kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 470 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-tps65910.c b/drivers/rtc/rtc-tps65910.c
new file mode 100644
index 000000000..284aa2f03
--- /dev/null
+++ b/drivers/rtc/rtc-tps65910.c
@@ -0,0 +1,470 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * rtc-tps65910.c -- TPS65910 Real Time Clock interface
+ *
+ * Copyright (c) 2012, NVIDIA CORPORATION.  All rights reserved.
+ * Author: Venu Byravarasu <vbyravarasu@nvidia.com>
+ *
+ * Based on original TI driver rtc-twl.c
+ *   Copyright (C) 2007 MontaVista Software, Inc
+ *   Author: Alexandre Rusev <source@mvista.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+#include <linux/math64.h>
+#include <linux/property.h>
+#include <linux/platform_device.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/tps65910.h>
+
+struct tps65910_rtc {
+	struct rtc_device	*rtc;
+	int irq;
+};
+
+/* Total number of RTC registers needed to set time*/
+#define NUM_TIME_REGS	(TPS65910_YEARS - TPS65910_SECONDS + 1)
+
+/* Total number of RTC registers needed to set compensation registers */
+#define NUM_COMP_REGS	(TPS65910_RTC_COMP_MSB - TPS65910_RTC_COMP_LSB + 1)
+
+/* Min and max values supported with 'offset' interface (swapped sign) */
+#define MIN_OFFSET	(-277761)
+#define MAX_OFFSET	(277778)
+
+/* Number of ticks per hour */
+#define TICKS_PER_HOUR	(32768 * 3600)
+
+/* Multiplier for ppb conversions */
+#define PPB_MULT	(1000000000LL)
+
+static int tps65910_rtc_alarm_irq_enable(struct device *dev,
+					 unsigned int enabled)
+{
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	u8 val = 0;
+
+	if (enabled)
+		val = TPS65910_RTC_INTERRUPTS_IT_ALARM;
+
+	return regmap_write(tps->regmap, TPS65910_RTC_INTERRUPTS, val);
+}
+
+/*
+ * Gets current tps65910 RTC time and date parameters.
+ *
+ * The RTC's time/alarm representation is not what gmtime(3) requires
+ * Linux to use:
+ *
+ *  - Months are 1..12 vs Linux 0-11
+ *  - Years are 0..99 vs Linux 1900..N (we assume 21st century)
+ */
+static int tps65910_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	unsigned char rtc_data[NUM_TIME_REGS];
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	int ret;
+
+	/* Copy RTC counting registers to static registers or latches */
+	ret = regmap_update_bits(tps->regmap, TPS65910_RTC_CTRL,
+		TPS65910_RTC_CTRL_GET_TIME, TPS65910_RTC_CTRL_GET_TIME);
+	if (ret < 0) {
+		dev_err(dev, "RTC CTRL reg update failed with err:%d\n", ret);
+		return ret;
+	}
+
+	ret = regmap_bulk_read(tps->regmap, TPS65910_SECONDS, rtc_data,
+		NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "reading from RTC failed with err:%d\n", ret);
+		return ret;
+	}
+
+	tm->tm_sec = bcd2bin(rtc_data[0]);
+	tm->tm_min = bcd2bin(rtc_data[1]);
+	tm->tm_hour = bcd2bin(rtc_data[2]);
+	tm->tm_mday = bcd2bin(rtc_data[3]);
+	tm->tm_mon = bcd2bin(rtc_data[4]) - 1;
+	tm->tm_year = bcd2bin(rtc_data[5]) + 100;
+
+	return ret;
+}
+
+static int tps65910_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	unsigned char rtc_data[NUM_TIME_REGS];
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	int ret;
+
+	rtc_data[0] = bin2bcd(tm->tm_sec);
+	rtc_data[1] = bin2bcd(tm->tm_min);
+	rtc_data[2] = bin2bcd(tm->tm_hour);
+	rtc_data[3] = bin2bcd(tm->tm_mday);
+	rtc_data[4] = bin2bcd(tm->tm_mon + 1);
+	rtc_data[5] = bin2bcd(tm->tm_year - 100);
+
+	/* Stop RTC while updating the RTC time registers */
+	ret = regmap_update_bits(tps->regmap, TPS65910_RTC_CTRL,
+		TPS65910_RTC_CTRL_STOP_RTC, 0);
+	if (ret < 0) {
+		dev_err(dev, "RTC stop failed with err:%d\n", ret);
+		return ret;
+	}
+
+	/* update all the time registers in one shot */
+	ret = regmap_bulk_write(tps->regmap, TPS65910_SECONDS, rtc_data,
+		NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "rtc_set_time error %d\n", ret);
+		return ret;
+	}
+
+	/* Start back RTC */
+	ret = regmap_update_bits(tps->regmap, TPS65910_RTC_CTRL,
+		TPS65910_RTC_CTRL_STOP_RTC, 1);
+	if (ret < 0)
+		dev_err(dev, "RTC start failed with err:%d\n", ret);
+
+	return ret;
+}
+
+/*
+ * Gets current tps65910 RTC alarm time.
+ */
+static int tps65910_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	unsigned char alarm_data[NUM_TIME_REGS];
+	u32 int_val;
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	int ret;
+
+	ret = regmap_bulk_read(tps->regmap, TPS65910_ALARM_SECONDS, alarm_data,
+		NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "rtc_read_alarm error %d\n", ret);
+		return ret;
+	}
+
+	alm->time.tm_sec = bcd2bin(alarm_data[0]);
+	alm->time.tm_min = bcd2bin(alarm_data[1]);
+	alm->time.tm_hour = bcd2bin(alarm_data[2]);
+	alm->time.tm_mday = bcd2bin(alarm_data[3]);
+	alm->time.tm_mon = bcd2bin(alarm_data[4]) - 1;
+	alm->time.tm_year = bcd2bin(alarm_data[5]) + 100;
+
+	ret = regmap_read(tps->regmap, TPS65910_RTC_INTERRUPTS, &int_val);
+	if (ret < 0)
+		return ret;
+
+	if (int_val & TPS65910_RTC_INTERRUPTS_IT_ALARM)
+		alm->enabled = 1;
+
+	return ret;
+}
+
+static int tps65910_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	unsigned char alarm_data[NUM_TIME_REGS];
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	int ret;
+
+	ret = tps65910_rtc_alarm_irq_enable(dev, 0);
+	if (ret)
+		return ret;
+
+	alarm_data[0] = bin2bcd(alm->time.tm_sec);
+	alarm_data[1] = bin2bcd(alm->time.tm_min);
+	alarm_data[2] = bin2bcd(alm->time.tm_hour);
+	alarm_data[3] = bin2bcd(alm->time.tm_mday);
+	alarm_data[4] = bin2bcd(alm->time.tm_mon + 1);
+	alarm_data[5] = bin2bcd(alm->time.tm_year - 100);
+
+	/* update all the alarm registers in one shot */
+	ret = regmap_bulk_write(tps->regmap, TPS65910_ALARM_SECONDS,
+		alarm_data, NUM_TIME_REGS);
+	if (ret) {
+		dev_err(dev, "rtc_set_alarm error %d\n", ret);
+		return ret;
+	}
+
+	if (alm->enabled)
+		ret = tps65910_rtc_alarm_irq_enable(dev, 1);
+
+	return ret;
+}
+
+static int tps65910_rtc_set_calibration(struct device *dev, int calibration)
+{
+	unsigned char comp_data[NUM_COMP_REGS];
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	s16 value;
+	int ret;
+
+	/*
+	 * TPS65910 uses two's complement 16 bit value for compensation for RTC
+	 * crystal inaccuracies. One time every hour when seconds counter
+	 * increments from 0 to 1 compensation value will be added to internal
+	 * RTC counter value.
+	 *
+	 * Compensation value 0x7FFF is prohibited value.
+	 *
+	 * Valid range for compensation value: [-32768 .. 32766]
+	 */
+	if ((calibration < -32768) || (calibration > 32766)) {
+		dev_err(dev, "RTC calibration value out of range: %d\n",
+			calibration);
+		return -EINVAL;
+	}
+
+	value = (s16)calibration;
+
+	comp_data[0] = (u16)value & 0xFF;
+	comp_data[1] = ((u16)value >> 8) & 0xFF;
+
+	/* Update all the compensation registers in one shot */
+	ret = regmap_bulk_write(tps->regmap, TPS65910_RTC_COMP_LSB,
+		comp_data, NUM_COMP_REGS);
+	if (ret < 0) {
+		dev_err(dev, "rtc_set_calibration error: %d\n", ret);
+		return ret;
+	}
+
+	/* Enable automatic compensation */
+	ret = regmap_update_bits(tps->regmap, TPS65910_RTC_CTRL,
+		TPS65910_RTC_CTRL_AUTO_COMP, TPS65910_RTC_CTRL_AUTO_COMP);
+	if (ret < 0)
+		dev_err(dev, "auto_comp enable failed with error: %d\n", ret);
+
+	return ret;
+}
+
+static int tps65910_rtc_get_calibration(struct device *dev, int *calibration)
+{
+	unsigned char comp_data[NUM_COMP_REGS];
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	unsigned int ctrl;
+	u16 value;
+	int ret;
+
+	ret = regmap_read(tps->regmap, TPS65910_RTC_CTRL, &ctrl);
+	if (ret < 0)
+		return ret;
+
+	/* If automatic compensation is not enabled report back zero */
+	if (!(ctrl & TPS65910_RTC_CTRL_AUTO_COMP)) {
+		*calibration = 0;
+		return 0;
+	}
+
+	ret = regmap_bulk_read(tps->regmap, TPS65910_RTC_COMP_LSB, comp_data,
+		NUM_COMP_REGS);
+	if (ret < 0) {
+		dev_err(dev, "rtc_get_calibration error: %d\n", ret);
+		return ret;
+	}
+
+	value = (u16)comp_data[0] | ((u16)comp_data[1] << 8);
+
+	*calibration = (s16)value;
+
+	return 0;
+}
+
+static int tps65910_read_offset(struct device *dev, long *offset)
+{
+	int calibration;
+	s64 tmp;
+	int ret;
+
+	ret = tps65910_rtc_get_calibration(dev, &calibration);
+	if (ret < 0)
+		return ret;
+
+	/* Convert from RTC calibration register format to ppb format */
+	tmp = calibration * (s64)PPB_MULT;
+	if (tmp < 0)
+		tmp -= TICKS_PER_HOUR / 2LL;
+	else
+		tmp += TICKS_PER_HOUR / 2LL;
+	tmp = div_s64(tmp, TICKS_PER_HOUR);
+
+	/* Offset value operates in negative way, so swap sign */
+	*offset = (long)-tmp;
+
+	return 0;
+}
+
+static int tps65910_set_offset(struct device *dev, long offset)
+{
+	int calibration;
+	s64 tmp;
+	int ret;
+
+	/* Make sure offset value is within supported range */
+	if (offset < MIN_OFFSET || offset > MAX_OFFSET)
+		return -ERANGE;
+
+	/* Convert from ppb format to RTC calibration register format */
+	tmp = offset * (s64)TICKS_PER_HOUR;
+	if (tmp < 0)
+		tmp -= PPB_MULT / 2LL;
+	else
+		tmp += PPB_MULT / 2LL;
+	tmp = div_s64(tmp, PPB_MULT);
+
+	/* Offset value operates in negative way, so swap sign */
+	calibration = (int)-tmp;
+
+	ret = tps65910_rtc_set_calibration(dev, calibration);
+
+	return ret;
+}
+
+static irqreturn_t tps65910_rtc_interrupt(int irq, void *rtc)
+{
+	struct device *dev = rtc;
+	unsigned long events = 0;
+	struct tps65910 *tps = dev_get_drvdata(dev->parent);
+	struct tps65910_rtc *tps_rtc = dev_get_drvdata(dev);
+	int ret;
+	u32 rtc_reg;
+
+	ret = regmap_read(tps->regmap, TPS65910_RTC_STATUS, &rtc_reg);
+	if (ret)
+		return IRQ_NONE;
+
+	if (rtc_reg & TPS65910_RTC_STATUS_ALARM)
+		events = RTC_IRQF | RTC_AF;
+
+	ret = regmap_write(tps->regmap, TPS65910_RTC_STATUS, rtc_reg);
+	if (ret)
+		return IRQ_NONE;
+
+	/* Notify RTC core on event */
+	rtc_update_irq(tps_rtc->rtc, 1, events);
+
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops tps65910_rtc_ops = {
+	.read_time	= tps65910_rtc_read_time,
+	.set_time	= tps65910_rtc_set_time,
+	.read_alarm	= tps65910_rtc_read_alarm,
+	.set_alarm	= tps65910_rtc_set_alarm,
+	.alarm_irq_enable = tps65910_rtc_alarm_irq_enable,
+	.read_offset	= tps65910_read_offset,
+	.set_offset	= tps65910_set_offset,
+};
+
+static int tps65910_rtc_probe(struct platform_device *pdev)
+{
+	struct tps65910 *tps65910 = NULL;
+	struct tps65910_rtc *tps_rtc = NULL;
+	int ret;
+	int irq;
+	u32 rtc_reg;
+
+	tps65910 = dev_get_drvdata(pdev->dev.parent);
+
+	tps_rtc = devm_kzalloc(&pdev->dev, sizeof(struct tps65910_rtc),
+			GFP_KERNEL);
+	if (!tps_rtc)
+		return -ENOMEM;
+
+	tps_rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(tps_rtc->rtc))
+		return PTR_ERR(tps_rtc->rtc);
+
+	/* Clear pending interrupts */
+	ret = regmap_read(tps65910->regmap, TPS65910_RTC_STATUS, &rtc_reg);
+	if (ret < 0)
+		return ret;
+
+	ret = regmap_write(tps65910->regmap, TPS65910_RTC_STATUS, rtc_reg);
+	if (ret < 0)
+		return ret;
+
+	dev_dbg(&pdev->dev, "Enabling rtc-tps65910.\n");
+
+	/* Enable RTC digital power domain */
+	ret = regmap_update_bits(tps65910->regmap, TPS65910_DEVCTRL,
+		DEVCTRL_RTC_PWDN_MASK, 0 << DEVCTRL_RTC_PWDN_SHIFT);
+	if (ret < 0)
+		return ret;
+
+	rtc_reg = TPS65910_RTC_CTRL_STOP_RTC;
+	ret = regmap_write(tps65910->regmap, TPS65910_RTC_CTRL, rtc_reg);
+	if (ret < 0)
+		return ret;
+
+	platform_set_drvdata(pdev, tps_rtc);
+
+	irq  = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	ret = devm_request_threaded_irq(&pdev->dev, irq, NULL,
+		tps65910_rtc_interrupt, IRQF_TRIGGER_LOW,
+		dev_name(&pdev->dev), &pdev->dev);
+	if (ret < 0)
+		irq = -1;
+
+	tps_rtc->irq = irq;
+	if (irq != -1) {
+		if (device_property_present(tps65910->dev, "wakeup-source"))
+			device_init_wakeup(&pdev->dev, true);
+		else
+			device_set_wakeup_capable(&pdev->dev, 1);
+	} else {
+		clear_bit(RTC_FEATURE_ALARM, tps_rtc->rtc->features);
+	}
+
+	tps_rtc->rtc->ops = &tps65910_rtc_ops;
+	tps_rtc->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	tps_rtc->rtc->range_max = RTC_TIMESTAMP_END_2099;
+
+	return devm_rtc_register_device(tps_rtc->rtc);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int tps65910_rtc_suspend(struct device *dev)
+{
+	struct tps65910_rtc *tps_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(tps_rtc->irq);
+	return 0;
+}
+
+static int tps65910_rtc_resume(struct device *dev)
+{
+	struct tps65910_rtc *tps_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(tps_rtc->irq);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(tps65910_rtc_pm_ops, tps65910_rtc_suspend,
+			tps65910_rtc_resume);
+
+static struct platform_driver tps65910_rtc_driver = {
+	.probe		= tps65910_rtc_probe,
+	.driver		= {
+		.name	= "tps65910-rtc",
+		.pm	= &tps65910_rtc_pm_ops,
+	},
+};
+
+module_platform_driver(tps65910_rtc_driver);
+MODULE_ALIAS("platform:tps65910-rtc");
+MODULE_AUTHOR("Venu Byravarasu <vbyravarasu@nvidia.com>");
+MODULE_DESCRIPTION("TI TPS65910 RTC driver");
+MODULE_LICENSE("GPL");