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, 327 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-tps6586x.c b/drivers/rtc/rtc-tps6586x.c
new file mode 100644
index 000000000..54c8429b1
--- /dev/null
+++ b/drivers/rtc/rtc-tps6586x.c
@@ -0,0 +1,327 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * rtc-tps6586x.c: RTC driver for TI PMIC TPS6586X
+ *
+ * Copyright (c) 2012, NVIDIA Corporation.
+ *
+ * Author: Laxman Dewangan <ldewangan@nvidia.com>
+ */
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/irq.h>
+#include <linux/kernel.h>
+#include <linux/mfd/tps6586x.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pm_runtime.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+
+#define RTC_CTRL			0xc0
+#define POR_RESET_N			BIT(7)
+#define OSC_SRC_SEL			BIT(6)
+#define RTC_ENABLE			BIT(5)	/* enables alarm */
+#define RTC_BUF_ENABLE			BIT(4)	/* 32 KHz buffer enable */
+#define PRE_BYPASS			BIT(3)	/* 0=1KHz or 1=32KHz updates */
+#define CL_SEL_MASK			(BIT(2)|BIT(1))
+#define CL_SEL_POS			1
+#define RTC_ALARM1_HI			0xc1
+#define RTC_COUNT4			0xc6
+
+/* start a PMU RTC access by reading the register prior to the RTC_COUNT4 */
+#define RTC_COUNT4_DUMMYREAD		0xc5
+
+/*only 14-bits width in second*/
+#define ALM1_VALID_RANGE_IN_SEC		0x3FFF
+
+#define TPS6586X_RTC_CL_SEL_1_5PF	0x0
+#define TPS6586X_RTC_CL_SEL_6_5PF	0x1
+#define TPS6586X_RTC_CL_SEL_7_5PF	0x2
+#define TPS6586X_RTC_CL_SEL_12_5PF	0x3
+
+struct tps6586x_rtc {
+	struct device		*dev;
+	struct rtc_device	*rtc;
+	int			irq;
+	bool			irq_en;
+};
+
+static inline struct device *to_tps6586x_dev(struct device *dev)
+{
+	return dev->parent;
+}
+
+static int tps6586x_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct device *tps_dev = to_tps6586x_dev(dev);
+	unsigned long long ticks = 0;
+	time64_t seconds;
+	u8 buff[6];
+	int ret;
+	int i;
+
+	ret = tps6586x_reads(tps_dev, RTC_COUNT4_DUMMYREAD, sizeof(buff), buff);
+	if (ret < 0) {
+		dev_err(dev, "read counter failed with err %d\n", ret);
+		return ret;
+	}
+
+	for (i = 1; i < sizeof(buff); i++) {
+		ticks <<= 8;
+		ticks |= buff[i];
+	}
+
+	seconds = ticks >> 10;
+	rtc_time64_to_tm(seconds, tm);
+
+	return 0;
+}
+
+static int tps6586x_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct device *tps_dev = to_tps6586x_dev(dev);
+	unsigned long long ticks;
+	time64_t seconds;
+	u8 buff[5];
+	int ret;
+
+	seconds = rtc_tm_to_time64(tm);
+
+	ticks = (unsigned long long)seconds << 10;
+	buff[0] = (ticks >> 32) & 0xff;
+	buff[1] = (ticks >> 24) & 0xff;
+	buff[2] = (ticks >> 16) & 0xff;
+	buff[3] = (ticks >> 8) & 0xff;
+	buff[4] = ticks & 0xff;
+
+	/* Disable RTC before changing time */
+	ret = tps6586x_clr_bits(tps_dev, RTC_CTRL, RTC_ENABLE);
+	if (ret < 0) {
+		dev_err(dev, "failed to clear RTC_ENABLE\n");
+		return ret;
+	}
+
+	ret = tps6586x_writes(tps_dev, RTC_COUNT4, sizeof(buff), buff);
+	if (ret < 0) {
+		dev_err(dev, "failed to program new time\n");
+		return ret;
+	}
+
+	/* Enable RTC */
+	ret = tps6586x_set_bits(tps_dev, RTC_CTRL, RTC_ENABLE);
+	if (ret < 0) {
+		dev_err(dev, "failed to set RTC_ENABLE\n");
+		return ret;
+	}
+	return 0;
+}
+
+static int tps6586x_rtc_alarm_irq_enable(struct device *dev,
+			 unsigned int enabled)
+{
+	struct tps6586x_rtc *rtc = dev_get_drvdata(dev);
+
+	if (enabled && !rtc->irq_en) {
+		enable_irq(rtc->irq);
+		rtc->irq_en = true;
+	} else if (!enabled && rtc->irq_en)  {
+		disable_irq(rtc->irq);
+		rtc->irq_en = false;
+	}
+	return 0;
+}
+
+static int tps6586x_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct device *tps_dev = to_tps6586x_dev(dev);
+	time64_t seconds;
+	unsigned long ticks;
+	unsigned long rtc_current_time;
+	unsigned long long rticks = 0;
+	u8 buff[3];
+	u8 rbuff[6];
+	int ret;
+	int i;
+
+	seconds = rtc_tm_to_time64(&alrm->time);
+
+	ret = tps6586x_rtc_alarm_irq_enable(dev, alrm->enabled);
+	if (ret < 0) {
+		dev_err(dev, "can't set alarm irq, err %d\n", ret);
+		return ret;
+	}
+
+	ret = tps6586x_reads(tps_dev, RTC_COUNT4_DUMMYREAD,
+			sizeof(rbuff), rbuff);
+	if (ret < 0) {
+		dev_err(dev, "read counter failed with err %d\n", ret);
+		return ret;
+	}
+
+	for (i = 1; i < sizeof(rbuff); i++) {
+		rticks <<= 8;
+		rticks |= rbuff[i];
+	}
+
+	rtc_current_time = rticks >> 10;
+	if ((seconds - rtc_current_time) > ALM1_VALID_RANGE_IN_SEC)
+		seconds = rtc_current_time - 1;
+
+	ticks = (unsigned long long)seconds << 10;
+	buff[0] = (ticks >> 16) & 0xff;
+	buff[1] = (ticks >> 8) & 0xff;
+	buff[2] = ticks & 0xff;
+
+	ret = tps6586x_writes(tps_dev, RTC_ALARM1_HI, sizeof(buff), buff);
+	if (ret)
+		dev_err(dev, "programming alarm failed with err %d\n", ret);
+
+	return ret;
+}
+
+static int tps6586x_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct device *tps_dev = to_tps6586x_dev(dev);
+	unsigned long ticks;
+	time64_t seconds;
+	u8 buff[3];
+	int ret;
+
+	ret = tps6586x_reads(tps_dev, RTC_ALARM1_HI, sizeof(buff), buff);
+	if (ret) {
+		dev_err(dev, "read RTC_ALARM1_HI failed with err %d\n", ret);
+		return ret;
+	}
+
+	ticks = (buff[0] << 16) | (buff[1] << 8) | buff[2];
+	seconds = ticks >> 10;
+
+	rtc_time64_to_tm(seconds, &alrm->time);
+	return 0;
+}
+
+static const struct rtc_class_ops tps6586x_rtc_ops = {
+	.read_time	= tps6586x_rtc_read_time,
+	.set_time	= tps6586x_rtc_set_time,
+	.set_alarm	= tps6586x_rtc_set_alarm,
+	.read_alarm	= tps6586x_rtc_read_alarm,
+	.alarm_irq_enable = tps6586x_rtc_alarm_irq_enable,
+};
+
+static irqreturn_t tps6586x_rtc_irq(int irq, void *data)
+{
+	struct tps6586x_rtc *rtc = data;
+
+	rtc_update_irq(rtc->rtc, 1, RTC_IRQF | RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static int tps6586x_rtc_probe(struct platform_device *pdev)
+{
+	struct device *tps_dev = to_tps6586x_dev(&pdev->dev);
+	struct tps6586x_rtc *rtc;
+	int ret;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->dev = &pdev->dev;
+	rtc->irq = platform_get_irq(pdev, 0);
+
+	/* 1 kHz tick mode, enable tick counting */
+	ret = tps6586x_update(tps_dev, RTC_CTRL,
+		RTC_ENABLE | OSC_SRC_SEL |
+		((TPS6586X_RTC_CL_SEL_1_5PF << CL_SEL_POS) & CL_SEL_MASK),
+		RTC_ENABLE | OSC_SRC_SEL | PRE_BYPASS | CL_SEL_MASK);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "unable to start counter\n");
+		return ret;
+	}
+
+	device_init_wakeup(&pdev->dev, true);
+
+	platform_set_drvdata(pdev, rtc);
+	rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc->rtc)) {
+		ret = PTR_ERR(rtc->rtc);
+		goto fail_rtc_register;
+	}
+
+	rtc->rtc->ops = &tps6586x_rtc_ops;
+	rtc->rtc->range_max = (1ULL << 30) - 1; /* 30-bit seconds */
+	rtc->rtc->alarm_offset_max = ALM1_VALID_RANGE_IN_SEC;
+	rtc->rtc->start_secs = mktime64(2009, 1, 1, 0, 0, 0);
+	rtc->rtc->set_start_time = true;
+
+	irq_set_status_flags(rtc->irq, IRQ_NOAUTOEN);
+
+	ret = devm_request_threaded_irq(&pdev->dev, rtc->irq, NULL,
+				tps6586x_rtc_irq,
+				IRQF_ONESHOT,
+				dev_name(&pdev->dev), rtc);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "request IRQ(%d) failed with ret %d\n",
+				rtc->irq, ret);
+		goto fail_rtc_register;
+	}
+
+	ret = devm_rtc_register_device(rtc->rtc);
+	if (ret)
+		goto fail_rtc_register;
+
+	return 0;
+
+fail_rtc_register:
+	tps6586x_update(tps_dev, RTC_CTRL, 0,
+		RTC_ENABLE | OSC_SRC_SEL | PRE_BYPASS | CL_SEL_MASK);
+	return ret;
+};
+
+static void tps6586x_rtc_remove(struct platform_device *pdev)
+{
+	struct device *tps_dev = to_tps6586x_dev(&pdev->dev);
+
+	tps6586x_update(tps_dev, RTC_CTRL, 0,
+		RTC_ENABLE | OSC_SRC_SEL | PRE_BYPASS | CL_SEL_MASK);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int tps6586x_rtc_suspend(struct device *dev)
+{
+	struct tps6586x_rtc *rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(rtc->irq);
+	return 0;
+}
+
+static int tps6586x_rtc_resume(struct device *dev)
+{
+	struct tps6586x_rtc *rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(rtc->irq);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(tps6586x_pm_ops, tps6586x_rtc_suspend,
+			tps6586x_rtc_resume);
+
+static struct platform_driver tps6586x_rtc_driver = {
+	.driver	= {
+		.name	= "tps6586x-rtc",
+		.pm	= &tps6586x_pm_ops,
+	},
+	.probe	= tps6586x_rtc_probe,
+	.remove = tps6586x_rtc_remove,
+};
+module_platform_driver(tps6586x_rtc_driver);
+
+MODULE_ALIAS("platform:tps6586x-rtc");
+MODULE_DESCRIPTION("TI TPS6586x RTC driver");
+MODULE_AUTHOR("Laxman dewangan <ldewangan@nvidia.com>");
+MODULE_LICENSE("GPL v2");