From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- drivers/rtc/rtc-max6916.c | 160 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 160 insertions(+) create mode 100644 drivers/rtc/rtc-max6916.c (limited to 'drivers/rtc/rtc-max6916.c') diff --git a/drivers/rtc/rtc-max6916.c b/drivers/rtc/rtc-max6916.c new file mode 100644 index 000000000..e72e768ab --- /dev/null +++ b/drivers/rtc/rtc-max6916.c @@ -0,0 +1,160 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* rtc-max6916.c + * + * Driver for MAXIM max6916 Low Current, SPI Compatible + * Real Time Clock + * + * Author : Venkat Prashanth B U + */ + +#include +#include +#include +#include +#include +#include +#include + +/* Registers in max6916 rtc */ + +#define MAX6916_SECONDS_REG 0x01 +#define MAX6916_MINUTES_REG 0x02 +#define MAX6916_HOURS_REG 0x03 +#define MAX6916_DATE_REG 0x04 +#define MAX6916_MONTH_REG 0x05 +#define MAX6916_DAY_REG 0x06 +#define MAX6916_YEAR_REG 0x07 +#define MAX6916_CONTROL_REG 0x08 +#define MAX6916_STATUS_REG 0x0C +#define MAX6916_CLOCK_BURST 0x3F + +static int max6916_read_reg(struct device *dev, unsigned char address, + unsigned char *data) +{ + struct spi_device *spi = to_spi_device(dev); + + *data = address | 0x80; + + return spi_write_then_read(spi, data, 1, data, 1); +} + +static int max6916_write_reg(struct device *dev, unsigned char address, + unsigned char data) +{ + struct spi_device *spi = to_spi_device(dev); + unsigned char buf[2]; + + buf[0] = address & 0x7F; + buf[1] = data; + + return spi_write_then_read(spi, buf, 2, NULL, 0); +} + +static int max6916_read_time(struct device *dev, struct rtc_time *dt) +{ + struct spi_device *spi = to_spi_device(dev); + int err; + unsigned char buf[8]; + + buf[0] = MAX6916_CLOCK_BURST | 0x80; + + err = spi_write_then_read(spi, buf, 1, buf, 8); + + if (err) + return err; + + dt->tm_sec = bcd2bin(buf[0]); + dt->tm_min = bcd2bin(buf[1]); + dt->tm_hour = bcd2bin(buf[2] & 0x3F); + dt->tm_mday = bcd2bin(buf[3]); + dt->tm_mon = bcd2bin(buf[4]) - 1; + dt->tm_wday = bcd2bin(buf[5]) - 1; + dt->tm_year = bcd2bin(buf[6]) + 100; + + return 0; +} + +static int max6916_set_time(struct device *dev, struct rtc_time *dt) +{ + struct spi_device *spi = to_spi_device(dev); + unsigned char buf[9]; + + if (dt->tm_year < 100 || dt->tm_year > 199) { + dev_err(&spi->dev, "Year must be between 2000 and 2099. It's %d.\n", + dt->tm_year + 1900); + return -EINVAL; + } + + buf[0] = MAX6916_CLOCK_BURST & 0x7F; + buf[1] = bin2bcd(dt->tm_sec); + buf[2] = bin2bcd(dt->tm_min); + buf[3] = (bin2bcd(dt->tm_hour) & 0X3F); + buf[4] = bin2bcd(dt->tm_mday); + buf[5] = bin2bcd(dt->tm_mon + 1); + buf[6] = bin2bcd(dt->tm_wday + 1); + buf[7] = bin2bcd(dt->tm_year % 100); + buf[8] = bin2bcd(0x00); + + /* write the rtc settings */ + return spi_write_then_read(spi, buf, 9, NULL, 0); +} + +static const struct rtc_class_ops max6916_rtc_ops = { + .read_time = max6916_read_time, + .set_time = max6916_set_time, +}; + +static int max6916_probe(struct spi_device *spi) +{ + struct rtc_device *rtc; + unsigned char data; + int res; + + /* spi setup with max6916 in mode 3 and bits per word as 8 */ + spi->mode = SPI_MODE_3; + spi->bits_per_word = 8; + spi_setup(spi); + + /* RTC Settings */ + res = max6916_read_reg(&spi->dev, MAX6916_SECONDS_REG, &data); + if (res) + return res; + + /* Disable the write protect of rtc */ + max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data); + data = data & ~(1 << 7); + max6916_write_reg(&spi->dev, MAX6916_CONTROL_REG, data); + + /*Enable oscillator,disable oscillator stop flag, glitch filter*/ + max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data); + data = data & 0x1B; + max6916_write_reg(&spi->dev, MAX6916_STATUS_REG, data); + + /* display the settings */ + max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data); + dev_info(&spi->dev, "MAX6916 RTC CTRL Reg = 0x%02x\n", data); + + max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data); + dev_info(&spi->dev, "MAX6916 RTC Status Reg = 0x%02x\n", data); + + rtc = devm_rtc_device_register(&spi->dev, "max6916", + &max6916_rtc_ops, THIS_MODULE); + if (IS_ERR(rtc)) + return PTR_ERR(rtc); + + spi_set_drvdata(spi, rtc); + + return 0; +} + +static struct spi_driver max6916_driver = { + .driver = { + .name = "max6916", + }, + .probe = max6916_probe, +}; +module_spi_driver(max6916_driver); + +MODULE_DESCRIPTION("MAX6916 SPI RTC DRIVER"); +MODULE_AUTHOR("Venkat Prashanth B U "); +MODULE_LICENSE("GPL v2"); -- cgit v1.3.1