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, 184 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/touchwin.c b/drivers/input/touchscreen/touchwin.c
new file mode 100644
index 000000000..3ed33378d
--- /dev/null
+++ b/drivers/input/touchscreen/touchwin.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Touchwindow serial touchscreen driver
+ *
+ * Copyright (c) 2006 Rick Koch <n1gp@hotmail.com>
+ *
+ * Based on MicroTouch driver (drivers/input/touchscreen/mtouch.c)
+ * Copyright (c) 2004 Vojtech Pavlik
+ * and Dan Streetman <ddstreet@ieee.org>
+ */
+
+
+/*
+ * 2005/02/19 Rick Koch:
+ *   The Touchwindow I used is made by Edmark Corp. and
+ *   constantly outputs a stream of 0's unless it is touched.
+ *   It then outputs 3 bytes: X, Y, and a copy of Y.
+ */
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Touchwindow serial touchscreen driver"
+
+MODULE_AUTHOR("Rick Koch <n1gp@hotmail.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define TW_LENGTH 3
+
+#define TW_MIN_XC 0
+#define TW_MAX_XC 0xff
+#define TW_MIN_YC 0
+#define TW_MAX_YC 0xff
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct tw {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	int touched;
+	unsigned char data[TW_LENGTH];
+	char phys[32];
+};
+
+static irqreturn_t tw_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct tw *tw = serio_get_drvdata(serio);
+	struct input_dev *dev = tw->dev;
+
+	if (data) {		/* touch */
+		tw->touched = 1;
+		tw->data[tw->idx++] = data;
+		/* a full packet ends the accumulation, valid or not */
+		if (tw->idx == TW_LENGTH) {
+			/* report only if the two Y's are the same */
+			if (tw->data[1] == tw->data[2]) {
+				input_report_abs(dev, ABS_X, tw->data[0]);
+				input_report_abs(dev, ABS_Y, tw->data[1]);
+				input_report_key(dev, BTN_TOUCH, 1);
+				input_sync(dev);
+			}
+			tw->idx = 0;
+		}
+	} else if (tw->touched) {	/* untouch */
+		input_report_key(dev, BTN_TOUCH, 0);
+		input_sync(dev);
+		tw->idx = 0;
+		tw->touched = 0;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * tw_disconnect() is the opposite of tw_connect()
+ */
+
+static void tw_disconnect(struct serio *serio)
+{
+	struct tw *tw = serio_get_drvdata(serio);
+
+	input_get_device(tw->dev);
+	input_unregister_device(tw->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(tw->dev);
+	kfree(tw);
+}
+
+/*
+ * tw_connect() is the routine that is called when someone adds a
+ * new serio device that supports the Touchwin protocol and registers it as
+ * an input device.
+ */
+
+static int tw_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct tw *tw;
+	struct input_dev *input_dev;
+	int err;
+
+	tw = kzalloc_obj(*tw);
+	input_dev = input_allocate_device();
+	if (!tw || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	tw->serio = serio;
+	tw->dev = input_dev;
+	scnprintf(tw->phys, sizeof(tw->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Touchwindow Serial TouchScreen";
+	input_dev->phys = tw->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TOUCHWIN;
+	input_dev->id.product = 0;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
+	input_set_abs_params(tw->dev, ABS_X, TW_MIN_XC, TW_MAX_XC, 0, 0);
+	input_set_abs_params(tw->dev, ABS_Y, TW_MIN_YC, TW_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, tw);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(tw->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(tw);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id tw_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TOUCHWIN,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, tw_serio_ids);
+
+static struct serio_driver tw_drv = {
+	.driver		= {
+		.name	= "touchwin",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= tw_serio_ids,
+	.interrupt	= tw_interrupt,
+	.connect	= tw_connect,
+	.disconnect	= tw_disconnect,
+};
+
+module_serio_driver(tw_drv);