platform/surface: Add Surface ACPI Notify driver

The Surface ACPI Notify (SAN) device provides an ACPI interface to the
Surface Aggregator EC, specifically the Surface Serial Hub interface.
This interface allows EC requests to be made from ACPI code and can
convert a subset of EC events back to ACPI notifications.

Specifically, this interface provides a GenericSerialBus operation
region ACPI code can execute a request by writing the request command
data and payload to this operation region and reading back the
corresponding response via a write-then-read operation. Furthermore,
this interface provides a _DSM method to be called when certain events
from the EC have been received, essentially turning them into ACPI
notifications.

The driver provided in this commit essentially takes care of translating
the request data written to the operation region, executing the request,
waiting for it to finish, and finally writing and translating back the
response (if the request has one). Furthermore, this driver takes care
of enabling the events handled via ACPI _DSM calls. Lastly, this driver
also exposes an interface providing discrete GPU (dGPU) power-on
notifications on the Surface Book 2, which are also received via the
operation region interface (but not handled by the SAN driver directly),
making them accessible to other drivers (such as a dGPU hot-plug driver
that may be added later on).

On 5th and 6th generation Surface devices (Surface Pro 5/2017, Pro 6,
Book 2, Laptop 1 and 2), the SAN interface provides full battery and
thermal subsystem access, as well as other EC based functionality. On
those models, battery and thermal sensor devices are implemented as
standard ACPI devices of that type, however, forward ACPI calls to the
corresponding Surface Aggregator EC request via the SAN interface and
receive corresponding notifications (e.g. battery information change)
from it. This interface is therefore required to provide said
functionality on those devices.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20201221183959.1186143-10-luzmaximilian@gmail.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/platform/surface/Kconfig b/drivers/platform/surface/Kconfig
index 988b2de6b500..83b0a4c7b352 100644
--- a/drivers/platform/surface/Kconfig
+++ b/drivers/platform/surface/Kconfig
@@ -41,6 +41,25 @@ 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