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, 399 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-da9055.c b/drivers/rtc/rtc-da9055.c
new file mode 100644
index 000000000..05adec6b7
--- /dev/null
+++ b/drivers/rtc/rtc-da9055.c
@@ -0,0 +1,399 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Real time clock driver for DA9055
+ *
+ * Copyright(c) 2012 Dialog Semiconductor Ltd.
+ *
+ * Author: Dajun Dajun Chen <dajun.chen@diasemi.com>
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#include <linux/mfd/da9055/core.h>
+#include <linux/mfd/da9055/reg.h>
+#include <linux/mfd/da9055/pdata.h>
+
+struct da9055_rtc {
+	struct rtc_device *rtc;
+	struct da9055 *da9055;
+	int alarm_enable;
+};
+
+static int da9055_rtc_enable_alarm(struct da9055_rtc *rtc, bool enable)
+{
+	int ret;
+	if (enable) {
+		ret = da9055_reg_update(rtc->da9055, DA9055_REG_ALARM_Y,
+					DA9055_RTC_ALM_EN,
+					DA9055_RTC_ALM_EN);
+		if (ret != 0)
+			dev_err(rtc->da9055->dev, "Failed to enable ALM: %d\n",
+				ret);
+		rtc->alarm_enable = 1;
+	} else {
+		ret = da9055_reg_update(rtc->da9055, DA9055_REG_ALARM_Y,
+					DA9055_RTC_ALM_EN, 0);
+		if (ret != 0)
+			dev_err(rtc->da9055->dev,
+				"Failed to disable ALM: %d\n", ret);
+		rtc->alarm_enable = 0;
+	}
+	return ret;
+}
+
+static irqreturn_t da9055_rtc_alm_irq(int irq, void *data)
+{
+	struct da9055_rtc *rtc = data;
+
+	da9055_rtc_enable_alarm(rtc, 0);
+	rtc_update_irq(rtc->rtc, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static int da9055_read_alarm(struct da9055 *da9055, struct rtc_time *rtc_tm)
+{
+	int ret;
+	uint8_t v[5];
+
+	ret = da9055_group_read(da9055, DA9055_REG_ALARM_MI, 5, v);
+	if (ret != 0) {
+		dev_err(da9055->dev, "Failed to group read ALM: %d\n", ret);
+		return ret;
+	}
+
+	rtc_tm->tm_year = (v[4] & DA9055_RTC_ALM_YEAR) + 100;
+	rtc_tm->tm_mon  = (v[3] & DA9055_RTC_ALM_MONTH) - 1;
+	rtc_tm->tm_mday = v[2] & DA9055_RTC_ALM_DAY;
+	rtc_tm->tm_hour = v[1] & DA9055_RTC_ALM_HOUR;
+	rtc_tm->tm_min  = v[0] & DA9055_RTC_ALM_MIN;
+	rtc_tm->tm_sec = 0;
+
+	return rtc_valid_tm(rtc_tm);
+}
+
+static int da9055_set_alarm(struct da9055 *da9055, struct rtc_time *rtc_tm)
+{
+	int ret;
+	uint8_t v[2];
+
+	rtc_tm->tm_year -= 100;
+	rtc_tm->tm_mon += 1;
+
+	ret = da9055_reg_update(da9055, DA9055_REG_ALARM_MI,
+				DA9055_RTC_ALM_MIN, rtc_tm->tm_min);
+	if (ret != 0) {
+		dev_err(da9055->dev, "Failed to write ALRM MIN: %d\n", ret);
+		return ret;
+	}
+
+	v[0] = rtc_tm->tm_hour;
+	v[1] = rtc_tm->tm_mday;
+
+	ret = da9055_group_write(da9055, DA9055_REG_ALARM_H, 2, v);
+	if (ret < 0)
+		return ret;
+
+	ret = da9055_reg_update(da9055, DA9055_REG_ALARM_MO,
+				DA9055_RTC_ALM_MONTH, rtc_tm->tm_mon);
+	if (ret < 0)
+		dev_err(da9055->dev, "Failed to write ALM Month:%d\n", ret);
+
+	ret = da9055_reg_update(da9055, DA9055_REG_ALARM_Y,
+				DA9055_RTC_ALM_YEAR, rtc_tm->tm_year);
+	if (ret < 0)
+		dev_err(da9055->dev, "Failed to write ALM Year:%d\n", ret);
+
+	return ret;
+}
+
+static int da9055_rtc_get_alarm_status(struct da9055 *da9055)
+{
+	int ret;
+
+	ret = da9055_reg_read(da9055, DA9055_REG_ALARM_Y);
+	if (ret < 0) {
+		dev_err(da9055->dev, "Failed to read ALM: %d\n", ret);
+		return ret;
+	}
+	ret &= DA9055_RTC_ALM_EN;
+	return (ret > 0) ? 1 : 0;
+}
+
+static int da9055_rtc_read_time(struct device *dev, struct rtc_time *rtc_tm)
+{
+	struct da9055_rtc *rtc = dev_get_drvdata(dev);
+	uint8_t v[6];
+	int ret;
+
+	ret = da9055_reg_read(rtc->da9055, DA9055_REG_COUNT_S);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Registers are only valid when RTC_READ
+	 * status bit is asserted
+	 */
+	if (!(ret & DA9055_RTC_READ))
+		return -EBUSY;
+
+	ret = da9055_group_read(rtc->da9055, DA9055_REG_COUNT_S, 6, v);
+	if (ret < 0) {
+		dev_err(rtc->da9055->dev, "Failed to read RTC time : %d\n",
+			ret);
+		return ret;
+	}
+
+	rtc_tm->tm_year = (v[5] & DA9055_RTC_YEAR) + 100;
+	rtc_tm->tm_mon  = (v[4] & DA9055_RTC_MONTH) - 1;
+	rtc_tm->tm_mday = v[3] & DA9055_RTC_DAY;
+	rtc_tm->tm_hour = v[2] & DA9055_RTC_HOUR;
+	rtc_tm->tm_min  = v[1] & DA9055_RTC_MIN;
+	rtc_tm->tm_sec  = v[0] & DA9055_RTC_SEC;
+
+	return 0;
+}
+
+static int da9055_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct da9055_rtc *rtc;
+	uint8_t v[6];
+
+	rtc = dev_get_drvdata(dev);
+
+	v[0] = tm->tm_sec;
+	v[1] = tm->tm_min;
+	v[2] = tm->tm_hour;
+	v[3] = tm->tm_mday;
+	v[4] = tm->tm_mon + 1;
+	v[5] = tm->tm_year - 100;
+
+	return da9055_group_write(rtc->da9055, DA9055_REG_COUNT_S, 6, v);
+}
+
+static int da9055_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	int ret;
+	struct rtc_time *tm = &alrm->time;
+	struct da9055_rtc *rtc = dev_get_drvdata(dev);
+
+	ret = da9055_read_alarm(rtc->da9055, tm);
+
+	if (ret)
+		return ret;
+
+	alrm->enabled = da9055_rtc_get_alarm_status(rtc->da9055);
+
+	return 0;
+}
+
+static int da9055_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	int ret;
+	struct rtc_time *tm = &alrm->time;
+	struct da9055_rtc *rtc = dev_get_drvdata(dev);
+
+	ret = da9055_rtc_enable_alarm(rtc, 0);
+	if (ret < 0)
+		return ret;
+
+	ret = da9055_set_alarm(rtc->da9055, tm);
+	if (ret)
+		return ret;
+
+	ret = da9055_rtc_enable_alarm(rtc, 1);
+
+	return ret;
+}
+
+static int da9055_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct da9055_rtc *rtc = dev_get_drvdata(dev);
+
+	return da9055_rtc_enable_alarm(rtc, enabled);
+}
+
+static const struct rtc_class_ops da9055_rtc_ops = {
+	.read_time	= da9055_rtc_read_time,
+	.set_time	= da9055_rtc_set_time,
+	.read_alarm	= da9055_rtc_read_alarm,
+	.set_alarm	= da9055_rtc_set_alarm,
+	.alarm_irq_enable = da9055_rtc_alarm_irq_enable,
+};
+
+static int da9055_rtc_device_init(struct da9055 *da9055,
+					struct da9055_pdata *pdata)
+{
+	int ret;
+
+	/* Enable RTC and the internal Crystal */
+	ret = da9055_reg_update(da9055, DA9055_REG_CONTROL_B,
+				DA9055_RTC_EN, DA9055_RTC_EN);
+	if (ret < 0)
+		return ret;
+	ret = da9055_reg_update(da9055, DA9055_REG_EN_32K,
+				DA9055_CRYSTAL_EN, DA9055_CRYSTAL_EN);
+	if (ret < 0)
+		return ret;
+
+	/* Enable RTC in Power Down mode */
+	ret = da9055_reg_update(da9055, DA9055_REG_CONTROL_B,
+				DA9055_RTC_MODE_PD, DA9055_RTC_MODE_PD);
+	if (ret < 0)
+		return ret;
+
+	/* Enable RTC in Reset mode */
+	if (pdata && pdata->reset_enable) {
+		ret = da9055_reg_update(da9055, DA9055_REG_CONTROL_B,
+					DA9055_RTC_MODE_SD,
+					DA9055_RTC_MODE_SD <<
+					DA9055_RTC_MODE_SD_SHIFT);
+		if (ret < 0)
+			return ret;
+	}
+
+	/* Disable the RTC TICK ALM */
+	ret = da9055_reg_update(da9055, DA9055_REG_ALARM_MO,
+				DA9055_RTC_TICK_WAKE_MASK, 0);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int da9055_rtc_probe(struct platform_device *pdev)
+{
+	struct da9055_rtc *rtc;
+	struct da9055_pdata *pdata = NULL;
+	int ret, alm_irq;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(struct da9055_rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->da9055 = dev_get_drvdata(pdev->dev.parent);
+	pdata = dev_get_platdata(rtc->da9055->dev);
+	platform_set_drvdata(pdev, rtc);
+
+	ret = da9055_rtc_device_init(rtc->da9055, pdata);
+	if (ret < 0)
+		goto err_rtc;
+
+	ret = da9055_reg_read(rtc->da9055, DA9055_REG_ALARM_Y);
+	if (ret < 0)
+		goto err_rtc;
+
+	if (ret & DA9055_RTC_ALM_EN)
+		rtc->alarm_enable = 1;
+
+	device_init_wakeup(&pdev->dev, true);
+
+	rtc->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
+					&da9055_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc->rtc)) {
+		ret = PTR_ERR(rtc->rtc);
+		goto err_rtc;
+	}
+
+	alm_irq = platform_get_irq_byname(pdev, "ALM");
+	if (alm_irq < 0)
+		return alm_irq;
+
+	ret = devm_request_threaded_irq(&pdev->dev, alm_irq, NULL,
+					da9055_rtc_alm_irq,
+					IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
+					"ALM", rtc);
+	if (ret != 0)
+		dev_err(rtc->da9055->dev, "irq registration failed: %d\n", ret);
+
+err_rtc:
+	return ret;
+
+}
+
+#ifdef CONFIG_PM
+/* Turn off the alarm if it should not be a wake source. */
+static int da9055_rtc_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct da9055_rtc *rtc = dev_get_drvdata(&pdev->dev);
+	int ret;
+
+	if (!device_may_wakeup(&pdev->dev)) {
+		/* Disable the ALM IRQ */
+		ret = da9055_rtc_enable_alarm(rtc, 0);
+		if (ret < 0)
+			dev_err(&pdev->dev, "Failed to disable RTC ALM\n");
+	}
+
+	return 0;
+}
+
+/* Enable the alarm if it should be enabled (in case it was disabled to
+ * prevent use as a wake source).
+ */
+static int da9055_rtc_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct da9055_rtc *rtc = dev_get_drvdata(&pdev->dev);
+	int ret;
+
+	if (!device_may_wakeup(&pdev->dev)) {
+		if (rtc->alarm_enable) {
+			ret = da9055_rtc_enable_alarm(rtc, 1);
+			if (ret < 0)
+				dev_err(&pdev->dev,
+					"Failed to restart RTC ALM\n");
+		}
+	}
+
+	return 0;
+}
+
+/* Unconditionally disable the alarm */
+static int da9055_rtc_freeze(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct da9055_rtc *rtc = dev_get_drvdata(&pdev->dev);
+	int ret;
+
+	ret = da9055_rtc_enable_alarm(rtc, 0);
+	if (ret < 0)
+		dev_err(&pdev->dev, "Failed to freeze RTC ALMs\n");
+
+	return 0;
+
+}
+#else
+#define da9055_rtc_suspend NULL
+#define da9055_rtc_resume NULL
+#define da9055_rtc_freeze NULL
+#endif
+
+static const struct dev_pm_ops da9055_rtc_pm_ops = {
+	.suspend = da9055_rtc_suspend,
+	.resume = da9055_rtc_resume,
+
+	.freeze = da9055_rtc_freeze,
+	.thaw = da9055_rtc_resume,
+	.restore = da9055_rtc_resume,
+
+	.poweroff = da9055_rtc_suspend,
+};
+
+static struct platform_driver da9055_rtc_driver = {
+	.probe  = da9055_rtc_probe,
+	.driver = {
+		.name   = "da9055-rtc",
+		.pm = &da9055_rtc_pm_ops,
+	},
+};
+
+module_platform_driver(da9055_rtc_driver);
+
+MODULE_AUTHOR("David Dajun Chen <dchen@diasemi.com>");
+MODULE_DESCRIPTION("RTC driver for Dialog DA9055 PMIC");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:da9055-rtc");