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, 329 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-hid-sensor-time.c b/drivers/rtc/rtc-hid-sensor-time.c
new file mode 100644
index 000000000..6228d0b24
--- /dev/null
+++ b/drivers/rtc/rtc-hid-sensor-time.c
@@ -0,0 +1,329 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * HID Sensor Time Driver
+ * Copyright (c) 2012, Alexander Holler.
+ */
+#include <linux/device.h>
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <linux/hid-sensor-hub.h>
+#include <linux/iio/iio.h>
+#include <linux/rtc.h>
+
+enum hid_time_channel {
+	CHANNEL_SCAN_INDEX_YEAR,
+	CHANNEL_SCAN_INDEX_MONTH,
+	CHANNEL_SCAN_INDEX_DAY,
+	CHANNEL_SCAN_INDEX_HOUR,
+	CHANNEL_SCAN_INDEX_MINUTE,
+	CHANNEL_SCAN_INDEX_SECOND,
+	TIME_RTC_CHANNEL_MAX,
+};
+
+struct hid_time_state {
+	struct hid_sensor_hub_callbacks callbacks;
+	struct hid_sensor_common common_attributes;
+	struct hid_sensor_hub_attribute_info info[TIME_RTC_CHANNEL_MAX];
+	struct rtc_time last_time;
+	spinlock_t lock_last_time;
+	struct completion comp_last_time;
+	struct rtc_time time_buf;
+	struct rtc_device *rtc;
+};
+
+static const u32 hid_time_addresses[TIME_RTC_CHANNEL_MAX] = {
+	HID_USAGE_SENSOR_TIME_YEAR,
+	HID_USAGE_SENSOR_TIME_MONTH,
+	HID_USAGE_SENSOR_TIME_DAY,
+	HID_USAGE_SENSOR_TIME_HOUR,
+	HID_USAGE_SENSOR_TIME_MINUTE,
+	HID_USAGE_SENSOR_TIME_SECOND,
+};
+
+/* Channel names for verbose error messages */
+static const char * const hid_time_channel_names[TIME_RTC_CHANNEL_MAX] = {
+	"year", "month", "day", "hour", "minute", "second",
+};
+
+/* Callback handler to send event after all samples are received and captured */
+static int hid_time_proc_event(struct hid_sensor_hub_device *hsdev,
+				unsigned usage_id, void *priv)
+{
+	unsigned long flags;
+	struct hid_time_state *time_state = platform_get_drvdata(priv);
+
+	spin_lock_irqsave(&time_state->lock_last_time, flags);
+	time_state->last_time = time_state->time_buf;
+	spin_unlock_irqrestore(&time_state->lock_last_time, flags);
+	complete(&time_state->comp_last_time);
+	return 0;
+}
+
+static u32 hid_time_value(size_t raw_len, char *raw_data)
+{
+	switch (raw_len) {
+	case 1:
+		return *(u8 *)raw_data;
+	case 2:
+		return *(u16 *)raw_data;
+	case 4:
+		return *(u32 *)raw_data;
+	default:
+		return (u32)(~0U); /* 0xff... or -1 to denote an error */
+	}
+}
+
+static int hid_time_capture_sample(struct hid_sensor_hub_device *hsdev,
+				unsigned usage_id, size_t raw_len,
+				char *raw_data, void *priv)
+{
+	struct hid_time_state *time_state = platform_get_drvdata(priv);
+	struct rtc_time *time_buf = &time_state->time_buf;
+
+	switch (usage_id) {
+	case HID_USAGE_SENSOR_TIME_YEAR:
+		/*
+		 * The draft for HID-sensors (HUTRR39) currently doesn't define
+		 * the range for the year attribute. Therefor we support
+		 * 8 bit (0-99) and 16 or 32 bits (full) as size for the year.
+		 */
+		if (raw_len == 1) {
+			time_buf->tm_year = *(u8 *)raw_data;
+			if (time_buf->tm_year < 70)
+				/* assume we are in 1970...2069 */
+				time_buf->tm_year += 100;
+		} else
+			time_buf->tm_year =
+				(int)hid_time_value(raw_len, raw_data)-1900;
+		break;
+	case HID_USAGE_SENSOR_TIME_MONTH:
+		/* sensors are sending the month as 1-12, we need 0-11 */
+		time_buf->tm_mon = (int)hid_time_value(raw_len, raw_data)-1;
+		break;
+	case HID_USAGE_SENSOR_TIME_DAY:
+		time_buf->tm_mday = (int)hid_time_value(raw_len, raw_data);
+		break;
+	case HID_USAGE_SENSOR_TIME_HOUR:
+		time_buf->tm_hour = (int)hid_time_value(raw_len, raw_data);
+		break;
+	case HID_USAGE_SENSOR_TIME_MINUTE:
+		time_buf->tm_min = (int)hid_time_value(raw_len, raw_data);
+		break;
+	case HID_USAGE_SENSOR_TIME_SECOND:
+		time_buf->tm_sec = (int)hid_time_value(raw_len, raw_data);
+		break;
+	default:
+		return -EINVAL;
+	}
+	return 0;
+}
+
+/* small helper, haven't found any other way */
+static const char *hid_time_attrib_name(u32 attrib_id)
+{
+	static const char unknown[] = "unknown";
+	unsigned i;
+
+	for (i = 0; i < TIME_RTC_CHANNEL_MAX; ++i) {
+		if (hid_time_addresses[i] == attrib_id)
+			return hid_time_channel_names[i];
+	}
+	return unknown; /* should never happen */
+}
+
+static int hid_time_parse_report(struct platform_device *pdev,
+				struct hid_sensor_hub_device *hsdev,
+				unsigned usage_id,
+				struct hid_time_state *time_state)
+{
+	int report_id, i;
+
+	for (i = 0; i < TIME_RTC_CHANNEL_MAX; ++i)
+		if (sensor_hub_input_get_attribute_info(hsdev,
+				HID_INPUT_REPORT, usage_id,
+				hid_time_addresses[i],
+				&time_state->info[i]) < 0)
+			return -EINVAL;
+	/* Check the (needed) attributes for sanity */
+	report_id = time_state->info[0].report_id;
+	if (report_id < 0) {
+		dev_err(&pdev->dev, "bad report ID!\n");
+		return -EINVAL;
+	}
+	for (i = 0; i < TIME_RTC_CHANNEL_MAX; ++i) {
+		if (time_state->info[i].report_id != report_id) {
+			dev_err(&pdev->dev,
+				"not all needed attributes inside the same report!\n");
+			return -EINVAL;
+		}
+		if (time_state->info[i].size == 3 ||
+				time_state->info[i].size > 4) {
+			dev_err(&pdev->dev,
+				"attribute '%s' not 8, 16 or 32 bits wide!\n",
+				hid_time_attrib_name(
+					time_state->info[i].attrib_id));
+			return -EINVAL;
+		}
+		if (time_state->info[i].units !=
+				HID_USAGE_SENSOR_UNITS_NOT_SPECIFIED &&
+				/* allow attribute seconds with unit seconds */
+				!(time_state->info[i].attrib_id ==
+				HID_USAGE_SENSOR_TIME_SECOND &&
+				time_state->info[i].units ==
+				HID_USAGE_SENSOR_UNITS_SECOND)) {
+			dev_err(&pdev->dev,
+				"attribute '%s' hasn't a unit of type 'none'!\n",
+				hid_time_attrib_name(
+					time_state->info[i].attrib_id));
+			return -EINVAL;
+		}
+		if (time_state->info[i].unit_expo) {
+			dev_err(&pdev->dev,
+				"attribute '%s' hasn't a unit exponent of 1!\n",
+				hid_time_attrib_name(
+					time_state->info[i].attrib_id));
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static int hid_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	unsigned long flags;
+	struct hid_time_state *time_state = dev_get_drvdata(dev);
+	int ret;
+
+	reinit_completion(&time_state->comp_last_time);
+	/* get a report with all values through requesting one value */
+	sensor_hub_input_attr_get_raw_value(time_state->common_attributes.hsdev,
+			HID_USAGE_SENSOR_TIME, hid_time_addresses[0],
+			time_state->info[0].report_id, SENSOR_HUB_SYNC, false);
+	/* wait for all values (event) */
+	ret = wait_for_completion_killable_timeout(
+			&time_state->comp_last_time, HZ*6);
+	if (ret > 0) {
+		/* no error */
+		spin_lock_irqsave(&time_state->lock_last_time, flags);
+		*tm = time_state->last_time;
+		spin_unlock_irqrestore(&time_state->lock_last_time, flags);
+		return 0;
+	}
+	if (!ret)
+		return -EIO; /* timeouted */
+	return ret; /* killed (-ERESTARTSYS) */
+}
+
+static const struct rtc_class_ops hid_time_rtc_ops = {
+	.read_time = hid_rtc_read_time,
+};
+
+static int hid_time_probe(struct platform_device *pdev)
+{
+	int ret = 0;
+	struct hid_sensor_hub_device *hsdev = dev_get_platdata(&pdev->dev);
+	struct hid_time_state *time_state = devm_kzalloc(&pdev->dev,
+		sizeof(struct hid_time_state), GFP_KERNEL);
+
+	if (time_state == NULL)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, time_state);
+
+	spin_lock_init(&time_state->lock_last_time);
+	init_completion(&time_state->comp_last_time);
+	time_state->common_attributes.hsdev = hsdev;
+	time_state->common_attributes.pdev = pdev;
+
+	ret = hid_sensor_parse_common_attributes(hsdev,
+				HID_USAGE_SENSOR_TIME,
+				&time_state->common_attributes,
+				NULL,
+				0);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to setup common attributes!\n");
+		return ret;
+	}
+
+	ret = hid_time_parse_report(pdev, hsdev, HID_USAGE_SENSOR_TIME,
+					time_state);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to setup attributes!\n");
+		return ret;
+	}
+
+	time_state->callbacks.send_event = hid_time_proc_event;
+	time_state->callbacks.capture_sample = hid_time_capture_sample;
+	time_state->callbacks.pdev = pdev;
+	ret = sensor_hub_register_callback(hsdev, HID_USAGE_SENSOR_TIME,
+					&time_state->callbacks);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "register callback failed!\n");
+		return ret;
+	}
+
+	ret = sensor_hub_device_open(hsdev);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to open sensor hub device!\n");
+		goto err_open;
+	}
+
+	/*
+	 * Enable HID input processing early in order to be able to read the
+	 * clock already in devm_rtc_device_register().
+	 */
+	hid_device_io_start(hsdev->hdev);
+
+	time_state->rtc = devm_rtc_device_register(&pdev->dev,
+					"hid-sensor-time", &hid_time_rtc_ops,
+					THIS_MODULE);
+
+	if (IS_ERR(time_state->rtc)) {
+		hid_device_io_stop(hsdev->hdev);
+		ret = PTR_ERR(time_state->rtc);
+		time_state->rtc = NULL;
+		dev_err(&pdev->dev, "rtc device register failed!\n");
+		goto err_rtc;
+	}
+
+	return ret;
+
+err_rtc:
+	sensor_hub_device_close(hsdev);
+err_open:
+	sensor_hub_remove_callback(hsdev, HID_USAGE_SENSOR_TIME);
+	return ret;
+}
+
+static void hid_time_remove(struct platform_device *pdev)
+{
+	struct hid_sensor_hub_device *hsdev = dev_get_platdata(&pdev->dev);
+
+	sensor_hub_device_close(hsdev);
+	sensor_hub_remove_callback(hsdev, HID_USAGE_SENSOR_TIME);
+}
+
+static const struct platform_device_id hid_time_ids[] = {
+	{
+		/* Format: HID-SENSOR-usage_id_in_hex_lowercase */
+		.name = "HID-SENSOR-2000a0",
+	},
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(platform, hid_time_ids);
+
+static struct platform_driver hid_time_platform_driver = {
+	.id_table = hid_time_ids,
+	.driver = {
+		.name	= KBUILD_MODNAME,
+	},
+	.probe		= hid_time_probe,
+	.remove		= hid_time_remove,
+};
+module_platform_driver(hid_time_platform_driver);
+
+MODULE_DESCRIPTION("HID Sensor Time");
+MODULE_AUTHOR("Alexander Holler <holler@ahsoftware.de>");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("IIO_HID");