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, 89 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/tsc2005.c b/drivers/input/touchscreen/tsc2005.c
new file mode 100644
index 000000000..6fe8b41b3
--- /dev/null
+++ b/drivers/input/touchscreen/tsc2005.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * TSC2005 touchscreen driver
+ *
+ * Copyright (C) 2006-2010 Nokia Corporation
+ * Copyright (C) 2015 QWERTY Embedded Design
+ * Copyright (C) 2015 EMAC Inc.
+ *
+ * Based on original tsc2005.c by Lauri Leukkunen <lauri.leukkunen@nokia.com>
+ */
+
+#include <linux/input.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/spi/spi.h>
+#include <linux/regmap.h>
+#include "tsc200x-core.h"
+
+static const struct input_id tsc2005_input_id = {
+	.bustype = BUS_SPI,
+	.product = 2005,
+};
+
+static int tsc2005_cmd(struct device *dev, u8 cmd)
+{
+	u8 tx = TSC200X_CMD | TSC200X_CMD_12BIT | cmd;
+	struct spi_transfer xfer = {
+		.tx_buf         = &tx,
+		.len            = 1,
+		.bits_per_word  = 8,
+	};
+	struct spi_message msg;
+	struct spi_device *spi = to_spi_device(dev);
+	int error;
+
+	spi_message_init(&msg);
+	spi_message_add_tail(&xfer, &msg);
+
+	error = spi_sync(spi, &msg);
+	if (error) {
+		dev_err(dev, "%s: failed, command: %x, spi error: %d\n",
+			__func__, cmd, error);
+		return error;
+	}
+
+	return 0;
+}
+
+static int tsc2005_probe(struct spi_device *spi)
+{
+	int error;
+
+	spi->mode = SPI_MODE_0;
+	spi->bits_per_word = 8;
+	if (!spi->max_speed_hz)
+		spi->max_speed_hz = TSC2005_SPI_MAX_SPEED_HZ;
+
+	error = spi_setup(spi);
+	if (error)
+		return error;
+
+	return tsc200x_probe(&spi->dev, spi->irq, &tsc2005_input_id,
+			     devm_regmap_init_spi(spi, &tsc200x_regmap_config),
+			     tsc2005_cmd);
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id tsc2005_of_match[] = {
+	{ .compatible = "ti,tsc2005" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, tsc2005_of_match);
+#endif
+
+static struct spi_driver tsc2005_driver = {
+	.driver	= {
+		.name		= "tsc2005",
+		.dev_groups	= tsc200x_groups,
+		.of_match_table	= of_match_ptr(tsc2005_of_match),
+		.pm		= pm_sleep_ptr(&tsc200x_pm_ops),
+	},
+	.probe	= tsc2005_probe,
+};
+module_spi_driver(tsc2005_driver);
+
+MODULE_AUTHOR("Michael Welling <mwelling@ieee.org>");
+MODULE_DESCRIPTION("TSC2005 Touchscreen Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:tsc2005");