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, 403 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_privacy_screen.c b/drivers/gpu/drm/drm_privacy_screen.c
new file mode 100644
index 000000000000..183a6011adf0
--- /dev/null
+++ b/drivers/gpu/drm/drm_privacy_screen.c
@@ -0,0 +1,403 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright (C) 2020 - 2021 Red Hat, Inc.
+ *
+ * Authors:
+ * Hans de Goede <hdegoede@redhat.com>
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <drm/drm_privacy_screen_machine.h>
+#include <drm/drm_privacy_screen_consumer.h>
+#include <drm/drm_privacy_screen_driver.h>
+#include "drm_internal.h"
+
+/**
+ * DOC: overview
+ *
+ * This class allows non KMS drivers, from e.g. drivers/platform/x86 to
+ * register a privacy-screen device, which the KMS drivers can then use
+ * to implement the standard privacy-screen properties, see
+ * :ref:`Standard Connector Properties<standard_connector_properties>`.
+ *
+ * KMS drivers using a privacy-screen class device are advised to use the
+ * drm_connector_attach_privacy_screen_provider() and
+ * drm_connector_update_privacy_screen() helpers for dealing with this.
+ */
+
+#define to_drm_privacy_screen(dev) \
+	container_of(dev, struct drm_privacy_screen, dev)
+
+static DEFINE_MUTEX(drm_privacy_screen_lookup_lock);
+static LIST_HEAD(drm_privacy_screen_lookup_list);
+
+static DEFINE_MUTEX(drm_privacy_screen_devs_lock);
+static LIST_HEAD(drm_privacy_screen_devs);
+
+/*** drm_privacy_screen_machine.h functions ***/
+
+/**
+ * drm_privacy_screen_lookup_add - add an entry to the static privacy-screen
+ *    lookup list
+ * @lookup: lookup list entry to add
+ *
+ * Add an entry to the static privacy-screen lookup list. Note the
+ * &struct list_head which is part of the &struct drm_privacy_screen_lookup
+ * gets added to a list owned by the privacy-screen core. So the passed in
+ * &struct drm_privacy_screen_lookup must not be free-ed until it is removed
+ * from the lookup list by calling drm_privacy_screen_lookup_remove().
+ */
+void drm_privacy_screen_lookup_add(struct drm_privacy_screen_lookup *lookup)
+{
+	mutex_lock(&drm_privacy_screen_lookup_lock);
+	list_add(&lookup->list, &drm_privacy_screen_lookup_list);
+	mutex_unlock(&drm_privacy_screen_lookup_lock);
+}
+EXPORT_SYMBOL(drm_privacy_screen_lookup_add);
+
+/**
+ * drm_privacy_screen_lookup_remove - remove an entry to the static
+ *    privacy-screen lookup list
+ * @lookup: lookup list entry to remove
+ *
+ * Remove an entry previously added with drm_privacy_screen_lookup_add()
+ * from the static privacy-screen lookup list.
+ */
+void drm_privacy_screen_lookup_remove(struct drm_privacy_screen_lookup *lookup)
+{
+	mutex_lock(&drm_privacy_screen_lookup_lock);
+	list_del(&lookup->list);
+	mutex_unlock(&drm_privacy_screen_lookup_lock);
+}
+EXPORT_SYMBOL(drm_privacy_screen_lookup_remove);
+
+/*** drm_privacy_screen_consumer.h functions ***/
+
+static struct drm_privacy_screen *drm_privacy_screen_get_by_name(
+	const char *name)
+{
+	struct drm_privacy_screen *priv;
+	struct device *dev = NULL;
+
+	mutex_lock(&drm_privacy_screen_devs_lock);
+
+	list_for_each_entry(priv, &drm_privacy_screen_devs, list) {
+		if (strcmp(dev_name(&priv->dev), name) == 0) {
+			dev = get_device(&priv->dev);
+			break;
+		}
+	}
+
+	mutex_unlock(&drm_privacy_screen_devs_lock);
+
+	return dev ? to_drm_privacy_screen(dev) : NULL;
+}
+
+/**
+ * drm_privacy_screen_get - get a privacy-screen provider
+ * @dev: consumer-device for which to get a privacy-screen provider
+ * @con_id: (video)connector name for which to get a privacy-screen provider
+ *
+ * Get a privacy-screen provider for a privacy-screen attached to the
+ * display described by the @dev and @con_id parameters.
+ *
+ * Return:
+ * * A pointer to a &struct drm_privacy_screen on success.
+ * * ERR_PTR(-ENODEV) if no matching privacy-screen is found
+ * * ERR_PTR(-EPROBE_DEFER) if there is a matching privacy-screen,
+ *                          but it has not been registered yet.
+ */
+struct drm_privacy_screen *drm_privacy_screen_get(struct device *dev,
+						  const char *con_id)
+{
+	const char *dev_id = dev ? dev_name(dev) : NULL;
+	struct drm_privacy_screen_lookup *l;
+	struct drm_privacy_screen *priv;
+	const char *provider = NULL;
+	int match, best = -1;
+
+	/*
+	 * For now we only support using a static lookup table, which is
+	 * populated by the drm_privacy_screen_arch_init() call. This should
+	 * be extended with device-tree / fw_node lookup when support is added
+	 * for device-tree using hardware with a privacy-screen.
+	 *
+	 * The lookup algorithm was shamelessly taken from the clock
+	 * framework:
+	 *
+	 * We do slightly fuzzy matching here:
+	 *  An entry with a NULL ID is assumed to be a wildcard.
+	 *  If an entry has a device ID, it must match
+	 *  If an entry has a connection ID, it must match
+	 * Then we take the most specific entry - with the following order
+	 * of precedence: dev+con > dev only > con only.
+	 */
+	mutex_lock(&drm_privacy_screen_lookup_lock);
+
+	list_for_each_entry(l, &drm_privacy_screen_lookup_list, list) {
+		match = 0;
+
+		if (l->dev_id) {
+			if (!dev_id || strcmp(l->dev_id, dev_id))
+				continue;
+
+			match += 2;
+		}
+
+		if (l->con_id) {
+			if (!con_id || strcmp(l->con_id, con_id))
+				continue;
+
+			match += 1;
+		}
+
+		if (match > best) {
+			provider = l->provider;
+			best = match;
+		}
+	}
+
+	mutex_unlock(&drm_privacy_screen_lookup_lock);
+
+	if (!provider)
+		return ERR_PTR(-ENODEV);
+
+	priv = drm_privacy_screen_get_by_name(provider);
+	if (!priv)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	return priv;
+}
+EXPORT_SYMBOL(drm_privacy_screen_get);
+
+/**
+ * drm_privacy_screen_put - release a privacy-screen reference
+ * @priv: privacy screen reference to release
+ *
+ * Release a privacy-screen provider reference gotten through
+ * drm_privacy_screen_get(). May be called with a NULL or ERR_PTR,
+ * in which case it is a no-op.
+ */
+void drm_privacy_screen_put(struct drm_privacy_screen *priv)
+{
+	if (IS_ERR_OR_NULL(priv))
+		return;
+
+	put_device(&priv->dev);
+}
+EXPORT_SYMBOL(drm_privacy_screen_put);
+
+/**
+ * drm_privacy_screen_set_sw_state - set a privacy-screen's sw-state
+ * @priv: privacy screen to set the sw-state for
+ * @sw_state: new sw-state value to set
+ *
+ * Set the sw-state of a privacy screen. If the privacy-screen is not
+ * in a locked hw-state, then the actual and hw-state of the privacy-screen
+ * will be immediately updated to the new value. If the privacy-screen is
+ * in a locked hw-state, then the new sw-state will be remembered as the
+ * requested state to put the privacy-screen in when it becomes unlocked.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int drm_privacy_screen_set_sw_state(struct drm_privacy_screen *priv,
+				    enum drm_privacy_screen_status sw_state)
+{
+	int ret = 0;
+
+	mutex_lock(&priv->lock);
+
+	if (!priv->ops) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	/*
+	 * As per the DRM connector properties documentation, setting the
+	 * sw_state while the hw_state is locked is allowed. In this case
+	 * it is a no-op other then storing the new sw_state so that it
+	 * can be honored when the state gets unlocked.
+	 * Also skip the set if the hw already is in the desired state.
+	 */
+	if (priv->hw_state >= PRIVACY_SCREEN_DISABLED_LOCKED ||
+	    priv->hw_state == sw_state) {
+		priv->sw_state = sw_state;
+		goto out;
+	}
+
+	ret = priv->ops->set_sw_state(priv, sw_state);
+out:
+	mutex_unlock(&priv->lock);
+	return ret;
+}
+EXPORT_SYMBOL(drm_privacy_screen_set_sw_state);
+
+/**
+ * drm_privacy_screen_get_state - get privacy-screen's current state
+ * @priv: privacy screen to get the state for
+ * @sw_state_ret: address where to store the privacy-screens current sw-state
+ * @hw_state_ret: address where to store the privacy-screens current hw-state
+ *
+ * Get the current state of a privacy-screen, both the sw-state and the
+ * hw-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)
+{
+	mutex_lock(&priv->lock);
+	*sw_state_ret = priv->sw_state;
+	*hw_state_ret = priv->hw_state;
+	mutex_unlock(&priv->lock);
+}
+EXPORT_SYMBOL(drm_privacy_screen_get_state);
+
+/*** drm_privacy_screen_driver.h functions ***/
+
+static ssize_t sw_state_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct drm_privacy_screen *priv = to_drm_privacy_screen(dev);
+	const char * const sw_state_names[] = {
+		"Disabled",
+		"Enabled",
+	};
+	ssize_t ret;
+
+	mutex_lock(&priv->lock);
+
+	if (!priv->ops)
+		ret = -ENODEV;
+	else if (WARN_ON(priv->sw_state >= ARRAY_SIZE(sw_state_names)))
+		ret = -ENXIO;
+	else
+		ret = sprintf(buf, "%s\n", sw_state_names[priv->sw_state]);
+
+	mutex_unlock(&priv->lock);
+	return ret;
+}
+/*
+ * RO: Do not allow setting the sw_state through sysfs, this MUST be done
+ * through the drm_properties on the drm_connector.
+ */
+static DEVICE_ATTR_RO(sw_state);
+
+static ssize_t hw_state_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct drm_privacy_screen *priv = to_drm_privacy_screen(dev);
+	const char * const hw_state_names[] = {
+		"Disabled",
+		"Enabled",
+		"Disabled, locked",
+		"Enabled, locked",
+	};
+	ssize_t ret;
+
+	mutex_lock(&priv->lock);
+
+	if (!priv->ops)
+		ret = -ENODEV;
+	else if (WARN_ON(priv->hw_state >= ARRAY_SIZE(hw_state_names)))
+		ret = -ENXIO;
+	else
+		ret = sprintf(buf, "%s\n", hw_state_names[priv->hw_state]);
+
+	mutex_unlock(&priv->lock);
+	return ret;
+}
+static DEVICE_ATTR_RO(hw_state);
+
+static struct attribute *drm_privacy_screen_attrs[] = {
+	&dev_attr_sw_state.attr,
+	&dev_attr_hw_state.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(drm_privacy_screen);
+
+static struct device_type drm_privacy_screen_type = {
+	.name = "privacy_screen",
+	.groups = drm_privacy_screen_groups,
+};
+
+static void drm_privacy_screen_device_release(struct device *dev)
+{
+	struct drm_privacy_screen *priv = to_drm_privacy_screen(dev);
+
+	kfree(priv);
+}
+
+/**
+ * drm_privacy_screen_register - register a privacy-screen
+ * @parent: parent-device for the privacy-screen
+ * @ops: &struct drm_privacy_screen_ops pointer with ops for the privacy-screen
+ *
+ * Create and register a privacy-screen.
+ *
+ * Return:
+ * * A pointer to the created privacy-screen on success.
+ * * An ERR_PTR(errno) on failure.
+ */
+struct drm_privacy_screen *drm_privacy_screen_register(
+	struct device *parent, const struct drm_privacy_screen_ops *ops)
+{
+	struct drm_privacy_screen *priv;
+	int ret;
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return ERR_PTR(-ENOMEM);
+
+	mutex_init(&priv->lock);
+
+	priv->dev.class = drm_class;
+	priv->dev.type = &drm_privacy_screen_type;
+	priv->dev.parent = parent;
+	priv->dev.release = drm_privacy_screen_device_release;
+	dev_set_name(&priv->dev, "privacy_screen-%s", dev_name(parent));
+	priv->ops = ops;
+
+	priv->ops->get_hw_state(priv);
+
+	ret = device_register(&priv->dev);
+	if (ret) {
+		put_device(&priv->dev);
+		return ERR_PTR(ret);
+	}
+
+	mutex_lock(&drm_privacy_screen_devs_lock);
+	list_add(&priv->list, &drm_privacy_screen_devs);
+	mutex_unlock(&drm_privacy_screen_devs_lock);
+
+	return priv;
+}
+EXPORT_SYMBOL(drm_privacy_screen_register);
+
+/**
+ * drm_privacy_screen_unregister - unregister privacy-screen
+ * @priv: privacy-screen to unregister
+ *
+ * Unregister a privacy-screen registered with drm_privacy_screen_register().
+ * May be called with a NULL or ERR_PTR, in which case it is a no-op.
+ */
+void drm_privacy_screen_unregister(struct drm_privacy_screen *priv)
+{
+	if (IS_ERR_OR_NULL(priv))
+		return;
+
+	mutex_lock(&drm_privacy_screen_devs_lock);
+	list_del(&priv->list);
+	mutex_unlock(&drm_privacy_screen_devs_lock);
+
+	mutex_lock(&priv->lock);
+	priv->ops = NULL;
+	mutex_unlock(&priv->lock);
+
+	device_unregister(&priv->dev);
+}
+EXPORT_SYMBOL(drm_privacy_screen_unregister);