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, 156 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/ipaq-micro-ts.c b/drivers/input/touchscreen/ipaq-micro-ts.c
new file mode 100644
index 000000000..243e6465d
--- /dev/null
+++ b/drivers/input/touchscreen/ipaq-micro-ts.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * h3600 atmel micro companion support, touchscreen subdevice
+ * Author : Alessandro Gardich <gremlin@gremlin.it>
+ * Author : Dmitry Artamonow <mad_soft@inbox.ru>
+ * Author : Linus Walleij <linus.walleij@linaro.org>
+ */
+
+#include <asm/byteorder.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/pm.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/mfd/ipaq-micro.h>
+
+struct touchscreen_data {
+	struct input_dev *input;
+	struct ipaq_micro *micro;
+};
+
+static void micro_ts_receive(void *data, int len, unsigned char *msg)
+{
+	struct touchscreen_data *ts = data;
+
+	if (len == 4) {
+		input_report_abs(ts->input, ABS_X,
+				 be16_to_cpup((__be16 *) &msg[2]));
+		input_report_abs(ts->input, ABS_Y,
+				 be16_to_cpup((__be16 *) &msg[0]));
+		input_report_key(ts->input, BTN_TOUCH, 1);
+		input_sync(ts->input);
+	} else if (len == 0) {
+		input_report_abs(ts->input, ABS_X, 0);
+		input_report_abs(ts->input, ABS_Y, 0);
+		input_report_key(ts->input, BTN_TOUCH, 0);
+		input_sync(ts->input);
+	}
+}
+
+static void micro_ts_toggle_receive(struct touchscreen_data *ts, bool enable)
+{
+	struct ipaq_micro *micro = ts->micro;
+
+	guard(spinlock_irq)(&micro->lock);
+
+	if (enable) {
+		micro->ts = micro_ts_receive;
+		micro->ts_data = ts;
+	} else {
+		micro->ts = NULL;
+		micro->ts_data = NULL;
+	}
+}
+
+static int micro_ts_open(struct input_dev *input)
+{
+	struct touchscreen_data *ts = input_get_drvdata(input);
+
+	micro_ts_toggle_receive(ts, true);
+
+	return 0;
+}
+
+static void micro_ts_close(struct input_dev *input)
+{
+	struct touchscreen_data *ts = input_get_drvdata(input);
+
+	micro_ts_toggle_receive(ts, false);
+}
+
+static int micro_ts_probe(struct platform_device *pdev)
+{
+	struct ipaq_micro *micro = dev_get_drvdata(pdev->dev.parent);
+	struct touchscreen_data *ts;
+	int error;
+
+	ts = devm_kzalloc(&pdev->dev, sizeof(*ts), GFP_KERNEL);
+	if (!ts)
+		return -ENOMEM;
+
+	ts->micro = micro;
+
+	ts->input = devm_input_allocate_device(&pdev->dev);
+	if (!ts->input) {
+		dev_err(&pdev->dev, "failed to allocate input device\n");
+		return -ENOMEM;
+	}
+
+	ts->input->name = "ipaq micro ts";
+	ts->input->open = micro_ts_open;
+	ts->input->close = micro_ts_close;
+
+	input_set_drvdata(ts->input, ts);
+
+	input_set_capability(ts->input, EV_KEY, BTN_TOUCH);
+	input_set_capability(ts->input, EV_ABS, ABS_X);
+	input_set_capability(ts->input, EV_ABS, ABS_Y);
+	input_set_abs_params(ts->input, ABS_X, 0, 1023, 0, 0);
+	input_set_abs_params(ts->input, ABS_Y, 0, 1023, 0, 0);
+
+	error = input_register_device(ts->input);
+	if (error) {
+		dev_err(&pdev->dev, "error registering touch input\n");
+		return error;
+	}
+
+	platform_set_drvdata(pdev, ts);
+
+	dev_info(&pdev->dev, "iPAQ micro touchscreen\n");
+
+	return 0;
+}
+
+static int micro_ts_suspend(struct device *dev)
+{
+	struct touchscreen_data *ts = dev_get_drvdata(dev);
+
+	micro_ts_toggle_receive(ts, false);
+
+	return 0;
+}
+
+static int micro_ts_resume(struct device *dev)
+{
+	struct touchscreen_data *ts = dev_get_drvdata(dev);
+	struct input_dev *input = ts->input;
+
+	guard(mutex)(&input->mutex);
+
+	if (input_device_enabled(input))
+		micro_ts_toggle_receive(ts, true);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(micro_ts_dev_pm_ops,
+				micro_ts_suspend, micro_ts_resume);
+
+static struct platform_driver micro_ts_device_driver = {
+	.driver	= {
+		.name	= "ipaq-micro-ts",
+		.pm	= pm_sleep_ptr(&micro_ts_dev_pm_ops),
+	},
+	.probe	= micro_ts_probe,
+};
+module_platform_driver(micro_ts_device_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("driver for iPAQ Atmel micro touchscreen");
+MODULE_ALIAS("platform:ipaq-micro-ts");