drm: Add privacy-screen class (v4)

On some new laptops the LCD panel has a builtin electronic privacy-screen.
We want to export this functionality as a property on the drm connector
object. But often this functionality is not exposed on the GPU but on some
other (ACPI) device.

This commit adds a privacy-screen class allowing the driver for these
other devices to register themselves as a privacy-screen provider; and
allowing the drm/kms code to get a privacy-screen provider associated
with a specific GPU/connector combo.

Changes in v2:
- Make CONFIG_DRM_PRIVACY_SCREEN a bool which controls if the drm_privacy
  code gets built as part of the main drm module rather then making it
  a tristate which builds its own module.
- Add a #if IS_ENABLED(CONFIG_DRM_PRIVACY_SCREEN) check to
  drm_privacy_screen_consumer.h and define stubs when the check fails.
  Together these 2 changes fix several dependency issues.
- Remove module related code now that this is part of the main drm.ko
- Use drm_class as class for the privacy-screen devices instead of
  adding a separate class for this

Changes in v3:
- Make the static inline drm_privacy_screen_get_state() stub set sw_state
  and hw_state to PRIVACY_SCREEN_DISABLED to squelch an uninitialized
  variable warning when CONFIG_DRM_PRIVICAY_SCREEN is not set

Changes in v4:
- Make drm_privacy_screen_set_sw_state() skip calling out to the hw if
  hw_state == new_sw_state

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211005202322.700909-3-hdegoede@redhat.com

1 files changed, 50 insertions, 0 deletions

diff --git a/include/drm/drm_privacy_screen_consumer.h b/include/drm/drm_privacy_screen_consumer.h
new file mode 100644
index 000000000000..0cbd23b0453d
--- /dev/null
+++ b/include/drm/drm_privacy_screen_consumer.h
@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright (C) 2020 Red Hat, Inc.
+ *
+ * Authors:
+ * Hans de Goede <hdegoede@redhat.com>
+ */
+
+#ifndef __DRM_PRIVACY_SCREEN_CONSUMER_H__
+#define __DRM_PRIVACY_SCREEN_CONSUMER_H__
+
+#include <linux/device.h>
+#include <drm/drm_connector.h>
+
+struct drm_privacy_screen;
+
+#if IS_ENABLED(CONFIG_DRM_PRIVACY_SCREEN)
+struct drm_privacy_screen *drm_privacy_screen_get(struct device *dev,
+						  const char *con_id);
+void drm_privacy_screen_put(struct drm_privacy_screen *priv);
+
+int drm_privacy_screen_set_sw_state(struct drm_privacy_screen *priv,
+				    enum drm_privacy_screen_status sw_state);
+void drm_privacy_screen_get_state(struct drm_privacy_screen *priv,
+				  enum drm_privacy_screen_status *sw_state_ret,
+				  enum drm_privacy_screen_status *hw_state_ret);
+#else
+static inline struct drm_privacy_screen *drm_privacy_screen_get(struct device *dev,
+								const char *con_id)
+{
+	return ERR_PTR(-ENODEV);
+}
+static inline void drm_privacy_screen_put(struct drm_privacy_screen *priv)
+{
+}
+static inline int drm_privacy_screen_set_sw_state(struct drm_privacy_screen *priv,
+						  enum drm_privacy_screen_status sw_state)
+{
+	return -ENODEV;
+}
+static inline void drm_privacy_screen_get_state(struct drm_privacy_screen *priv,
+						enum drm_privacy_screen_status *sw_state_ret,
+						enum drm_privacy_screen_status *hw_state_ret)
+{
+	*sw_state_ret = PRIVACY_SCREEN_DISABLED;
+	*hw_state_ret = PRIVACY_SCREEN_DISABLED;
+}
+#endif
+
+#endif