+	payload.type = ACPI_TYPE_BUFFER;
+	payload.buffer.length = event->length;
+	payload.buffer.pointer = (u8 *)&event->data[0];
+
+	return san_acpi_notify_event(dev, SAN_DSM_EVENT_FN_DPTF, &payload);
+}
+
+static unsigned long san_evt_bat_delay(u8 cid)
+{
+	switch (cid) {
+	case SAM_EVENT_CID_BAT_ADP:
+		/*
+		 * Wait for battery state to update before signaling adapter
+		 * change.
+		 */
+		return msecs_to_jiffies(5000);
+
+	case SAM_EVENT_CID_BAT_BST:
+		/* Ensure we do not miss anything important due to caching. */
+		return msecs_to_jiffies(2000);
+
+	default:
+		return 0;
+	}
+}
+
+static bool san_evt_bat(const struct ssam_event *event, struct device *dev)
+{
+	int status;
+
+	switch (event->command_id) {
+	case SAM_EVENT_CID_BAT_BIX:
+		status = san_evt_bat_bix(dev, event);
+		break;
+
+	case SAM_EVENT_CID_BAT_BST:
+		status = san_evt_bat_bst(dev, event);
+		break;
+
+	case SAM_EVENT_CID_BAT_ADP:
+		status = san_evt_bat_adp(dev, event);
+		break;
+
+	case SAM_EVENT_CID_BAT_PROT:
+		/*
+		 * TODO: Implement support for battery protection status change
+		 *       event.
+		 */
+		return true;
+
+	case SAM_EVENT_CID_BAT_DPTF:
+		status = san_evt_bat_dptf(dev, event);
+		break;
+
+	default:
+		return false;
+	}
+
+	if (status) {
+		dev_err(dev, "error handling power event (cid = %#04x)\n",
+			event->command_id);
+	}
+
+	return true;
+}
+
+static void san_evt_bat_workfn(struct work_struct *work)
+{
+	struct san_event_work *ev;
+
+	ev = container_of(work, struct san_event_work, work.work);
+	san_evt_bat(&ev->event, ev->dev);
+	kfree(ev);
+}
+
+static u32 san_evt_bat_nf(struct ssam_event_notifier *nf,
+			  const struct ssam_event *event)
+{
+	struct san_data *d = to_san_data(nf, nf_bat);
+	struct san_event_work *work;
+	unsigned long delay = san_evt_bat_delay(event->command_id);
+
+	if (delay == 0)
+		return san_evt_bat(event, d->dev) ? SSAM_NOTIF_HANDLED : 0;
+
+	work = kzalloc(sizeof(*work) + event->length, GFP_KERNEL);
+	if (!work)
+		return ssam_notifier_from_errno(-ENOMEM);
+
+	INIT_DELAYED_WORK(&work->work, san_evt_bat_workfn);
+	work->dev = d->dev;
+
+	memcpy(&work->event, event, sizeof(struct ssam_event) + event->length);
+
+	schedule_delayed_work(&work->work, delay);
+	return SSAM_NOTIF_HANDLED;
+}
+
+static int san_evt_tmp_trip(struct device *dev, const struct ssam_event *event)
+{
+	union acpi_object param;
+
+	/*
+	 * The Surface ACPI expects an integer and not a package. This will
+	 * cause a warning in acpica/nsarguments.c, but that warning can be
+	 * safely ignored.
+	 */
+	param.type = ACPI_TYPE_INTEGER;
+	param.integer.value = event->instance_id;
+
+	return san_acpi_notify_event(dev, SAN_DSM_EVENT_FN_THERMAL, &param);
+}
+
+static bool san_evt_tmp(const struct ssam_event *event, struct device *dev)
+{
+	int status;
+
+	switch (event->command_id) {
+	case SAM_EVENT_CID_TMP_TRIP:
+		status = san_evt_tmp_trip(dev, event);
+		break;
+
+	default:
+		return false;
+	}
+
+	if (status) {
+		dev_err(dev, "error handling thermal event (cid = %#04x)\n",
+			event->command_id);
+	}
+
+	return true;
+}
+
+static u32 san_evt_tmp_nf(struct ssam_event_notifier *nf,
+			  const struct ssam_event *event)
+{
+	struct san_data *d = to_san_data(nf, nf_tmp);
+
+	return san_evt_tmp(event, d->dev) ? SSAM_NOTIF_HANDLED : 0;
+}
+
+
+/* -- ACPI GSB OperationRegion handler -------------------------------------- */
+
+struct gsb_data_in {
+	u8 cv;
+} __packed;
+
+struct gsb_data_rqsx {
+	u8 cv;				/* Command value (san_gsb_request_cv). */
+	u8 tc;				/* Target category. */
+	u8 tid;				/* Target ID. */
+	u8 iid;				/* Instance ID. */
+	u8 snc;				/* Expect-response-flag. */
+	u8 cid;				/* Command ID. */
+	u16 cdl;			/* Payload length. */
+	u8 pld[];			/* Payload. */
+} __packed;
+
+struct gsb_data_etwl {
+	u8 cv;				/* Command value (should be 0x02). */
+	u8 etw3;			/* Unknown. */
+	u8 etw4;			/* Unknown. */
+	u8 msg[];			/* Error message (ASCIIZ). */
+} __packed;
+
+struct gsb_data_out {
+	u8 status;			/* _SSH communication status. */
+	u8 len;				/* _SSH payload length. */
+	u8 pld[];			/* _SSH payload. */
+} __packed;
+
+union gsb_buffer_data {
+	struct gsb_data_in   in;	/* Common input. */
+	struct gsb_data_rqsx rqsx;	/* RQSX input. */
+	struct gsb_data_etwl etwl;	/* ETWL input. */
+	struct gsb_data_out  out;	/* Output. */
+};
+
+struct gsb_buffer {
+	u8 status;			/* GSB AttribRawProcess status. */
+	u8 len;				/* GSB AttribRawProcess length. */
+	union gsb_buffer_data data;
+} __packed;
+
+#define SAN_GSB_MAX_RQSX_PAYLOAD  (U8_MAX - 2 - sizeof(struct gsb_data_rqsx))
+#define SAN_GSB_MAX_RESPONSE	  (U8_MAX - 2 - sizeof(struct gsb_data_out))
+
+#define SAN_GSB_COMMAND		0
+
+enum san_gsb_request_cv {
+	SAN_GSB_REQUEST_CV_RQST = 0x01,
+	SAN_GSB_REQUEST_CV_ETWL = 0x02,
+	SAN_GSB_REQUEST_CV_RQSG = 0x03,
+};
+
+#define SAN_REQUEST_NUM_TRIES	5
+
+static acpi_status san_etwl(struct san_data *d, struct gsb_buffer *b)
+{
+	struct gsb_data_etwl *etwl = &b->data.etwl;
+
+	if (b->len < sizeof(struct gsb_data_etwl)) {
+		dev_err(d->dev, "invalid ETWL package (len = %d)\n", b->len);
+		return AE_OK;
+	}
+
+	dev_err(d->dev, "ETWL(%#04x, %#04x): %.*s\n", etwl->etw3, etwl->etw4,
+		(unsigned int)(b->len - sizeof(struct gsb_data_etwl)),
+		(char *)etwl->msg);
+
+	/* Indicate success. */
+	b->status = 0x00;
+	b->len = 0x00;
+
+	return AE_OK;
+}
+
+static
+struct gsb_data_rqsx *san_validate_rqsx(struct device *dev, const char *type,
+					struct gsb_buffer *b)
+{
+	struct gsb_data_rqsx *rqsx = &b->data.rqsx;
+
+	if (b->len < sizeof(struct gsb_data_rqsx)) {
+		dev_err(dev, "invalid %s package (len = %d)\n", type, b->len);
+		return NULL;
+	}
+
+	if (get_unaligned(&rqsx->cdl) != b->len - sizeof(struct gsb_data_rqsx)) {
+		dev_err(dev, "bogus %s package (len = %d, cdl = %d)\n",
+			type, b->len, get_unaligned(&rqsx->cdl));
+		return NULL;
+	}
+
+	if (get_unaligned(&rqsx->cdl) > SAN_GSB_MAX_RQSX_PAYLOAD) {
+		dev_err(dev, "payload for %s package too large (cdl = %d)\n",
+			type, get_unaligned(&rqsx->cdl));
+		return NULL;
+	}
+
+	return rqsx;
+}
+
+static void gsb_rqsx_response_error(struct gsb_buffer *gsb, int status)
+{
+	gsb->status = 0x00;
+	gsb->len = 0x02;
+	gsb->data.out.status = (u8)(-status);
+	gsb->data.out.len = 0x00;
+}
+
+static void gsb_rqsx_response_success(struct gsb_buffer *gsb, u8 *ptr, size_t len)
+{
+	gsb->status = 0x00;
+	gsb->len = len + 2;
+	gsb->data.out.status = 0x00;
+	gsb->data.out.len = len;
+
+	if (len)
+		memcpy(&gsb->data.out.pld[0], ptr, len);
+}
+
+static acpi_status san_rqst_fixup_suspended(struct san_data *d,
+					    struct ssam_request *rqst,
+					    struct gsb_buffer *gsb)
+{
+	if (rqst->target_category == SSAM_SSH_TC_BAS && rqst->command_id == 0x0D) {
+		u8 base_state = 1;
+
+		/* Base state quirk:
+		 * The base state may be queried from ACPI when the EC is still
+		 * suspended. In this case it will return '-EPERM'. This query
+		 * will only be triggered from the ACPI lid GPE interrupt, thus
+		 * we are either in laptop or studio mode (base status 0x01 or
+		 * 0x02). Furthermore, we will only get here if the device (and
+		 * EC) have been suspended.
+		 *
+		 * We now assume that the device is in laptop mode (0x01). This
+		 * has the drawback that it will wake the device when unfolding
+		 * it in studio mode, but it also allows us to avoid actively
+		 * waiting for the EC to wake up, which may incur a notable
+		 * delay.
+		 */
+
+		dev_dbg(d->dev, "rqst: fixup: base-state quirk\n");
+
+		gsb_rqsx_response_success(gsb, &base_state, sizeof(base_state));
+		return AE_OK;
+	}
+
+	gsb_rqsx_response_error(gsb, -ENXIO);
+	return AE_OK;
+}
+
+static acpi_status san_rqst(struct san_data *d, struct gsb_buffer *buffer)
+{
+	u8 rspbuf[SAN_GSB_MAX_RESPONSE];
+	struct gsb_data_rqsx *gsb_rqst;
+	struct ssam_request rqst;
+	struct ssam_response rsp;
+	int status = 0;
+
+	gsb_rqst = san_validate_rqsx(d->dev, "RQST", buffer);
+	if (!gsb_rqst)
+		return AE_OK;
+
+	rqst.target_category = gsb_rqst->tc;
+	rqst.target_id = gsb_rqst->tid;
+	rqst.command_id = gsb_rqst->cid;
+	rqst.instance_id = gsb_rqst->iid;
+	rqst.flags = gsb_rqst->snc ? SSAM_REQUEST_HAS_RESPONSE : 0;
+	rqst.length = get_unaligned(&gsb_rqst->cdl);
+	rqst.payload = &gsb_rqst->pld[0];
+
+	rsp.capacity = ARRAY_SIZE(rspbuf);
+	rsp.length = 0;
+	rsp.pointer = &rspbuf[0];
+
+	/* Handle suspended device. */
+	if (d->dev->power.is_suspended) {
+		dev_warn(d->dev, "rqst: device is suspended, not executing\n");
+		return san_rqst_fixup_suspended(d, &rqst, buffer);
+	}
+
+	status = __ssam_retry(ssam_request_sync_onstack, SAN_REQUEST_NUM_TRIES,
+			      d->ctrl, &rqst, &rsp, SAN_GSB_MAX_RQSX_PAYLOAD);
+
+	if (!status) {
+		gsb_rqsx_response_success(buffer, rsp.pointer, rsp.length);
+	} else {
+		dev_err(d->dev, "rqst: failed with error %d\n", status);
+		gsb_rqsx_response_error(buffer, status);
+	}
+
+	return AE_OK;
+}
+
+static acpi_status san_rqsg(struct san_data *d, struct gsb_buffer *buffer)
+{
+	struct gsb_data_rqsx *gsb_rqsg;
+	struct san_dgpu_event evt;
+	int status;
+
+	gsb_rqsg = san_validate_rqsx(d->dev, "RQSG", buffer);
+	if (!gsb_rqsg)
+		return AE_OK;
+
+	evt.category = gsb_rqsg->tc;
+	evt.target = gsb_rqsg->tid;
+	evt.command = gsb_rqsg->cid;
+	evt.instance = gsb_rqsg->iid;
+	evt.length = get_unaligned(&gsb_rqsg->cdl);
+	evt.payload = &gsb_rqsg->pld[0];
+
+	status = san_dgpu_notifier_call(&evt);
+	if (!status) {
+		gsb_rqsx_response_success(buffer, NULL, 0);
+	} else {
+		dev_err(d->dev, "rqsg: failed with error %d\n", status);
+		gsb_rqsx_response_error(buffer, status);
+	}
+
+	return AE_OK;
+}
+
+static acpi_status san_opreg_handler(u32 function, acpi_physical_address command,
+				     u32 bits, u64 *value64, void *opreg_context,
+				     void *region_context)
+{
+	struct san_data *d = to_san_data(opreg_context, info);
+	struct gsb_buffer *buffer = (struct gsb_buffer *)value64;
+	int accessor_type = (function & 0xFFFF0000) >> 16;
+
+	if (command != SAN_GSB_COMMAND) {
+		dev_warn(d->dev, "unsupported command: %#04llx\n", command);
+		return AE_OK;
+	}
+
+	if (accessor_type != ACPI_GSB_ACCESS_ATTRIB_RAW_PROCESS) {
+		dev_err(d->dev, "invalid access type: %#04x\n", accessor_type);
+		return AE_OK;
+	}
+
+	/* Buffer must have at least contain the command-value. */
+	if (buffer->len == 0) {
+		dev_err(d->dev, "request-package too small\n");
+		return AE_OK;
+	}
+
+	switch (buffer->data.in.cv) {
+	case SAN_GSB_REQUEST_CV_RQST:
+		return san_rqst(d, buffer);
+
+	case SAN_GSB_REQUEST_CV_ETWL:
+		return san_etwl(d, buffer);
+
+	case SAN_GSB_REQUEST_CV_RQSG:
+		return san_rqsg(d, buffer);
+
+	default:
+		dev_warn(d->dev, "unsupported SAN0 request (cv: %#04x)\n",
+			 buffer->data.in.cv);
+		return AE_OK;
+	}
+}
+
+
+/* -- Driver setup. --------------------------------------------------------- */
+
+static int san_events_register(struct platform_device *pdev)
+{
+	struct san_data *d = platform_get_drvdata(pdev);
+	int status;
+
+	d->nf_bat.base.priority = 1;
+	d->nf_bat.base.fn = san_evt_bat_nf;
+	d->nf_bat.event.reg = SSAM_EVENT_REGISTRY_SAM;
+	d->nf_bat.event.id.target_category = SSAM_SSH_TC_BAT;
+	d->nf_bat.event.id.instance = 0;
+	d->nf_bat.event.mask = SSAM_EVENT_MASK_TARGET;
+	d->nf_bat.event.flags = SSAM_EVENT_SEQUENCED;
+
+	d->nf_tmp.base.priority = 1;
+	d->nf_tmp.base.fn = san_evt_tmp_nf;
+	d->nf_tmp.event.reg = SSAM_EVENT_REGISTRY_SAM;
+	d->nf_tmp.event.id.target_category = SSAM_SSH_TC_TMP;
+	d->nf_tmp.event.id.instance = 0;
+	d->nf_tmp.event.mask = SSAM_EVENT_MASK_TARGET;
+	d->nf_tmp.event.flags = SSAM_EVENT_SEQUENCED;
+
+	status = ssam_notifier_register(d->ctrl, &d->nf_bat);
+	if (status)
+		return status;
+
+	status = ssam_notifier_register(d->ctrl, &d->nf_tmp);
+	if (status)
+		ssam_notifier_unregister(d->ctrl, &d->nf_bat);
+
+	return status;
+}
+
+static void san_events_unregister(struct platform_device *pdev)
+{
+	struct san_data *d = platform_get_drvdata(pdev);
+
+	ssam_notifier_unregister(d->ctrl, &d->nf_bat);
+	ssam_notifier_unregister(d->ctrl, &d->nf_tmp);
+}
+
+#define san_consumer_printk(level, dev, handle, fmt, ...)			\
+do {										\
+	char *path = "<error getting consumer path>";				\
+	struct acpi_buffer buffer = {						\
+		.length = ACPI_ALLOCATE_BUFFER,					\
+		.pointer = NULL,						\
+	};									\
+										\
+	if (ACPI_SUCCESS(acpi_get_name(handle, ACPI_FULL_PATHNAME, &buffer)))	\
+		path = buffer.pointer;						\
+										\
+	dev_##level(dev, "[%s]: " fmt, path, ##__VA_ARGS__);			\
+	kfree(buffer.pointer);							\
+} while (0)
+
+#define san_consumer_dbg(dev, handle, fmt, ...) \
+	san_consumer_printk(dbg, dev, handle, fmt, ##__VA_ARGS__)
+
+#define san_consumer_warn(dev, handle, fmt, ...) \
+	san_consumer_printk(warn, dev, handle, fmt, ##__VA_ARGS__)
+
+static bool is_san_consumer(struct platform_device *pdev, acpi_handle handle)
+{
+	struct acpi_handle_list dep_devices;
+	acpi_handle supplier = ACPI_HANDLE(&pdev->dev);
+	acpi_status status;
+	int i;
+
+	if (!acpi_has_method(handle, "_DEP"))
+		return false;
+
+	status = acpi_evaluate_reference(handle, "_DEP", NULL, &dep_devices);
+	if (ACPI_FAILURE(status)) {
+		san_consumer_dbg(&pdev->dev, handle, "failed to evaluate _DEP\n");
+		return false;
+	}
+
+	for (i = 0; i < dep_devices.count; i++) {
+		if (dep_devices.handles[i] == supplier)
+			return true;
+	}
+
+	return false;
+}
+
+static acpi_status san_consumer_setup(acpi_handle handle, u32 lvl,
+				      void *context, void **rv)
+{
+	const u32 flags = DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_SUPPLIER;
+	struct platform_device *pdev = context;
+	struct acpi_device *adev;
+	struct device_link *link;
+
+	if (!is_san_consumer(pdev, handle))
+		return AE_OK;
+
+	/* Ignore ACPI devices that are not present. */
+	if (acpi_bus_get_device(handle, &adev) != 0)
+		return AE_OK;
+
+	san_consumer_dbg(&pdev->dev, handle, "creating device link\n");
+
+	/* Try to set up device links, ignore but log errors. */
+	link = device_link_add(&adev->dev, &pdev->dev, flags);
+	if (!link) {
+		san_consumer_warn(&pdev->dev, handle, "failed to create device link\n");
+		return AE_OK;
+	}
+
+	return AE_OK;
+}
+
+static int san_consumer_links_setup(struct platform_device *pdev)
+{
+	acpi_status status;
+
+	status = acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
+				     ACPI_UINT32_MAX, san_consumer_setup, NULL,
+				     pdev, NULL);
+
+	return status ? -EFAULT : 0;
+}
+
+static int san_probe(struct platform_device *pdev)
+{
+	acpi_handle san = ACPI_HANDLE(&pdev->dev);
+	struct ssam_controller *ctrl;
+	struct san_data *data;
+	acpi_status astatus;
+	int status;
+
+	ctrl = ssam_client_bind(&pdev->dev);
+	if (IS_ERR(ctrl))
+		return PTR_ERR(ctrl) == -ENODEV ? -EPROBE_DEFER : PTR_ERR(ctrl);
+
+	status = san_consumer_links_setup(pdev);
+	if (status)
+		return status;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->dev = &pdev->dev;
+	data->ctrl = ctrl;
+
+	platform_set_drvdata(pdev, data);
+
+	astatus = acpi_install_address_space_handler(san, ACPI_ADR_SPACE_GSBUS,
+						     &san_opreg_handler, NULL,
+						     &data->info);
+	if (ACPI_FAILURE(astatus))
+		return -ENXIO;
+
+	status = san_events_register(pdev);
+	if (status)
+		goto err_enable_events;
+
+	status = san_set_rqsg_interface_device(&pdev->dev);
+	if (status)
+		goto err_install_dev;
+
+	acpi_walk_dep_device_list(san);
+	return 0;
+
+err_install_dev:
+	san_events_unregister(pdev);
+err_enable_events:
+	acpi_remove_address_space_handler(san, ACPI_ADR_SPACE_GSBUS,
+					  &san_opreg_handler);
+	return status;
+}
+
+static int san_remove(struct platform_device *pdev)
+{
+	acpi_handle san = ACPI_HANDLE(&pdev->dev);
+
+	san_set_rqsg_interface_device(NULL);
+	acpi_remove_address_space_handler(san, ACPI_ADR_SPACE_GSBUS,
+					  &san_opreg_handler);
+	san_events_unregister(pdev);
+
+	/*
+	 * We have unregistered our event sources. Now we need to ensure that
+	 * all delayed works they may have spawned are run to completion.
+	 */
+	flush_scheduled_work();
+
+	return 0;
+}
+
+static const struct acpi_device_id san_match[] = {
+	{ "MSHW0091" },
+	{ },
+};
+MODULE_DEVICE_TABLE(acpi, san_match);
+
+static struct platform_driver surface_acpi_notify = {
+	.probe = san_probe,
+	.remove = san_remove,
+	.driver = {
+		.name = "surface_acpi_notify",
+		.acpi_match_table = san_match,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+};
+module_platform_driver(surface_acpi_notify);
+
+MODULE_AUTHOR("Maximilian Luz <luzmaximilian@gmail.com>");
+MODULE_DESCRIPTION("Surface ACPI Notify driver for Surface System Aggregator Module");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/surface_acpi_notify.h b/include/linux/surface_acpi_notify.h
new file mode 100644
index 000000000000..8e3e86c7d78c
--- /dev/null
+++ b/include/linux/surface_acpi_notify.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Interface for Surface ACPI Notify (SAN) driver.
+ *
+ * Provides access to discrete GPU notifications sent from ACPI via the SAN
+ * driver, which are not handled by this driver directly.
+ *
+ * Copyright (C) 2019-2020 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _LINUX_SURFACE_ACPI_NOTIFY_H
+#define _LINUX_SURFACE_ACPI_NOTIFY_H
+
+#include <linux/notifier.h>
+#include <linux/types.h>
+
+/**
+ * struct san_dgpu_event - Discrete GPU ACPI event.
+ * @category: Category of the event.
+ * @target:   Target ID of the event source.
+ * @command:  Command ID of the event.
+ * @instance: Instance ID of the event source.
+ * @length:   Length of the event's payload data (in bytes).
+ * @payload:  Pointer to the event's payload data.
+ */
+struct san_dgpu_event {
+	u8 category;
+	u8 target;
+	u8 command;
+	u8 instance;
+	u16 length;
+	u8 *payload;
+};
+
+int san_client_link(struct device *client);
+int san_dgpu_notifier_register(struct notifier_block *nb);
+int san_dgpu_notifier_unregister(struct notifier_block *nb);
+
+#endif /* _LINUX_SURFACE_ACPI_NOTIFY_H */
