platform/chrome: Add driver for ChromeOS privacy-screen

This adds the ACPI driver for the ChromeOS privacy screen that is
present on some chromeos devices.

Note that ideally, we'd want this privacy screen driver to be probed
BEFORE the drm probe in order to avoid a drm probe deferral:
https://hansdegoede.livejournal.com/25948.html

In practise, I found that ACPI drivers are bound to their devices AFTER
the drm probe on chromebooks. So on chromebooks with privacy-screen,
this patch along with the other one in this series results in a probe
deferral of about 250ms for i915 driver. However, it did not result in
any user noticeable delay of splash screen in my personal experience.

In future if this probe deferral turns out to be an issue, we can
consider turning this ACPI driver into something that is probed
earlier than the drm drivers.

Signed-off-by: Rajat Jain <rajatja@google.com>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Acked-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220107190208.95479-2-rajatja@google.com

drivers/platform/chrome/Kconfig

@@ -243,6 +243,17 @@ config CROS_USBPD_NOTIFY
 	  To compile this driver as a module, choose M here: the
 	  module will be called cros_usbpd_notify.
 
+config CHROMEOS_PRIVACY_SCREEN
+	tristate "ChromeOS Privacy Screen support"
+	depends on ACPI
+	depends on DRM
+	select DRM_PRIVACY_SCREEN
+	help
+	  This driver provides the support needed for the in-built electronic
+	  privacy screen that is present on some ChromeOS devices. When enabled,
+	  this should probably always be built into the kernel to avoid or
+	  minimize drm probe deferral.
+
 source "drivers/platform/chrome/wilco_ec/Kconfig"
 
 endif # CHROMEOS_PLATFORMS

drivers/platform/chrome/Makefile

@@ -4,6 +4,7 @@
 CFLAGS_cros_ec_trace.o:=		-I$(src)
 
 obj-$(CONFIG_CHROMEOS_LAPTOP)		+= chromeos_laptop.o
+obj-$(CONFIG_CHROMEOS_PRIVACY_SCREEN)	+= chromeos_privacy_screen.o
 obj-$(CONFIG_CHROMEOS_PSTORE)		+= chromeos_pstore.o
 obj-$(CONFIG_CHROMEOS_TBMC)		+= chromeos_tbmc.o
 obj-$(CONFIG_CROS_EC)			+= cros_ec.o

drivers/platform/chrome/chromeos_privacy_screen.c

@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ *  ChromeOS Privacy Screen support
+ *
+ * Copyright (C) 2022 Google LLC
+ *
+ * This is the Chromeos privacy screen provider, present on certain chromebooks,
+ * represented by a GOOG0010 device in the ACPI. This ACPI device, if present,
+ * will cause the i915 drm driver to probe defer until this driver registers
+ * the privacy-screen.
+ */
+
+#include <linux/acpi.h>
+#include <drm/drm_privacy_screen_driver.h>
+
+/*
+ * The DSM (Device Specific Method) constants below are the agreed API with
+ * the firmware team, on how to control privacy screen using ACPI methods.
+ */
+#define PRIV_SCRN_DSM_REVID		1	/* DSM version */
+#define PRIV_SCRN_DSM_FN_GET_STATUS	1	/* Get privacy screen status */
+#define PRIV_SCRN_DSM_FN_ENABLE		2	/* Enable privacy screen */
+#define PRIV_SCRN_DSM_FN_DISABLE	3	/* Disable privacy screen */
+
+static const guid_t chromeos_privacy_screen_dsm_guid =
+		    GUID_INIT(0xc7033113, 0x8720, 0x4ceb,
+			      0x90, 0x90, 0x9d, 0x52, 0xb3, 0xe5, 0x2d, 0x73);
+
+static void
+chromeos_privacy_screen_get_hw_state(struct drm_privacy_screen
+				     *drm_privacy_screen)
+{
+	union acpi_object *obj;
+	acpi_handle handle;
+	struct device *privacy_screen =
+		drm_privacy_screen_get_drvdata(drm_privacy_screen);
+
+	handle = acpi_device_handle(to_acpi_device(privacy_screen));
+	obj = acpi_evaluate_dsm(handle, &chromeos_privacy_screen_dsm_guid,
+				PRIV_SCRN_DSM_REVID,
+				PRIV_SCRN_DSM_FN_GET_STATUS, NULL);
+	if (!obj) {
+		dev_err(privacy_screen,
+			"_DSM failed to get privacy-screen state\n");
+		return;
+	}
+
+	if (obj->type != ACPI_TYPE_INTEGER)
+		dev_err(privacy_screen,
+			"Bad _DSM to get privacy-screen state\n");
+	else if (obj->integer.value == 1)
+		drm_privacy_screen->hw_state = drm_privacy_screen->sw_state =
+			PRIVACY_SCREEN_ENABLED;
+	else
+		drm_privacy_screen->hw_state = drm_privacy_screen->sw_state =
+			PRIVACY_SCREEN_DISABLED;
+
+	ACPI_FREE(obj);
+}
+
+static int
+chromeos_privacy_screen_set_sw_state(struct drm_privacy_screen
+				     *drm_privacy_screen,
+				     enum drm_privacy_screen_status state)
+{
+	union acpi_object *obj = NULL;
+	acpi_handle handle;
+	struct device *privacy_screen =
+		drm_privacy_screen_get_drvdata(drm_privacy_screen);
+
+	handle = acpi_device_handle(to_acpi_device(privacy_screen));
+
+	if (state == PRIVACY_SCREEN_DISABLED) {
+		obj = acpi_evaluate_dsm(handle,
+					&chromeos_privacy_screen_dsm_guid,
+					PRIV_SCRN_DSM_REVID,
+					PRIV_SCRN_DSM_FN_DISABLE, NULL);
+	} else if (state == PRIVACY_SCREEN_ENABLED) {
+		obj = acpi_evaluate_dsm(handle,
+					&chromeos_privacy_screen_dsm_guid,
+					PRIV_SCRN_DSM_REVID,
+					PRIV_SCRN_DSM_FN_ENABLE, NULL);
+	} else {
+		dev_err(privacy_screen,
+			"Bad attempt to set privacy-screen status to %u\n",
+			state);
+		return -EINVAL;
+	}
+
+	if (!obj) {
+		dev_err(privacy_screen,
+			"_DSM failed to set privacy-screen state\n");
+		return -EIO;
+	}
+
+	drm_privacy_screen->hw_state = drm_privacy_screen->sw_state = state;
+	ACPI_FREE(obj);
+	return 0;
+}
+
+static const struct drm_privacy_screen_ops chromeos_privacy_screen_ops = {
+	.get_hw_state = chromeos_privacy_screen_get_hw_state,
+	.set_sw_state = chromeos_privacy_screen_set_sw_state,
+};
+
+static int chromeos_privacy_screen_add(struct acpi_device *adev)
+{
+	struct drm_privacy_screen *drm_privacy_screen =
+		drm_privacy_screen_register(&adev->dev,
+					    &chromeos_privacy_screen_ops,
+					    &adev->dev);
+
+	if (IS_ERR(drm_privacy_screen)) {
+		dev_err(&adev->dev, "Error registering privacy-screen\n");
+		return PTR_ERR(drm_privacy_screen);
+	}
+
+	adev->driver_data = drm_privacy_screen;
+	dev_info(&adev->dev, "registered privacy-screen '%s'\n",
+		 dev_name(&drm_privacy_screen->dev));
+
+	return 0;
+}
+
+static int chromeos_privacy_screen_remove(struct acpi_device *adev)
+{
+	struct drm_privacy_screen *drm_privacy_screen =	acpi_driver_data(adev);
+
+	drm_privacy_screen_unregister(drm_privacy_screen);
+	return 0;
+}
+
+static const struct acpi_device_id chromeos_privacy_screen_device_ids[] = {
+	{"GOOG0010", 0}, /* Google's electronic privacy screen for eDP-1 */
+	{}
+};
+MODULE_DEVICE_TABLE(acpi, chromeos_privacy_screen_device_ids);
+
+static struct acpi_driver chromeos_privacy_screen_driver = {
+	.name = "chromeos_privacy_screen_driver",
+	.class = "ChromeOS",
+	.ids = chromeos_privacy_screen_device_ids,
+	.ops = {
+		.add = chromeos_privacy_screen_add,
+		.remove = chromeos_privacy_screen_remove,
+	},
+};
+
+module_acpi_driver(chromeos_privacy_screen_driver);
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("ChromeOS ACPI Privacy Screen driver");
+MODULE_AUTHOR("Rajat Jain <rajatja@google.com>");