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, 290 insertions, 0 deletions

diff --git a/drivers/regulator/stm32-vrefbuf.c b/drivers/regulator/stm32-vrefbuf.c
new file mode 100644
index 000000000..9e391206f
--- /dev/null
+++ b/drivers/regulator/stm32-vrefbuf.c
@@ -0,0 +1,290 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) STMicroelectronics 2017
+ *
+ * Author: Fabrice Gasnier <fabrice.gasnier@st.com>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/clk.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/driver.h>
+#include <linux/regulator/of_regulator.h>
+#include <linux/pm_runtime.h>
+
+/* STM32 VREFBUF registers */
+#define STM32_VREFBUF_CSR		0x00
+
+/* STM32 VREFBUF CSR bitfields */
+#define STM32_VRS			GENMASK(6, 4)
+#define STM32_VRR			BIT(3)
+#define STM32_HIZ			BIT(1)
+#define STM32_ENVR			BIT(0)
+
+#define STM32_VREFBUF_AUTO_SUSPEND_DELAY_MS	10
+
+struct stm32_vrefbuf {
+	void __iomem *base;
+	struct clk *clk;
+	struct device *dev;
+};
+
+static const unsigned int stm32_vrefbuf_voltages[] = {
+	/* Matches resp. VRS = 000b, 001b, 010b, 011b */
+	2500000, 2048000, 1800000, 1500000,
+};
+
+static int stm32_vrefbuf_enable(struct regulator_dev *rdev)
+{
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+	u32 val;
+	int ret;
+
+	ret = pm_runtime_resume_and_get(priv->dev);
+	if (ret < 0)
+		return ret;
+
+	val = readl_relaxed(priv->base + STM32_VREFBUF_CSR);
+	val = (val & ~STM32_HIZ) | STM32_ENVR;
+	writel_relaxed(val, priv->base + STM32_VREFBUF_CSR);
+
+	/*
+	 * Vrefbuf startup time depends on external capacitor: wait here for
+	 * VRR to be set. That means output has reached expected value.
+	 * ~650us sleep should be enough for caps up to 1.5uF. Use 10ms as
+	 * arbitrary timeout.
+	 */
+	ret = readl_poll_timeout(priv->base + STM32_VREFBUF_CSR, val,
+				 val & STM32_VRR, 650, 10000);
+	if (ret) {
+		dev_err(&rdev->dev, "stm32 vrefbuf timed out!\n");
+		val = readl_relaxed(priv->base + STM32_VREFBUF_CSR);
+		val = (val & ~STM32_ENVR) | STM32_HIZ;
+		writel_relaxed(val, priv->base + STM32_VREFBUF_CSR);
+	}
+
+	pm_runtime_put_autosuspend(priv->dev);
+
+	return ret;
+}
+
+static int stm32_vrefbuf_disable(struct regulator_dev *rdev)
+{
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+	u32 val;
+	int ret;
+
+	ret = pm_runtime_resume_and_get(priv->dev);
+	if (ret < 0)
+		return ret;
+
+	val = readl_relaxed(priv->base + STM32_VREFBUF_CSR);
+	val &= ~STM32_ENVR;
+	writel_relaxed(val, priv->base + STM32_VREFBUF_CSR);
+
+	pm_runtime_put_autosuspend(priv->dev);
+
+	return 0;
+}
+
+static int stm32_vrefbuf_is_enabled(struct regulator_dev *rdev)
+{
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+	int ret;
+
+	ret = pm_runtime_resume_and_get(priv->dev);
+	if (ret < 0)
+		return ret;
+
+	ret = readl_relaxed(priv->base + STM32_VREFBUF_CSR) & STM32_ENVR;
+
+	pm_runtime_put_autosuspend(priv->dev);
+
+	return ret;
+}
+
+static int stm32_vrefbuf_set_voltage_sel(struct regulator_dev *rdev,
+					 unsigned sel)
+{
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+	u32 val;
+	int ret;
+
+	ret = pm_runtime_resume_and_get(priv->dev);
+	if (ret < 0)
+		return ret;
+
+	val = readl_relaxed(priv->base + STM32_VREFBUF_CSR);
+	val = (val & ~STM32_VRS) | FIELD_PREP(STM32_VRS, sel);
+	writel_relaxed(val, priv->base + STM32_VREFBUF_CSR);
+
+	pm_runtime_put_autosuspend(priv->dev);
+
+	return 0;
+}
+
+static int stm32_vrefbuf_get_voltage_sel(struct regulator_dev *rdev)
+{
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+	u32 val;
+	int ret;
+
+	ret = pm_runtime_resume_and_get(priv->dev);
+	if (ret < 0)
+		return ret;
+
+	val = readl_relaxed(priv->base + STM32_VREFBUF_CSR);
+	ret = FIELD_GET(STM32_VRS, val);
+
+	pm_runtime_put_autosuspend(priv->dev);
+
+	return ret;
+}
+
+static const struct regulator_ops stm32_vrefbuf_volt_ops = {
+	.enable		= stm32_vrefbuf_enable,
+	.disable	= stm32_vrefbuf_disable,
+	.is_enabled	= stm32_vrefbuf_is_enabled,
+	.get_voltage_sel = stm32_vrefbuf_get_voltage_sel,
+	.set_voltage_sel = stm32_vrefbuf_set_voltage_sel,
+	.list_voltage	= regulator_list_voltage_table,
+};
+
+static const struct regulator_desc stm32_vrefbuf_regu = {
+	.name = "vref",
+	.supply_name = "vdda",
+	.volt_table = stm32_vrefbuf_voltages,
+	.n_voltages = ARRAY_SIZE(stm32_vrefbuf_voltages),
+	.ops = &stm32_vrefbuf_volt_ops,
+	.off_on_delay = 1000,
+	.type = REGULATOR_VOLTAGE,
+	.owner = THIS_MODULE,
+};
+
+static int stm32_vrefbuf_probe(struct platform_device *pdev)
+{
+	struct stm32_vrefbuf *priv;
+	struct regulator_config config = { };
+	struct regulator_dev *rdev;
+	int ret;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	priv->dev = &pdev->dev;
+
+	priv->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	priv->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(priv->clk))
+		return PTR_ERR(priv->clk);
+
+	pm_runtime_get_noresume(&pdev->dev);
+	pm_runtime_set_active(&pdev->dev);
+	pm_runtime_set_autosuspend_delay(&pdev->dev,
+					 STM32_VREFBUF_AUTO_SUSPEND_DELAY_MS);
+	pm_runtime_use_autosuspend(&pdev->dev);
+	pm_runtime_enable(&pdev->dev);
+
+	ret = clk_prepare_enable(priv->clk);
+	if (ret) {
+		dev_err(&pdev->dev, "clk prepare failed with error %d\n", ret);
+		goto err_pm_stop;
+	}
+
+	config.dev = &pdev->dev;
+	config.driver_data = priv;
+	config.of_node = pdev->dev.of_node;
+	config.init_data = of_get_regulator_init_data(&pdev->dev,
+						      pdev->dev.of_node,
+						      &stm32_vrefbuf_regu);
+
+	rdev = regulator_register(&pdev->dev, &stm32_vrefbuf_regu, &config);
+	if (IS_ERR(rdev)) {
+		ret = PTR_ERR(rdev);
+		dev_err(&pdev->dev, "register failed with error %d\n", ret);
+		goto err_clk_dis;
+	}
+	platform_set_drvdata(pdev, rdev);
+
+	pm_runtime_put_autosuspend(&pdev->dev);
+
+	return 0;
+
+err_clk_dis:
+	clk_disable_unprepare(priv->clk);
+err_pm_stop:
+	pm_runtime_disable(&pdev->dev);
+	pm_runtime_set_suspended(&pdev->dev);
+	pm_runtime_put_noidle(&pdev->dev);
+
+	return ret;
+}
+
+static void stm32_vrefbuf_remove(struct platform_device *pdev)
+{
+	struct regulator_dev *rdev = platform_get_drvdata(pdev);
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+
+	pm_runtime_get_sync(&pdev->dev);
+	regulator_unregister(rdev);
+	clk_disable_unprepare(priv->clk);
+	pm_runtime_disable(&pdev->dev);
+	pm_runtime_set_suspended(&pdev->dev);
+	pm_runtime_put_noidle(&pdev->dev);
+};
+
+static int __maybe_unused stm32_vrefbuf_runtime_suspend(struct device *dev)
+{
+	struct regulator_dev *rdev = dev_get_drvdata(dev);
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+
+	clk_disable_unprepare(priv->clk);
+
+	return 0;
+}
+
+static int __maybe_unused stm32_vrefbuf_runtime_resume(struct device *dev)
+{
+	struct regulator_dev *rdev = dev_get_drvdata(dev);
+	struct stm32_vrefbuf *priv = rdev_get_drvdata(rdev);
+
+	return clk_prepare_enable(priv->clk);
+}
+
+static const struct dev_pm_ops stm32_vrefbuf_pm_ops = {
+	SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
+				pm_runtime_force_resume)
+	SET_RUNTIME_PM_OPS(stm32_vrefbuf_runtime_suspend,
+			   stm32_vrefbuf_runtime_resume,
+			   NULL)
+};
+
+static const struct of_device_id __maybe_unused stm32_vrefbuf_of_match[] = {
+	{ .compatible = "st,stm32-vrefbuf", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, stm32_vrefbuf_of_match);
+
+static struct platform_driver stm32_vrefbuf_driver = {
+	.probe = stm32_vrefbuf_probe,
+	.remove = stm32_vrefbuf_remove,
+	.driver = {
+		.name  = "stm32-vrefbuf",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = of_match_ptr(stm32_vrefbuf_of_match),
+		.pm = &stm32_vrefbuf_pm_ops,
+	},
+};
+module_platform_driver(stm32_vrefbuf_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Fabrice Gasnier <fabrice.gasnier@st.com>");
+MODULE_DESCRIPTION("STMicroelectronics STM32 VREFBUF driver");
+MODULE_ALIAS("platform:stm32-vrefbuf");