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, 381 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-88pm860x.c b/drivers/rtc/rtc-88pm860x.c
new file mode 100644
index 000000000..964cd048f
--- /dev/null
+++ b/drivers/rtc/rtc-88pm860x.c
@@ -0,0 +1,381 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Real Time Clock driver for Marvell 88PM860x PMIC
+ *
+ * Copyright (c) 2010 Marvell International Ltd.
+ * Author:	Haojian Zhuang <haojian.zhuang@marvell.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/mutex.h>
+#include <linux/rtc.h>
+#include <linux/delay.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/88pm860x.h>
+
+#define VRTC_CALIBRATION
+
+struct pm860x_rtc_info {
+	struct pm860x_chip	*chip;
+	struct i2c_client	*i2c;
+	struct rtc_device	*rtc_dev;
+	struct device		*dev;
+	struct delayed_work	calib_work;
+
+	int			irq;
+	int			vrtc;
+};
+
+#define REG_VRTC_MEAS1		0x7D
+
+#define REG0_ADDR		0xB0
+#define REG1_ADDR		0xB2
+#define REG2_ADDR		0xB4
+#define REG3_ADDR		0xB6
+
+#define REG0_DATA		0xB1
+#define REG1_DATA		0xB3
+#define REG2_DATA		0xB5
+#define REG3_DATA		0xB7
+
+/* bit definitions of Measurement Enable Register 2 (0x51) */
+#define MEAS2_VRTC		(1 << 0)
+
+/* bit definitions of RTC Register 1 (0xA0) */
+#define ALARM_EN		(1 << 3)
+#define ALARM_WAKEUP		(1 << 4)
+#define ALARM			(1 << 5)
+#define RTC1_USE_XO		(1 << 7)
+
+#define VRTC_CALIB_INTERVAL	(HZ * 60 * 10)		/* 10 minutes */
+
+static irqreturn_t rtc_update_handler(int irq, void *data)
+{
+	struct pm860x_rtc_info *info = (struct pm860x_rtc_info *)data;
+	int mask;
+
+	mask = ALARM | ALARM_WAKEUP;
+	pm860x_set_bits(info->i2c, PM8607_RTC1, mask | ALARM_EN, mask);
+	rtc_update_irq(info->rtc_dev, 1, RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static int pm860x_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct pm860x_rtc_info *info = dev_get_drvdata(dev);
+
+	if (enabled)
+		pm860x_set_bits(info->i2c, PM8607_RTC1, ALARM_EN, ALARM_EN);
+	else
+		pm860x_set_bits(info->i2c, PM8607_RTC1, ALARM_EN, 0);
+	return 0;
+}
+
+static int pm860x_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct pm860x_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[8];
+	unsigned long ticks, base, data;
+
+	pm860x_page_bulk_read(info->i2c, REG0_ADDR, 8, buf);
+	dev_dbg(info->dev, "%x-%x-%x-%x-%x-%x-%x-%x\n", buf[0], buf[1],
+		buf[2], buf[3], buf[4], buf[5], buf[6], buf[7]);
+	base = ((unsigned long)buf[1] << 24) | (buf[3] << 16) |
+		(buf[5] << 8) | buf[7];
+
+	/* load 32-bit read-only counter */
+	pm860x_bulk_read(info->i2c, PM8607_RTC_COUNTER1, 4, buf);
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	ticks = base + data;
+	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
+		base, data, ticks);
+
+	rtc_time64_to_tm(ticks, tm);
+
+	return 0;
+}
+
+static int pm860x_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct pm860x_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[4];
+	unsigned long ticks, base, data;
+
+	ticks = rtc_tm_to_time64(tm);
+
+	/* load 32-bit read-only counter */
+	pm860x_bulk_read(info->i2c, PM8607_RTC_COUNTER1, 4, buf);
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	base = ticks - data;
+	dev_dbg(info->dev, "set base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
+		base, data, ticks);
+
+	pm860x_page_reg_write(info->i2c, REG0_DATA, (base >> 24) & 0xFF);
+	pm860x_page_reg_write(info->i2c, REG1_DATA, (base >> 16) & 0xFF);
+	pm860x_page_reg_write(info->i2c, REG2_DATA, (base >> 8) & 0xFF);
+	pm860x_page_reg_write(info->i2c, REG3_DATA, base & 0xFF);
+
+	return 0;
+}
+
+static int pm860x_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct pm860x_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[8];
+	unsigned long ticks, base, data;
+	int ret;
+
+	pm860x_page_bulk_read(info->i2c, REG0_ADDR, 8, buf);
+	dev_dbg(info->dev, "%x-%x-%x-%x-%x-%x-%x-%x\n", buf[0], buf[1],
+		buf[2], buf[3], buf[4], buf[5], buf[6], buf[7]);
+	base = ((unsigned long)buf[1] << 24) | (buf[3] << 16) |
+		(buf[5] << 8) | buf[7];
+
+	pm860x_bulk_read(info->i2c, PM8607_RTC_EXPIRE1, 4, buf);
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	ticks = base + data;
+	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
+		base, data, ticks);
+
+	rtc_time64_to_tm(ticks, &alrm->time);
+	ret = pm860x_reg_read(info->i2c, PM8607_RTC1);
+	alrm->enabled = (ret & ALARM_EN) ? 1 : 0;
+	alrm->pending = (ret & (ALARM | ALARM_WAKEUP)) ? 1 : 0;
+	return 0;
+}
+
+static int pm860x_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct pm860x_rtc_info *info = dev_get_drvdata(dev);
+	unsigned long ticks, base, data;
+	unsigned char buf[8];
+	int mask;
+
+	pm860x_set_bits(info->i2c, PM8607_RTC1, ALARM_EN, 0);
+
+	pm860x_page_bulk_read(info->i2c, REG0_ADDR, 8, buf);
+	dev_dbg(info->dev, "%x-%x-%x-%x-%x-%x-%x-%x\n", buf[0], buf[1],
+		buf[2], buf[3], buf[4], buf[5], buf[6], buf[7]);
+	base = ((unsigned long)buf[1] << 24) | (buf[3] << 16) |
+		(buf[5] << 8) | buf[7];
+
+	ticks = rtc_tm_to_time64(&alrm->time);
+	data = ticks - base;
+
+	buf[0] = data & 0xff;
+	buf[1] = (data >> 8) & 0xff;
+	buf[2] = (data >> 16) & 0xff;
+	buf[3] = (data >> 24) & 0xff;
+	pm860x_bulk_write(info->i2c, PM8607_RTC_EXPIRE1, 4, buf);
+	if (alrm->enabled) {
+		mask = ALARM | ALARM_WAKEUP | ALARM_EN;
+		pm860x_set_bits(info->i2c, PM8607_RTC1, mask, mask);
+	} else {
+		mask = ALARM | ALARM_WAKEUP | ALARM_EN;
+		pm860x_set_bits(info->i2c, PM8607_RTC1, mask,
+				ALARM | ALARM_WAKEUP);
+	}
+	return 0;
+}
+
+static const struct rtc_class_ops pm860x_rtc_ops = {
+	.read_time	= pm860x_rtc_read_time,
+	.set_time	= pm860x_rtc_set_time,
+	.read_alarm	= pm860x_rtc_read_alarm,
+	.set_alarm	= pm860x_rtc_set_alarm,
+	.alarm_irq_enable = pm860x_rtc_alarm_irq_enable,
+};
+
+#ifdef VRTC_CALIBRATION
+static void calibrate_vrtc_work(struct work_struct *work)
+{
+	struct pm860x_rtc_info *info = container_of(work,
+		struct pm860x_rtc_info, calib_work.work);
+	unsigned char buf[2];
+	unsigned int sum, data, mean, vrtc_set;
+	int i;
+
+	for (i = 0, sum = 0; i < 16; i++) {
+		msleep(100);
+		pm860x_bulk_read(info->i2c, REG_VRTC_MEAS1, 2, buf);
+		data = (buf[0] << 4) | buf[1];
+		data = (data * 5400) >> 12;	/* convert to mv */
+		sum += data;
+	}
+	mean = sum >> 4;
+	vrtc_set = 2700 + (info->vrtc & 0x3) * 200;
+	dev_dbg(info->dev, "mean:%d, vrtc_set:%d\n", mean, vrtc_set);
+
+	sum = pm860x_reg_read(info->i2c, PM8607_RTC_MISC1);
+	data = sum & 0x3;
+	if ((mean + 200) < vrtc_set) {
+		/* try higher voltage */
+		if (++data == 4)
+			goto out;
+		data = (sum & 0xf8) | (data & 0x3);
+		pm860x_reg_write(info->i2c, PM8607_RTC_MISC1, data);
+	} else if ((mean - 200) > vrtc_set) {
+		/* try lower voltage */
+		if (data-- == 0)
+			goto out;
+		data = (sum & 0xf8) | (data & 0x3);
+		pm860x_reg_write(info->i2c, PM8607_RTC_MISC1, data);
+	} else
+		goto out;
+	dev_dbg(info->dev, "set 0x%x to RTC_MISC1\n", data);
+	/* trigger next calibration since VRTC is updated */
+	schedule_delayed_work(&info->calib_work, VRTC_CALIB_INTERVAL);
+	return;
+out:
+	/* disable measurement */
+	pm860x_set_bits(info->i2c, PM8607_MEAS_EN2, MEAS2_VRTC, 0);
+	dev_dbg(info->dev, "finish VRTC calibration\n");
+	return;
+}
+#endif
+
+#ifdef CONFIG_OF
+static int pm860x_rtc_dt_init(struct platform_device *pdev,
+			      struct pm860x_rtc_info *info)
+{
+	struct device_node *np = pdev->dev.parent->of_node;
+	int ret;
+	if (!np)
+		return -ENODEV;
+	np = of_get_child_by_name(np, "rtc");
+	if (!np) {
+		dev_err(&pdev->dev, "failed to find rtc node\n");
+		return -ENODEV;
+	}
+	ret = of_property_read_u32(np, "marvell,88pm860x-vrtc", &info->vrtc);
+	if (ret)
+		info->vrtc = 0;
+	of_node_put(np);
+	return 0;
+}
+#else
+#define pm860x_rtc_dt_init(x, y)	do { } while (0)
+#endif
+
+static int pm860x_rtc_probe(struct platform_device *pdev)
+{
+	struct pm860x_chip *chip = dev_get_drvdata(pdev->dev.parent);
+	struct pm860x_rtc_info *info;
+	int ret;
+
+	info = devm_kzalloc(&pdev->dev, sizeof(struct pm860x_rtc_info),
+			    GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+	info->irq = platform_get_irq(pdev, 0);
+	if (info->irq < 0)
+		return info->irq;
+
+	info->chip = chip;
+	info->i2c = (chip->id == CHIP_PM8607) ? chip->client : chip->companion;
+	info->dev = &pdev->dev;
+	dev_set_drvdata(&pdev->dev, info);
+
+	info->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(info->rtc_dev))
+		return PTR_ERR(info->rtc_dev);
+
+	ret = devm_request_threaded_irq(&pdev->dev, info->irq, NULL,
+					rtc_update_handler, IRQF_ONESHOT, "rtc",
+					info);
+	if (ret < 0) {
+		dev_err(chip->dev, "Failed to request IRQ: #%d: %d\n",
+			info->irq, ret);
+		return ret;
+	}
+
+	/* set addresses of 32-bit base value for RTC time */
+	pm860x_page_reg_write(info->i2c, REG0_ADDR, REG0_DATA);
+	pm860x_page_reg_write(info->i2c, REG1_ADDR, REG1_DATA);
+	pm860x_page_reg_write(info->i2c, REG2_ADDR, REG2_DATA);
+	pm860x_page_reg_write(info->i2c, REG3_ADDR, REG3_DATA);
+
+	pm860x_rtc_dt_init(pdev, info);
+
+	info->rtc_dev->ops = &pm860x_rtc_ops;
+	info->rtc_dev->range_max = U32_MAX;
+
+	ret = devm_rtc_register_device(info->rtc_dev);
+	if (ret)
+		return ret;
+
+	/*
+	 * enable internal XO instead of internal 3.25MHz clock since it can
+	 * free running in PMIC power-down state.
+	 */
+	pm860x_set_bits(info->i2c, PM8607_RTC1, RTC1_USE_XO, RTC1_USE_XO);
+
+#ifdef VRTC_CALIBRATION
+	/* <00> -- 2.7V, <01> -- 2.9V, <10> -- 3.1V, <11> -- 3.3V */
+	pm860x_set_bits(info->i2c, PM8607_MEAS_EN2, MEAS2_VRTC, MEAS2_VRTC);
+
+	/* calibrate VRTC */
+	INIT_DELAYED_WORK(&info->calib_work, calibrate_vrtc_work);
+	schedule_delayed_work(&info->calib_work, VRTC_CALIB_INTERVAL);
+#endif	/* VRTC_CALIBRATION */
+
+	device_init_wakeup(&pdev->dev, true);
+
+	return 0;
+}
+
+static void pm860x_rtc_remove(struct platform_device *pdev)
+{
+	struct pm860x_rtc_info *info = platform_get_drvdata(pdev);
+
+#ifdef VRTC_CALIBRATION
+	cancel_delayed_work_sync(&info->calib_work);
+	/* disable measurement */
+	pm860x_set_bits(info->i2c, PM8607_MEAS_EN2, MEAS2_VRTC, 0);
+#endif	/* VRTC_CALIBRATION */
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int pm860x_rtc_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct pm860x_chip *chip = dev_get_drvdata(pdev->dev.parent);
+
+	if (device_may_wakeup(dev))
+		chip->wakeup_flag |= 1 << PM8607_IRQ_RTC;
+	return 0;
+}
+static int pm860x_rtc_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct pm860x_chip *chip = dev_get_drvdata(pdev->dev.parent);
+
+	if (device_may_wakeup(dev))
+		chip->wakeup_flag &= ~(1 << PM8607_IRQ_RTC);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(pm860x_rtc_pm_ops, pm860x_rtc_suspend, pm860x_rtc_resume);
+
+static struct platform_driver pm860x_rtc_driver = {
+	.driver		= {
+		.name	= "88pm860x-rtc",
+		.pm	= &pm860x_rtc_pm_ops,
+	},
+	.probe		= pm860x_rtc_probe,
+	.remove		= pm860x_rtc_remove,
+};
+
+module_platform_driver(pm860x_rtc_driver);
+
+MODULE_DESCRIPTION("Marvell 88PM860x RTC driver");
+MODULE_AUTHOR("Haojian Zhuang <haojian.zhuang@marvell.com>");
+MODULE_LICENSE("GPL");