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, 362 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-palmas.c b/drivers/rtc/rtc-palmas.c
new file mode 100644
index 000000000..aecada6bc
--- /dev/null
+++ b/drivers/rtc/rtc-palmas.c
@@ -0,0 +1,362 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * rtc-palmas.c -- Palmas Real Time Clock driver.
+
+ * RTC driver for TI Palma series devices like TPS65913,
+ * TPS65914 power management IC.
+ *
+ * Copyright (c) 2012, NVIDIA Corporation.
+ *
+ * Author: Laxman Dewangan <ldewangan@nvidia.com>
+ */
+
+#include <linux/bcd.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/mfd/palmas.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/rtc.h>
+#include <linux/types.h>
+#include <linux/platform_device.h>
+#include <linux/pm.h>
+
+struct palmas_rtc {
+	struct rtc_device	*rtc;
+	struct device		*dev;
+	unsigned int		irq;
+};
+
+/* Total number of RTC registers needed to set time*/
+#define PALMAS_NUM_TIME_REGS	(PALMAS_YEARS_REG - PALMAS_SECONDS_REG + 1)
+
+static int palmas_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	unsigned char rtc_data[PALMAS_NUM_TIME_REGS];
+	struct palmas *palmas = dev_get_drvdata(dev->parent);
+	int ret;
+
+	/* Copy RTC counting registers to static registers or latches */
+	ret = palmas_update_bits(palmas, PALMAS_RTC_BASE, PALMAS_RTC_CTRL_REG,
+		PALMAS_RTC_CTRL_REG_GET_TIME, PALMAS_RTC_CTRL_REG_GET_TIME);
+	if (ret < 0) {
+		dev_err(dev, "RTC CTRL reg update failed, err: %d\n", ret);
+		return ret;
+	}
+
+	ret = palmas_bulk_read(palmas, PALMAS_RTC_BASE, PALMAS_SECONDS_REG,
+			rtc_data, PALMAS_NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "RTC_SECONDS reg read failed, 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 palmas_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	unsigned char rtc_data[PALMAS_NUM_TIME_REGS];
+	struct palmas *palmas = 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 = palmas_update_bits(palmas, PALMAS_RTC_BASE, PALMAS_RTC_CTRL_REG,
+		PALMAS_RTC_CTRL_REG_STOP_RTC, 0);
+	if (ret < 0) {
+		dev_err(dev, "RTC stop failed, err = %d\n", ret);
+		return ret;
+	}
+
+	ret = palmas_bulk_write(palmas, PALMAS_RTC_BASE, PALMAS_SECONDS_REG,
+		rtc_data, PALMAS_NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "RTC_SECONDS reg write failed, err = %d\n", ret);
+		return ret;
+	}
+
+	/* Start back RTC */
+	ret = palmas_update_bits(palmas, PALMAS_RTC_BASE, PALMAS_RTC_CTRL_REG,
+		PALMAS_RTC_CTRL_REG_STOP_RTC, PALMAS_RTC_CTRL_REG_STOP_RTC);
+	if (ret < 0)
+		dev_err(dev, "RTC start failed, err = %d\n", ret);
+	return ret;
+}
+
+static int palmas_rtc_alarm_irq_enable(struct device *dev, unsigned enabled)
+{
+	struct palmas *palmas = dev_get_drvdata(dev->parent);
+	u8 val;
+
+	val = enabled ? PALMAS_RTC_INTERRUPTS_REG_IT_ALARM : 0;
+	return palmas_write(palmas, PALMAS_RTC_BASE,
+		PALMAS_RTC_INTERRUPTS_REG, val);
+}
+
+static int palmas_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	unsigned char alarm_data[PALMAS_NUM_TIME_REGS];
+	u32 int_val;
+	struct palmas *palmas = dev_get_drvdata(dev->parent);
+	int ret;
+
+	ret = palmas_bulk_read(palmas, PALMAS_RTC_BASE,
+			PALMAS_ALARM_SECONDS_REG,
+			alarm_data, PALMAS_NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "RTC_ALARM_SECONDS read failed, err = %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 = palmas_read(palmas, PALMAS_RTC_BASE, PALMAS_RTC_INTERRUPTS_REG,
+			&int_val);
+	if (ret < 0) {
+		dev_err(dev, "RTC_INTERRUPTS reg read failed, err = %d\n", ret);
+		return ret;
+	}
+
+	if (int_val & PALMAS_RTC_INTERRUPTS_REG_IT_ALARM)
+		alm->enabled = 1;
+	return ret;
+}
+
+static int palmas_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	unsigned char alarm_data[PALMAS_NUM_TIME_REGS];
+	struct palmas *palmas = dev_get_drvdata(dev->parent);
+	int ret;
+
+	ret = palmas_rtc_alarm_irq_enable(dev, 0);
+	if (ret < 0) {
+		dev_err(dev, "Disable RTC alarm failed\n");
+		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);
+
+	ret = palmas_bulk_write(palmas, PALMAS_RTC_BASE,
+		PALMAS_ALARM_SECONDS_REG, alarm_data, PALMAS_NUM_TIME_REGS);
+	if (ret < 0) {
+		dev_err(dev, "ALARM_SECONDS_REG write failed, err = %d\n", ret);
+		return ret;
+	}
+
+	if (alm->enabled)
+		ret = palmas_rtc_alarm_irq_enable(dev, 1);
+	return ret;
+}
+
+static int palmas_clear_interrupts(struct device *dev)
+{
+	struct palmas *palmas = dev_get_drvdata(dev->parent);
+	unsigned int rtc_reg;
+	int ret;
+
+	ret = palmas_read(palmas, PALMAS_RTC_BASE, PALMAS_RTC_STATUS_REG,
+				&rtc_reg);
+	if (ret < 0) {
+		dev_err(dev, "RTC_STATUS read failed, err = %d\n", ret);
+		return ret;
+	}
+
+	ret = palmas_write(palmas, PALMAS_RTC_BASE, PALMAS_RTC_STATUS_REG,
+			rtc_reg);
+	if (ret < 0) {
+		dev_err(dev, "RTC_STATUS write failed, err = %d\n", ret);
+		return ret;
+	}
+	return 0;
+}
+
+static irqreturn_t palmas_rtc_interrupt(int irq, void *context)
+{
+	struct palmas_rtc *palmas_rtc = context;
+	struct device *dev = palmas_rtc->dev;
+	int ret;
+
+	ret = palmas_clear_interrupts(dev);
+	if (ret < 0) {
+		dev_err(dev, "RTC interrupt clear failed, err = %d\n", ret);
+		return IRQ_NONE;
+	}
+
+	rtc_update_irq(palmas_rtc->rtc, 1, RTC_IRQF | RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops palmas_rtc_ops = {
+	.read_time	= palmas_rtc_read_time,
+	.set_time	= palmas_rtc_set_time,
+	.read_alarm	= palmas_rtc_read_alarm,
+	.set_alarm	= palmas_rtc_set_alarm,
+	.alarm_irq_enable = palmas_rtc_alarm_irq_enable,
+};
+
+static int palmas_rtc_probe(struct platform_device *pdev)
+{
+	struct palmas *palmas = dev_get_drvdata(pdev->dev.parent);
+	struct palmas_rtc *palmas_rtc = NULL;
+	int ret;
+	bool enable_bb_charging = false;
+	bool high_bb_charging = false;
+
+	if (pdev->dev.of_node) {
+		enable_bb_charging = of_property_read_bool(pdev->dev.of_node,
+					"ti,backup-battery-chargeable");
+		high_bb_charging = of_property_read_bool(pdev->dev.of_node,
+					"ti,backup-battery-charge-high-current");
+	}
+
+	palmas_rtc = devm_kzalloc(&pdev->dev, sizeof(struct palmas_rtc),
+			GFP_KERNEL);
+	if (!palmas_rtc)
+		return -ENOMEM;
+
+	/* Clear pending interrupts */
+	ret = palmas_clear_interrupts(&pdev->dev);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "clear RTC int failed, err = %d\n", ret);
+		return ret;
+	}
+
+	palmas_rtc->dev = &pdev->dev;
+	platform_set_drvdata(pdev, palmas_rtc);
+
+	if (enable_bb_charging) {
+		unsigned reg = PALMAS_BACKUP_BATTERY_CTRL_BBS_BBC_LOW_ICHRG;
+
+		if (high_bb_charging)
+			reg = 0;
+
+		ret = palmas_update_bits(palmas, PALMAS_PMU_CONTROL_BASE,
+			PALMAS_BACKUP_BATTERY_CTRL,
+			PALMAS_BACKUP_BATTERY_CTRL_BBS_BBC_LOW_ICHRG, reg);
+		if (ret < 0) {
+			dev_err(&pdev->dev,
+				"BACKUP_BATTERY_CTRL update failed, %d\n", ret);
+			return ret;
+		}
+
+		ret = palmas_update_bits(palmas, PALMAS_PMU_CONTROL_BASE,
+			PALMAS_BACKUP_BATTERY_CTRL,
+			PALMAS_BACKUP_BATTERY_CTRL_BB_CHG_EN,
+			PALMAS_BACKUP_BATTERY_CTRL_BB_CHG_EN);
+		if (ret < 0) {
+			dev_err(&pdev->dev,
+				"BACKUP_BATTERY_CTRL update failed, %d\n", ret);
+			return ret;
+		}
+	}
+
+	/* Start RTC */
+	ret = palmas_update_bits(palmas, PALMAS_RTC_BASE, PALMAS_RTC_CTRL_REG,
+			PALMAS_RTC_CTRL_REG_STOP_RTC,
+			PALMAS_RTC_CTRL_REG_STOP_RTC);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "RTC_CTRL write failed, err = %d\n", ret);
+		return ret;
+	}
+
+	palmas_rtc->irq = platform_get_irq(pdev, 0);
+
+	device_init_wakeup(&pdev->dev, true);
+	palmas_rtc->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
+				&palmas_rtc_ops, THIS_MODULE);
+	if (IS_ERR(palmas_rtc->rtc)) {
+		ret = PTR_ERR(palmas_rtc->rtc);
+		dev_err(&pdev->dev, "RTC register failed, err = %d\n", ret);
+		return ret;
+	}
+
+	ret = devm_request_threaded_irq(&pdev->dev, palmas_rtc->irq, NULL,
+			palmas_rtc_interrupt,
+			IRQF_TRIGGER_LOW | IRQF_ONESHOT,
+			dev_name(&pdev->dev), palmas_rtc);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "IRQ request failed, err = %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void palmas_rtc_remove(struct platform_device *pdev)
+{
+	palmas_rtc_alarm_irq_enable(&pdev->dev, 0);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int palmas_rtc_suspend(struct device *dev)
+{
+	struct palmas_rtc *palmas_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(palmas_rtc->irq);
+	return 0;
+}
+
+static int palmas_rtc_resume(struct device *dev)
+{
+	struct palmas_rtc *palmas_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(palmas_rtc->irq);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(palmas_rtc_pm_ops, palmas_rtc_suspend,
+			 palmas_rtc_resume);
+
+#ifdef CONFIG_OF
+static const struct of_device_id of_palmas_rtc_match[] = {
+	{ .compatible = "ti,palmas-rtc"},
+	{ },
+};
+MODULE_DEVICE_TABLE(of, of_palmas_rtc_match);
+#endif
+
+static struct platform_driver palmas_rtc_driver = {
+	.probe		= palmas_rtc_probe,
+	.remove		= palmas_rtc_remove,
+	.driver		= {
+		.name	= "palmas-rtc",
+		.pm	= &palmas_rtc_pm_ops,
+		.of_match_table = of_match_ptr(of_palmas_rtc_match),
+	},
+};
+
+module_platform_driver(palmas_rtc_driver);
+
+MODULE_ALIAS("platform:palmas_rtc");
+MODULE_DESCRIPTION("TI PALMAS series RTC driver");
+MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
+MODULE_LICENSE("GPL v2");