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

Documentation/gpu/drm-kms-helpers.rst

@@ -435,3 +435,18 @@ Legacy CRTC/Modeset Helper Functions Reference
 
 .. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
    :export:
+
+Privacy-screen class
+====================
+
+.. kernel-doc:: drivers/gpu/drm/drm_privacy_screen.c
+   :doc: overview
+
+.. kernel-doc:: include/drm/drm_privacy_screen_driver.h
+   :internal:
+
+.. kernel-doc:: include/drm/drm_privacy_screen_machine.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_privacy_screen.c
+   :export:

MAINTAINERS

@@ -6422,6 +6422,14 @@ F:	drivers/gpu/drm/drm_panel.c
 F:	drivers/gpu/drm/panel/
 F:	include/drm/drm_panel.h
 
+DRM PRIVACY-SCREEN CLASS
+M:	Hans de Goede <hdegoede@redhat.com>
+L:	dri-devel@lists.freedesktop.org
+S:	Maintained
+T:	git git://anongit.freedesktop.org/drm/drm-misc
+F:	drivers/gpu/drm/drm_privacy_screen*
+F:	include/drm/drm_privacy_screen*
+
 DRM TTM SUBSYSTEM
 M:	Christian Koenig <christian.koenig@amd.com>
 M:	Huang Rui <ray.huang@amd.com>

drivers/gpu/drm/Kconfig

@@ -496,3 +496,7 @@ config DRM_PANEL_ORIENTATION_QUIRKS
 config DRM_LIB_RANDOM
 	bool
 	default n
+
+config DRM_PRIVACY_SCREEN
+	bool
+	default n

drivers/gpu/drm/Makefile

@@ -32,6 +32,7 @@ drm-$(CONFIG_OF) += drm_of.o
 drm-$(CONFIG_PCI) += drm_pci.o
 drm-$(CONFIG_DEBUG_FS) += drm_debugfs.o drm_debugfs_crc.o
 drm-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
+drm-$(CONFIG_DRM_PRIVACY_SCREEN) += drm_privacy_screen.o
 
 obj-$(CONFIG_DRM_DP_AUX_BUS) += drm_dp_aux_bus.o
 

drivers/gpu/drm/drm_drv.c

@@ -43,6 +43,7 @@
 #include <drm/drm_managed.h>
 #include <drm/drm_mode_object.h>
 #include <drm/drm_print.h>
+#include <drm/drm_privacy_screen_machine.h>
 
 #include "drm_crtc_internal.h"
 #include "drm_internal.h"
@@ -1029,6 +1030,7 @@ static const struct file_operations drm_stub_fops = {
 
 static void drm_core_exit(void)
 {
+	drm_privacy_screen_lookup_exit();
 	unregister_chrdev(DRM_MAJOR, "drm");
 	debugfs_remove(drm_debugfs_root);
 	drm_sysfs_destroy();
@@ -1056,6 +1058,8 @@ static int __init drm_core_init(void)
 	if (ret < 0)
 		goto error;
 
+	drm_privacy_screen_lookup_init();
+
 	drm_core_init_complete = true;
 
 	DRM_DEBUG("Initialized\n");

include/drm/drm_privacy_screen_consumer.h

+/* 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

include/drm/drm_privacy_screen_driver.h

+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright (C) 2020 Red Hat, Inc.
+ *
+ * Authors:
+ * Hans de Goede <hdegoede@redhat.com>
+ */
+
+#ifndef __DRM_PRIVACY_SCREEN_DRIVER_H__
+#define __DRM_PRIVACY_SCREEN_DRIVER_H__
+
+#include <linux/device.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <drm/drm_connector.h>
+
+struct drm_privacy_screen;
+
+/**
+ * struct drm_privacy_screen_ops - drm_privacy_screen operations
+ *
+ * Defines the operations which the privacy-screen class code may call.
+ * These functions should be implemented by the privacy-screen driver.
+ */
+struct drm_privacy_screen_ops {
+	/**
+	 * @set_sw_state: Called to request a change of the privacy-screen
+	 * state. The privacy-screen class code contains a check to avoid this
+	 * getting called when the hw_state reports the state is locked.
+	 * It is the driver's responsibility to update sw_state and hw_state.
+	 * This is always called with the drm_privacy_screen's lock held.
+	 */
+	int (*set_sw_state)(struct drm_privacy_screen *priv,
+			    enum drm_privacy_screen_status sw_state);
+	/**
+	 * @get_hw_state: Called to request that the driver gets the current
+	 * privacy-screen state from the hardware and then updates sw_state and
+	 * hw_state accordingly. This will be called by the core just before
+	 * the privacy-screen is registered in sysfs.
+	 */
+	void (*get_hw_state)(struct drm_privacy_screen *priv);
+};
+
+/**
+ * struct drm_privacy_screen - central privacy-screen structure
+ *
+ * Central privacy-screen structure, this contains the struct device used
+ * to register the screen in sysfs, the screen's state, ops, etc.
+ */
+struct drm_privacy_screen {
+	/** @dev: device used to register the privacy-screen in sysfs. */
+	struct device dev;
+	/** @lock: mutex protection all fields in this struct. */
+	struct mutex lock;
+	/** @list: privacy-screen devices list list-entry. */
+	struct list_head list;
+	/**
+	 * @ops: &struct drm_privacy_screen_ops for this privacy-screen.
+	 * This is NULL if the driver has unregistered the privacy-screen.
+	 */
+	const struct drm_privacy_screen_ops *ops;
+	/**
+	 * @sw_state: The privacy-screen's software state, see
+	 * :ref:`Standard Connector Properties<standard_connector_properties>`
+	 * for more info.
+	 */
+	enum drm_privacy_screen_status sw_state;
+	/**
+	 * @hw_state: The privacy-screen's hardware state, see
+	 * :ref:`Standard Connector Properties<standard_connector_properties>`
+	 * for more info.
+	 */
+	enum drm_privacy_screen_status hw_state;
+};
+
+struct drm_privacy_screen *drm_privacy_screen_register(
+	struct device *parent, const struct drm_privacy_screen_ops *ops);
+void drm_privacy_screen_unregister(struct drm_privacy_screen *priv);
+
+#endif

include/drm/drm_privacy_screen_machine.h

+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright (C) 2020 Red Hat, Inc.
+ *
+ * Authors:
+ * Hans de Goede <hdegoede@redhat.com>
+ */
+
+#ifndef __DRM_PRIVACY_SCREEN_MACHINE_H__
+#define __DRM_PRIVACY_SCREEN_MACHINE_H__
+
+#include <linux/list.h>
+
+/**
+ * struct drm_privacy_screen_lookup -  static privacy-screen lookup list entry
+ *
+ * Used for the static lookup-list for mapping privacy-screen consumer
+ * dev-connector pairs to a privacy-screen provider.
+ */
+struct drm_privacy_screen_lookup {
+	/** @list: Lookup list list-entry. */
+	struct list_head list;
+	/** @dev_id: Consumer device name or NULL to match all devices. */
+	const char *dev_id;
+	/** @con_id: Consumer connector name or NULL to match all connectors. */
+	const char *con_id;
+	/** @provider: dev_name() of the privacy_screen provider. */
+	const char *provider;
+};
+
+void drm_privacy_screen_lookup_add(struct drm_privacy_screen_lookup *lookup);
+void drm_privacy_screen_lookup_remove(struct drm_privacy_screen_lookup *lookup);
+
+static inline void drm_privacy_screen_lookup_init(void)
+{
+}
+static inline void drm_privacy_screen_lookup_exit(void)
+{
+}
+
+#endif