Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a', 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into HEADgrafted

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.

1 files changed, 154 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-max6902.c b/drivers/rtc/rtc-max6902.c
new file mode 100644
index 000000000..daaeb6fb6
--- /dev/null
+++ b/drivers/rtc/rtc-max6902.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* drivers/rtc/rtc-max6902.c
+ *
+ * Copyright (C) 2006 8D Technologies inc.
+ * Copyright (C) 2004 Compulab Ltd.
+ *
+ * Driver for MAX6902 spi RTC
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+
+#define MAX6902_REG_SECONDS		0x01
+#define MAX6902_REG_MINUTES		0x03
+#define MAX6902_REG_HOURS		0x05
+#define MAX6902_REG_DATE		0x07
+#define MAX6902_REG_MONTH		0x09
+#define MAX6902_REG_DAY			0x0B
+#define MAX6902_REG_YEAR		0x0D
+#define MAX6902_REG_CONTROL		0x0F
+#define MAX6902_REG_CENTURY		0x13
+
+static int max6902_set_reg(struct device *dev, unsigned char address,
+				unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	/* MSB must be '0' to write */
+	buf[0] = address & 0x7f;
+	buf[1] = data;
+
+	return spi_write_then_read(spi, buf, 2, NULL, 0);
+}
+
+static int max6902_get_reg(struct device *dev, unsigned char address,
+				unsigned char *data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+
+	/* Set MSB to indicate read */
+	*data = address | 0x80;
+
+	return spi_write_then_read(spi, data, 1, data, 1);
+}
+
+static int max6902_read_time(struct device *dev, struct rtc_time *dt)
+{
+	int err, century;
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[8];
+
+	buf[0] = 0xbf;	/* Burst read */
+
+	err = spi_write_then_read(spi, buf, 1, buf, 8);
+	if (err != 0)
+		return err;
+
+	/* The chip sends data in this order:
+	 * Seconds, Minutes, Hours, Date, Month, Day, Year */
+	dt->tm_sec	= bcd2bin(buf[0]);
+	dt->tm_min	= bcd2bin(buf[1]);
+	dt->tm_hour	= bcd2bin(buf[2]);
+	dt->tm_mday	= bcd2bin(buf[3]);
+	dt->tm_mon	= bcd2bin(buf[4]) - 1;
+	dt->tm_wday	= bcd2bin(buf[5]);
+	dt->tm_year	= bcd2bin(buf[6]);
+
+	/* Read century */
+	err = max6902_get_reg(dev, MAX6902_REG_CENTURY, &buf[0]);
+	if (err != 0)
+		return err;
+
+	century = bcd2bin(buf[0]) * 100;
+
+	dt->tm_year += century;
+	dt->tm_year -= 1900;
+
+	return 0;
+}
+
+static int max6902_set_time(struct device *dev, struct rtc_time *dt)
+{
+	dt->tm_year = dt->tm_year + 1900;
+
+	/* Remove write protection */
+	max6902_set_reg(dev, MAX6902_REG_CONTROL, 0);
+
+	max6902_set_reg(dev, MAX6902_REG_SECONDS, bin2bcd(dt->tm_sec));
+	max6902_set_reg(dev, MAX6902_REG_MINUTES, bin2bcd(dt->tm_min));
+	max6902_set_reg(dev, MAX6902_REG_HOURS, bin2bcd(dt->tm_hour));
+
+	max6902_set_reg(dev, MAX6902_REG_DATE, bin2bcd(dt->tm_mday));
+	max6902_set_reg(dev, MAX6902_REG_MONTH, bin2bcd(dt->tm_mon + 1));
+	max6902_set_reg(dev, MAX6902_REG_DAY, bin2bcd(dt->tm_wday));
+	max6902_set_reg(dev, MAX6902_REG_YEAR, bin2bcd(dt->tm_year % 100));
+	max6902_set_reg(dev, MAX6902_REG_CENTURY, bin2bcd(dt->tm_year / 100));
+
+	/* Compulab used a delay here. However, the datasheet
+	 * does not mention a delay being required anywhere... */
+	/* delay(2000); */
+
+	/* Write protect */
+	max6902_set_reg(dev, MAX6902_REG_CONTROL, 0x80);
+
+	return 0;
+}
+
+static const struct rtc_class_ops max6902_rtc_ops = {
+	.read_time	= max6902_read_time,
+	.set_time	= max6902_set_time,
+};
+
+static int max6902_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	unsigned char tmp;
+	int res;
+
+	spi->mode = SPI_MODE_3;
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	res = max6902_get_reg(&spi->dev, MAX6902_REG_SECONDS, &tmp);
+	if (res != 0)
+		return res;
+
+	rtc = devm_rtc_device_register(&spi->dev, "max6902",
+				&max6902_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	spi_set_drvdata(spi, rtc);
+	return 0;
+}
+
+static struct spi_driver max6902_driver = {
+	.driver = {
+		.name	= "rtc-max6902",
+	},
+	.probe	= max6902_probe,
+};
+
+module_spi_driver(max6902_driver);
+
+MODULE_DESCRIPTION("max6902 spi RTC driver");
+MODULE_AUTHOR("Raphael Assenat");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:rtc-max6902");