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, 214 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/touchit213.c b/drivers/input/touchscreen/touchit213.c
new file mode 100644
index 000000000..6d4a1acf5
--- /dev/null
+++ b/drivers/input/touchscreen/touchit213.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Sahara TouchIT-213 serial touchscreen driver
+ *
+ * Copyright (c) 2007-2008 Claudio Nieder <private@claudio.ch>
+ *
+ * Based on Touchright driver (drivers/input/touchscreen/touchright.c)
+ * Copyright (c) 2006 Rick Koch <n1gp@hotmail.com>
+ * Copyright (c) 2004 Vojtech Pavlik
+ * and Dan Streetman <ddstreet@ieee.org>
+ */
+
+
+#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	"Sahara TouchIT-213 serial touchscreen driver"
+
+MODULE_AUTHOR("Claudio Nieder <private@claudio.ch>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+/*
+ * Data is received through COM1 at 9600bit/s,8bit,no parity in packets
+ * of 5 byte each.
+ *
+ *   +--------+   +--------+   +--------+   +--------+   +--------+
+ *   |1000000p|   |0xxxxxxx|   |0xxxxxxx|   |0yyyyyyy|   |0yyyyyyy|
+ *   +--------+   +--------+   +--------+   +--------+   +--------+
+ *                    MSB          LSB          MSB          LSB
+ *
+ * The value of p is 1 as long as the screen is touched and 0 when
+ * reporting the location where touching stopped, e.g. where the pen was
+ * lifted from the screen.
+ *
+ * When holding the screen in landscape mode as the BIOS text output is
+ * presented, x is the horizontal axis with values growing from left to
+ * right and y is the vertical axis with values growing from top to
+ * bottom.
+ *
+ * When holding the screen in portrait mode with the Sahara logo in its
+ * correct position, x ist the vertical axis with values growing from
+ * top to bottom and y is the horizontal axis with values growing from
+ * right to left.
+ */
+
+#define T213_FORMAT_TOUCH_BIT	0x01
+#define T213_FORMAT_STATUS_BYTE	0x80
+#define T213_FORMAT_STATUS_MASK	~T213_FORMAT_TOUCH_BIT
+
+/*
+ * On my Sahara Touch-IT 213 I have observed x values from 0 to 0x7f0
+ * and y values from 0x1d to 0x7e9, so the actual measurement is
+ * probably done with an 11 bit precision.
+ */
+#define T213_MIN_XC 0
+#define T213_MAX_XC 0x07ff
+#define T213_MIN_YC 0
+#define T213_MAX_YC 0x07ff
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct touchit213 {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char csum;
+	unsigned char data[5];
+	char phys[32];
+};
+
+static irqreturn_t touchit213_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct touchit213 *touchit213 = serio_get_drvdata(serio);
+	struct input_dev *dev = touchit213->dev;
+
+	touchit213->data[touchit213->idx] = data;
+
+	switch (touchit213->idx++) {
+	case 0:
+		if ((touchit213->data[0] & T213_FORMAT_STATUS_MASK) !=
+				T213_FORMAT_STATUS_BYTE) {
+			pr_debug("unsynchronized data: 0x%02x\n", data);
+			touchit213->idx = 0;
+		}
+		break;
+
+	case 4:
+		touchit213->idx = 0;
+		input_report_abs(dev, ABS_X,
+			(touchit213->data[1] << 7) | touchit213->data[2]);
+		input_report_abs(dev, ABS_Y,
+			(touchit213->data[3] << 7) | touchit213->data[4]);
+		input_report_key(dev, BTN_TOUCH,
+			touchit213->data[0] & T213_FORMAT_TOUCH_BIT);
+		input_sync(dev);
+		break;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * touchit213_disconnect() is the opposite of touchit213_connect()
+ */
+
+static void touchit213_disconnect(struct serio *serio)
+{
+	struct touchit213 *touchit213 = serio_get_drvdata(serio);
+
+	input_get_device(touchit213->dev);
+	input_unregister_device(touchit213->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(touchit213->dev);
+	kfree(touchit213);
+}
+
+/*
+ * touchit213_connect() is the routine that is called when someone adds a
+ * new serio device that supports the Touchright protocol and registers it as
+ * an input device.
+ */
+
+static int touchit213_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct touchit213 *touchit213;
+	struct input_dev *input_dev;
+	int err;
+
+	touchit213 = kzalloc_obj(*touchit213);
+	input_dev = input_allocate_device();
+	if (!touchit213 || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	touchit213->serio = serio;
+	touchit213->dev = input_dev;
+	scnprintf(touchit213->phys, sizeof(touchit213->phys),
+		  "%s/input0", serio->phys);
+
+	input_dev->name = "Sahara Touch-iT213 Serial TouchScreen";
+	input_dev->phys = touchit213->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TOUCHIT213;
+	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(touchit213->dev, ABS_X,
+			     T213_MIN_XC, T213_MAX_XC, 0, 0);
+	input_set_abs_params(touchit213->dev, ABS_Y,
+			     T213_MIN_YC, T213_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, touchit213);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(touchit213->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(touchit213);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id touchit213_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TOUCHIT213,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, touchit213_serio_ids);
+
+static struct serio_driver touchit213_drv = {
+	.driver		= {
+		.name	= "touchit213",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= touchit213_serio_ids,
+	.interrupt	= touchit213_interrupt,
+	.connect	= touchit213_connect,
+	.disconnect	= touchit213_disconnect,
+};
+
+module_serio_driver(touchit213_drv);