sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 347 insertions, 0 deletions

diff --git a/drivers/video/backlight/lcd.c b/drivers/video/backlight/lcd.c
new file mode 100644
index 000000000..e918f5760
--- /dev/null
+++ b/drivers/video/backlight/lcd.c
@@ -0,0 +1,347 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * LCD Lowlevel Control Abstraction
+ *
+ * Copyright (C) 2003,2004 Hewlett-Packard Company
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/lcd.h>
+#include <linux/notifier.h>
+#include <linux/ctype.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+
+static DEFINE_MUTEX(lcd_dev_list_mutex);
+static LIST_HEAD(lcd_dev_list);
+
+static void lcd_notify_blank(struct lcd_device *ld, struct device *display_dev,
+			     int power)
+{
+	guard(mutex)(&ld->ops_lock);
+
+	if (!ld->ops || !ld->ops->set_power)
+		return;
+	if (ld->ops->controls_device && !ld->ops->controls_device(ld, display_dev))
+		return;
+
+	ld->ops->set_power(ld, power);
+}
+
+void lcd_notify_blank_all(struct device *display_dev, int power)
+{
+	struct lcd_device *ld;
+
+	guard(mutex)(&lcd_dev_list_mutex);
+
+	list_for_each_entry(ld, &lcd_dev_list, entry)
+		lcd_notify_blank(ld, display_dev, power);
+}
+EXPORT_SYMBOL(lcd_notify_blank_all);
+
+static void lcd_notify_mode_change(struct lcd_device *ld, struct device *display_dev,
+				   unsigned int width, unsigned int height)
+{
+	guard(mutex)(&ld->ops_lock);
+
+	if (!ld->ops || !ld->ops->set_mode)
+		return;
+	if (ld->ops->controls_device && !ld->ops->controls_device(ld, display_dev))
+		return;
+
+	ld->ops->set_mode(ld, width, height);
+}
+
+void lcd_notify_mode_change_all(struct device *display_dev,
+				unsigned int width, unsigned int height)
+{
+	struct lcd_device *ld;
+
+	guard(mutex)(&lcd_dev_list_mutex);
+
+	list_for_each_entry(ld, &lcd_dev_list, entry)
+		lcd_notify_mode_change(ld, display_dev, width, height);
+}
+EXPORT_SYMBOL(lcd_notify_mode_change_all);
+
+static ssize_t lcd_power_show(struct device *dev, struct device_attribute *attr,
+		char *buf)
+{
+	int rc;
+	struct lcd_device *ld = to_lcd_device(dev);
+
+	mutex_lock(&ld->ops_lock);
+	if (ld->ops && ld->ops->get_power)
+		rc = sprintf(buf, "%d\n", ld->ops->get_power(ld));
+	else
+		rc = -ENXIO;
+	mutex_unlock(&ld->ops_lock);
+
+	return rc;
+}
+
+static ssize_t lcd_power_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	int rc;
+	struct lcd_device *ld = to_lcd_device(dev);
+	unsigned long power;
+
+	rc = kstrtoul(buf, 0, &power);
+	if (rc)
+		return rc;
+
+	rc = -ENXIO;
+
+	mutex_lock(&ld->ops_lock);
+	if (ld->ops && ld->ops->set_power) {
+		pr_debug("set power to %lu\n", power);
+		ld->ops->set_power(ld, power);
+		rc = count;
+	}
+	mutex_unlock(&ld->ops_lock);
+
+	return rc;
+}
+static DEVICE_ATTR_RW(lcd_power);
+
+static ssize_t contrast_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	int rc = -ENXIO;
+	struct lcd_device *ld = to_lcd_device(dev);
+
+	mutex_lock(&ld->ops_lock);
+	if (ld->ops && ld->ops->get_contrast)
+		rc = sprintf(buf, "%d\n", ld->ops->get_contrast(ld));
+	mutex_unlock(&ld->ops_lock);
+
+	return rc;
+}
+
+static ssize_t contrast_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	int rc;
+	struct lcd_device *ld = to_lcd_device(dev);
+	unsigned long contrast;
+
+	rc = kstrtoul(buf, 0, &contrast);
+	if (rc)
+		return rc;
+
+	rc = -ENXIO;
+
+	mutex_lock(&ld->ops_lock);
+	if (ld->ops && ld->ops->set_contrast) {
+		pr_debug("set contrast to %lu\n", contrast);
+		ld->ops->set_contrast(ld, contrast);
+		rc = count;
+	}
+	mutex_unlock(&ld->ops_lock);
+
+	return rc;
+}
+static DEVICE_ATTR_RW(contrast);
+
+static ssize_t max_contrast_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct lcd_device *ld = to_lcd_device(dev);
+
+	return sprintf(buf, "%d\n", ld->props.max_contrast);
+}
+static DEVICE_ATTR_RO(max_contrast);
+
+static void lcd_device_release(struct device *dev)
+{
+	struct lcd_device *ld = to_lcd_device(dev);
+	kfree(ld);
+}
+
+static struct attribute *lcd_device_attrs[] = {
+	&dev_attr_lcd_power.attr,
+	&dev_attr_contrast.attr,
+	&dev_attr_max_contrast.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(lcd_device);
+
+static const struct class lcd_class = {
+	.name = "lcd",
+	.dev_groups = lcd_device_groups,
+};
+
+/**
+ * lcd_device_register - register a new object of lcd_device class.
+ * @name: the name of the new object(must be the same as the name of the
+ *   respective framebuffer device).
+ * @parent: pointer to the parent's struct device .
+ * @devdata: an optional pointer to be stored in the device. The
+ *   methods may retrieve it by using lcd_get_data(ld).
+ * @ops: the lcd operations structure.
+ *
+ * Creates and registers a new lcd device. Returns either an ERR_PTR()
+ * or a pointer to the newly allocated device.
+ */
+struct lcd_device *lcd_device_register(const char *name, struct device *parent,
+		void *devdata, const struct lcd_ops *ops)
+{
+	struct lcd_device *new_ld;
+	int rc;
+
+	pr_debug("lcd_device_register: name=%s\n", name);
+
+	new_ld = kzalloc_obj(struct lcd_device);
+	if (!new_ld)
+		return ERR_PTR(-ENOMEM);
+
+	mutex_init(&new_ld->ops_lock);
+	mutex_init(&new_ld->update_lock);
+
+	new_ld->dev.class = &lcd_class;
+	new_ld->dev.parent = parent;
+	new_ld->dev.release = lcd_device_release;
+	dev_set_name(&new_ld->dev, "%s", name);
+	dev_set_drvdata(&new_ld->dev, devdata);
+
+	new_ld->ops = ops;
+
+	rc = device_register(&new_ld->dev);
+	if (rc) {
+		put_device(&new_ld->dev);
+		return ERR_PTR(rc);
+	}
+
+	guard(mutex)(&lcd_dev_list_mutex);
+	list_add(&new_ld->entry, &lcd_dev_list);
+
+	return new_ld;
+}
+EXPORT_SYMBOL(lcd_device_register);
+
+/**
+ * lcd_device_unregister - unregisters a object of lcd_device class.
+ * @ld: the lcd device object to be unregistered and freed.
+ *
+ * Unregisters a previously registered via lcd_device_register object.
+ */
+void lcd_device_unregister(struct lcd_device *ld)
+{
+	if (!ld)
+		return;
+
+	guard(mutex)(&lcd_dev_list_mutex);
+	list_del(&ld->entry);
+
+	mutex_lock(&ld->ops_lock);
+	ld->ops = NULL;
+	mutex_unlock(&ld->ops_lock);
+
+	device_unregister(&ld->dev);
+}
+EXPORT_SYMBOL(lcd_device_unregister);
+
+static void devm_lcd_device_release(struct device *dev, void *res)
+{
+	struct lcd_device *lcd = *(struct lcd_device **)res;
+
+	lcd_device_unregister(lcd);
+}
+
+static int devm_lcd_device_match(struct device *dev, void *res, void *data)
+{
+	struct lcd_device **r = res;
+
+	return *r == data;
+}
+
+/**
+ * devm_lcd_device_register - resource managed lcd_device_register()
+ * @dev: the device to register
+ * @name: the name of the device
+ * @parent: a pointer to the parent device
+ * @devdata: an optional pointer to be stored for private driver use
+ * @ops: the lcd operations structure
+ *
+ * @return a struct lcd on success, or an ERR_PTR on error
+ *
+ * Managed lcd_device_register(). The lcd_device returned from this function
+ * are automatically freed on driver detach. See lcd_device_register()
+ * for more information.
+ */
+struct lcd_device *devm_lcd_device_register(struct device *dev,
+		const char *name, struct device *parent,
+		void *devdata, const struct lcd_ops *ops)
+{
+	struct lcd_device **ptr, *lcd;
+
+	ptr = devres_alloc(devm_lcd_device_release, sizeof(*ptr), GFP_KERNEL);
+	if (!ptr)
+		return ERR_PTR(-ENOMEM);
+
+	lcd = lcd_device_register(name, parent, devdata, ops);
+	if (!IS_ERR(lcd)) {
+		*ptr = lcd;
+		devres_add(dev, ptr);
+	} else {
+		devres_free(ptr);
+	}
+
+	return lcd;
+}
+EXPORT_SYMBOL(devm_lcd_device_register);
+
+/**
+ * devm_lcd_device_unregister - resource managed lcd_device_unregister()
+ * @dev: the device to unregister
+ * @ld: the lcd device to unregister
+ *
+ * Deallocated a lcd allocated with devm_lcd_device_register(). Normally
+ * this function will not need to be called and the resource management
+ * code will ensure that the resource is freed.
+ */
+void devm_lcd_device_unregister(struct device *dev, struct lcd_device *ld)
+{
+	int rc;
+
+	rc = devres_release(dev, devm_lcd_device_release,
+				devm_lcd_device_match, ld);
+	WARN_ON(rc);
+}
+EXPORT_SYMBOL(devm_lcd_device_unregister);
+
+
+static void __exit lcd_class_exit(void)
+{
+	class_unregister(&lcd_class);
+}
+
+static int __init lcd_class_init(void)
+{
+	int ret;
+
+	ret = class_register(&lcd_class);
+	if (ret) {
+		pr_warn("Unable to create backlight class; errno = %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+/*
+ * if this is compiled into the kernel, we need to ensure that the
+ * class is registered before users of the class try to register lcd's
+ */
+postcore_initcall(lcd_class_init);
+module_exit(lcd_class_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jamey Hicks <jamey.hicks@hp.com>, Andrew Zabolotny <zap@homelink.ru>");
+MODULE_DESCRIPTION("LCD Lowlevel Control Abstraction");