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, 385 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-s32g.c b/drivers/rtc/rtc-s32g.c
new file mode 100644
index 000000000..3a0818e97
--- /dev/null
+++ b/drivers/rtc/rtc-s32g.c
@@ -0,0 +1,385 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 2025 NXP
+ */
+
+#include <linux/bitfield.h>
+#include <linux/clk.h>
+#include <linux/iopoll.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#define RTCC_OFFSET	0x4ul
+#define RTCS_OFFSET	0x8ul
+#define APIVAL_OFFSET	0x10ul
+
+/* RTCC fields */
+#define RTCC_CNTEN				BIT(31)
+#define RTCC_APIEN				BIT(15)
+#define RTCC_APIIE				BIT(14)
+#define RTCC_CLKSEL_MASK		GENMASK(13, 12)
+#define RTCC_DIV512EN			BIT(11)
+#define RTCC_DIV32EN			BIT(10)
+
+/* RTCS fields */
+#define RTCS_INV_API	BIT(17)
+#define RTCS_APIF		BIT(13)
+
+#define APIVAL_MAX_VAL		GENMASK(31, 0)
+#define RTC_SYNCH_TIMEOUT	(100 * USEC_PER_MSEC)
+
+/*
+ * S32G2 and S32G3 SoCs have RTC clock source1 reserved and
+ * should not be used.
+ */
+#define RTC_CLK_SRC1_RESERVED		BIT(1)
+
+/*
+ * S32G RTC module has a 512 value and a 32 value hardware frequency
+ * divisors (DIV512 and DIV32) which could be used to achieve higher
+ * counter ranges by lowering the RTC frequency.
+ */
+enum {
+	DIV1 = 1,
+	DIV32 = 32,
+	DIV512 = 512,
+	DIV512_32 = 16384
+};
+
+static const char *const rtc_clk_src[] = {
+	"source0",
+	"source1",
+	"source2",
+	"source3"
+};
+
+struct rtc_priv {
+	struct rtc_device *rdev;
+	void __iomem *rtc_base;
+	struct clk *ipg;
+	struct clk *clk_src;
+	const struct rtc_soc_data *rtc_data;
+	u64 rtc_hz;
+	time64_t sleep_sec;
+	int irq;
+	u32 clk_src_idx;
+};
+
+struct rtc_soc_data {
+	u32 clk_div;
+	u32 reserved_clk_mask;
+};
+
+static const struct rtc_soc_data rtc_s32g2_data = {
+	.clk_div = DIV512_32,
+	.reserved_clk_mask = RTC_CLK_SRC1_RESERVED,
+};
+
+static irqreturn_t s32g_rtc_handler(int irq, void *dev)
+{
+	struct rtc_priv *priv = platform_get_drvdata(dev);
+	u32 status;
+
+	status = readl(priv->rtc_base + RTCS_OFFSET);
+
+	if (status & RTCS_APIF) {
+		writel(0x0, priv->rtc_base + APIVAL_OFFSET);
+		writel(status | RTCS_APIF, priv->rtc_base + RTCS_OFFSET);
+	}
+
+	rtc_update_irq(priv->rdev, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * The function is not really getting time from the RTC since the S32G RTC
+ * has several limitations. Thus, to setup alarm use system time.
+ */
+static int s32g_rtc_read_time(struct device *dev,
+			      struct rtc_time *tm)
+{
+	struct rtc_priv *priv = dev_get_drvdata(dev);
+	time64_t sec;
+
+	if (check_add_overflow(ktime_get_real_seconds(),
+			       priv->sleep_sec, &sec))
+		return -ERANGE;
+
+	rtc_time64_to_tm(sec, tm);
+
+	return 0;
+}
+
+static int s32g_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rtc_priv *priv = dev_get_drvdata(dev);
+	u32 rtcc, rtcs;
+
+	rtcc = readl(priv->rtc_base + RTCC_OFFSET);
+	rtcs = readl(priv->rtc_base + RTCS_OFFSET);
+
+	alrm->enabled = rtcc & RTCC_APIIE;
+	if (alrm->enabled)
+		alrm->pending = !(rtcs & RTCS_APIF);
+
+	return 0;
+}
+
+static int s32g_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct rtc_priv *priv = dev_get_drvdata(dev);
+	u32 rtcc;
+
+	/* RTC API functionality is used both for triggering interrupts
+	 * and as a wakeup event. Hence it should always be enabled.
+	 */
+	rtcc = readl(priv->rtc_base + RTCC_OFFSET);
+	rtcc |= RTCC_APIEN | RTCC_APIIE;
+	writel(rtcc, priv->rtc_base + RTCC_OFFSET);
+
+	return 0;
+}
+
+static int s32g_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rtc_priv *priv = dev_get_drvdata(dev);
+	unsigned long long cycles;
+	long long t_offset;
+	time64_t alrm_time;
+	u32 rtcs;
+	int ret;
+
+	alrm_time = rtc_tm_to_time64(&alrm->time);
+	t_offset = alrm_time - ktime_get_real_seconds() - priv->sleep_sec;
+	if (t_offset < 0)
+		return -ERANGE;
+
+	cycles = t_offset * priv->rtc_hz;
+	if (cycles > APIVAL_MAX_VAL)
+		return -ERANGE;
+
+	/* APIVAL could have been reset from the IRQ handler.
+	 * Hence, we wait in case there is a synchronization process.
+	 */
+	ret = read_poll_timeout(readl, rtcs, !(rtcs & RTCS_INV_API),
+				0, RTC_SYNCH_TIMEOUT, false, priv->rtc_base + RTCS_OFFSET);
+	if (ret)
+		return ret;
+
+	writel(cycles, priv->rtc_base + APIVAL_OFFSET);
+
+	return read_poll_timeout(readl, rtcs, !(rtcs & RTCS_INV_API),
+				0, RTC_SYNCH_TIMEOUT, false, priv->rtc_base + RTCS_OFFSET);
+}
+
+/*
+ * Disable the 32-bit free running counter.
+ * This allows Clock Source and Divisors selection
+ * to be performed without causing synchronization issues.
+ */
+static void s32g_rtc_disable(struct rtc_priv *priv)
+{
+	u32 rtcc = readl(priv->rtc_base + RTCC_OFFSET);
+
+	rtcc &= ~RTCC_CNTEN;
+	writel(rtcc, priv->rtc_base + RTCC_OFFSET);
+}
+
+static void s32g_rtc_enable(struct rtc_priv *priv)
+{
+	u32 rtcc = readl(priv->rtc_base + RTCC_OFFSET);
+
+	rtcc |= RTCC_CNTEN;
+	writel(rtcc, priv->rtc_base + RTCC_OFFSET);
+}
+
+static int rtc_clk_src_setup(struct rtc_priv *priv)
+{
+	u32 rtcc;
+
+	rtcc = FIELD_PREP(RTCC_CLKSEL_MASK, priv->clk_src_idx);
+
+	switch (priv->rtc_data->clk_div) {
+	case DIV512_32:
+		rtcc |= RTCC_DIV512EN;
+		rtcc |= RTCC_DIV32EN;
+		break;
+	case DIV512:
+		rtcc |= RTCC_DIV512EN;
+		break;
+	case DIV32:
+		rtcc |= RTCC_DIV32EN;
+		break;
+	case DIV1:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	rtcc |= RTCC_APIEN | RTCC_APIIE;
+	/*
+	 * Make sure the CNTEN is 0 before we configure
+	 * the clock source and dividers.
+	 */
+	s32g_rtc_disable(priv);
+	writel(rtcc, priv->rtc_base + RTCC_OFFSET);
+	s32g_rtc_enable(priv);
+
+	return 0;
+}
+
+static const struct rtc_class_ops rtc_ops = {
+	.read_time = s32g_rtc_read_time,
+	.read_alarm = s32g_rtc_read_alarm,
+	.set_alarm = s32g_rtc_set_alarm,
+	.alarm_irq_enable = s32g_rtc_alarm_irq_enable,
+};
+
+static int rtc_clk_dts_setup(struct rtc_priv *priv,
+			     struct device *dev)
+{
+	u32 i;
+
+	priv->ipg = devm_clk_get_enabled(dev, "ipg");
+	if (IS_ERR(priv->ipg))
+		return dev_err_probe(dev, PTR_ERR(priv->ipg),
+				"Failed to get 'ipg' clock\n");
+
+	for (i = 0; i < ARRAY_SIZE(rtc_clk_src); i++) {
+		if (priv->rtc_data->reserved_clk_mask & BIT(i))
+			return -EOPNOTSUPP;
+
+		priv->clk_src = devm_clk_get_enabled(dev, rtc_clk_src[i]);
+		if (!IS_ERR(priv->clk_src)) {
+			priv->clk_src_idx = i;
+			break;
+		}
+	}
+
+	if (IS_ERR(priv->clk_src))
+		return dev_err_probe(dev, PTR_ERR(priv->clk_src),
+				"Failed to get rtc module clock source\n");
+
+	return 0;
+}
+
+static int s32g_rtc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct rtc_priv *priv;
+	unsigned long rtc_hz;
+	int ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->rtc_data = of_device_get_match_data(dev);
+	if (!priv->rtc_data)
+		return -ENODEV;
+
+	priv->rtc_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->rtc_base))
+		return PTR_ERR(priv->rtc_base);
+
+	device_init_wakeup(dev, true);
+
+	ret = rtc_clk_dts_setup(priv, dev);
+	if (ret)
+		return ret;
+
+	priv->rdev = devm_rtc_allocate_device(dev);
+	if (IS_ERR(priv->rdev))
+		return PTR_ERR(priv->rdev);
+
+	ret = rtc_clk_src_setup(priv);
+	if (ret)
+		return ret;
+
+	priv->irq = platform_get_irq(pdev, 0);
+	if (priv->irq < 0) {
+		ret = priv->irq;
+		goto disable_rtc;
+	}
+
+	rtc_hz = clk_get_rate(priv->clk_src);
+	if (!rtc_hz) {
+		dev_err(dev, "Failed to get RTC frequency\n");
+		ret = -EINVAL;
+		goto disable_rtc;
+	}
+
+	priv->rtc_hz = DIV_ROUND_UP(rtc_hz, priv->rtc_data->clk_div);
+
+	platform_set_drvdata(pdev, priv);
+	priv->rdev->ops = &rtc_ops;
+
+	ret = devm_request_irq(dev, priv->irq,
+			       s32g_rtc_handler, 0, dev_name(dev), pdev);
+	if (ret) {
+		dev_err(dev, "Request interrupt %d failed, error: %d\n",
+			priv->irq, ret);
+		goto disable_rtc;
+	}
+
+	ret = devm_rtc_register_device(priv->rdev);
+	if (ret)
+		goto disable_rtc;
+
+	return 0;
+
+disable_rtc:
+	s32g_rtc_disable(priv);
+	return ret;
+}
+
+static int s32g_rtc_suspend(struct device *dev)
+{
+	struct rtc_priv *priv = dev_get_drvdata(dev);
+	u32 apival = readl(priv->rtc_base + APIVAL_OFFSET);
+
+	if (check_add_overflow(priv->sleep_sec, div64_u64(apival, priv->rtc_hz),
+			       &priv->sleep_sec)) {
+		dev_warn(dev, "Overflow on sleep cycles occurred. Resetting to 0.\n");
+		priv->sleep_sec = 0;
+	}
+
+	return 0;
+}
+
+static int s32g_rtc_resume(struct device *dev)
+{
+	struct rtc_priv *priv = dev_get_drvdata(dev);
+
+	/* The transition from resume to run is a reset event.
+	 * This leads to the RTC registers being reset after resume from
+	 * suspend. It is uncommon, but this behaviour has been observed
+	 * on S32G RTC after issuing a Suspend to RAM operation.
+	 * Thus, reconfigure RTC registers on the resume path.
+	 */
+	return rtc_clk_src_setup(priv);
+}
+
+static const struct of_device_id rtc_dt_ids[] = {
+	{ .compatible = "nxp,s32g2-rtc", .data = &rtc_s32g2_data },
+	{ /* sentinel */ },
+};
+
+static DEFINE_SIMPLE_DEV_PM_OPS(s32g_rtc_pm_ops,
+			 s32g_rtc_suspend, s32g_rtc_resume);
+
+static struct platform_driver s32g_rtc_driver = {
+	.driver = {
+		.name = "s32g-rtc",
+		.pm = pm_sleep_ptr(&s32g_rtc_pm_ops),
+		.of_match_table = rtc_dt_ids,
+	},
+	.probe = s32g_rtc_probe,
+};
+module_platform_driver(s32g_rtc_driver);
+
+MODULE_AUTHOR("NXP");
+MODULE_DESCRIPTION("NXP RTC driver for S32G2/S32G3");
+MODULE_LICENSE("GPL");