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, 169 insertions, 0 deletions

diff --git a/drivers/mfd/ab8500-sysctrl.c b/drivers/mfd/ab8500-sysctrl.c
new file mode 100644
index 000000000..b6b44e2e3
--- /dev/null
+++ b/drivers/mfd/ab8500-sysctrl.c
@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AB8500 system control driver
+ *
+ * Copyright (C) ST-Ericsson SA 2010
+ * Author: Mattias Nilsson <mattias.i.nilsson@stericsson.com> for ST Ericsson.
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/export.h>
+#include <linux/platform_device.h>
+#include <linux/pm.h>
+#include <linux/reboot.h>
+#include <linux/signal.h>
+#include <linux/power_supply.h>
+#include <linux/mfd/abx500.h>
+#include <linux/mfd/abx500/ab8500.h>
+#include <linux/mfd/abx500/ab8500-sysctrl.h>
+
+/* RtcCtrl bits */
+#define AB8500_ALARM_MIN_LOW  0x08
+#define AB8500_ALARM_MIN_MID 0x09
+#define RTC_CTRL 0x0B
+#define RTC_ALARM_ENABLE 0x4
+
+static struct device *sysctrl_dev;
+
+static void ab8500_power_off(void)
+{
+	sigset_t old;
+	sigset_t all;
+	static const char * const pss[] = {"ab8500_ac", "ab8500_usb"};
+	int i;
+	bool charger_present = false;
+	union power_supply_propval val;
+	struct power_supply *psy;
+	int ret;
+
+	if (sysctrl_dev == NULL) {
+		pr_err("%s: sysctrl not initialized\n", __func__);
+		return;
+	}
+
+	/*
+	 * If we have a charger connected and we're powering off,
+	 * reboot into charge-only mode.
+	 */
+
+	for (i = 0; i < ARRAY_SIZE(pss); i++) {
+		psy = power_supply_get_by_name(pss[i]);
+		if (!psy)
+			continue;
+
+		ret = power_supply_get_property(psy, POWER_SUPPLY_PROP_ONLINE,
+				&val);
+		power_supply_put(psy);
+
+		if (!ret && val.intval) {
+			charger_present = true;
+			break;
+		}
+	}
+
+	if (!charger_present)
+		goto shutdown;
+
+	/* Check if battery is known */
+	psy = power_supply_get_by_name("ab8500_btemp");
+	if (psy) {
+		ret = power_supply_get_property(psy,
+				POWER_SUPPLY_PROP_TECHNOLOGY, &val);
+		if (!ret && val.intval != POWER_SUPPLY_TECHNOLOGY_UNKNOWN) {
+			pr_info("Charger '%s' is connected with known battery",
+				pss[i]);
+			pr_info(" - Rebooting.\n");
+			machine_restart("charging");
+		}
+		power_supply_put(psy);
+	}
+
+shutdown:
+	sigfillset(&all);
+
+	if (!sigprocmask(SIG_BLOCK, &all, &old)) {
+		(void)ab8500_sysctrl_set(AB8500_STW4500CTRL1,
+					 AB8500_STW4500CTRL1_SWOFF |
+					 AB8500_STW4500CTRL1_SWRESET4500N);
+		(void)sigprocmask(SIG_SETMASK, &old, NULL);
+	}
+}
+
+static inline bool valid_bank(u8 bank)
+{
+	return ((bank == AB8500_SYS_CTRL1_BLOCK) ||
+		(bank == AB8500_SYS_CTRL2_BLOCK));
+}
+
+int ab8500_sysctrl_read(u16 reg, u8 *value)
+{
+	u8 bank;
+
+	if (sysctrl_dev == NULL)
+		return -EPROBE_DEFER;
+
+	bank = (reg >> 8);
+	if (!valid_bank(bank))
+		return -EINVAL;
+
+	return abx500_get_register_interruptible(sysctrl_dev, bank,
+		(u8)(reg & 0xFF), value);
+}
+EXPORT_SYMBOL(ab8500_sysctrl_read);
+
+int ab8500_sysctrl_write(u16 reg, u8 mask, u8 value)
+{
+	u8 bank;
+
+	if (sysctrl_dev == NULL)
+		return -EPROBE_DEFER;
+
+	bank = (reg >> 8);
+	if (!valid_bank(bank)) {
+		pr_err("invalid bank\n");
+		return -EINVAL;
+	}
+
+	return abx500_mask_and_set_register_interruptible(sysctrl_dev, bank,
+		(u8)(reg & 0xFF), mask, value);
+}
+EXPORT_SYMBOL(ab8500_sysctrl_write);
+
+static int ab8500_sysctrl_probe(struct platform_device *pdev)
+{
+	sysctrl_dev = &pdev->dev;
+
+	if (!pm_power_off)
+		pm_power_off = ab8500_power_off;
+
+	return 0;
+}
+
+static void ab8500_sysctrl_remove(struct platform_device *pdev)
+{
+	sysctrl_dev = NULL;
+
+	if (pm_power_off == ab8500_power_off)
+		pm_power_off = NULL;
+}
+
+static const struct of_device_id ab8500_sysctrl_match[] = {
+	{ .compatible = "stericsson,ab8500-sysctrl", },
+	{}
+};
+
+static struct platform_driver ab8500_sysctrl_driver = {
+	.driver = {
+		.name = "ab8500-sysctrl",
+		.of_match_table = ab8500_sysctrl_match,
+	},
+	.probe = ab8500_sysctrl_probe,
+	.remove = ab8500_sysctrl_remove,
+};
+
+static int __init ab8500_sysctrl_init(void)
+{
+	return platform_driver_register(&ab8500_sysctrl_driver);
+}
+arch_initcall(ab8500_sysctrl_init);