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, 215 insertions, 0 deletions

diff --git a/drivers/regulator/rt4803.c b/drivers/regulator/rt4803.c
new file mode 100644
index 000000000..34cd3f249
--- /dev/null
+++ b/drivers/regulator/rt4803.c
@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 Richtek Technology Corp.
+ *
+ * Author: ChiYuan Huang <cy_huang@richtek.com>
+ */
+
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/property.h>
+#include <linux/regmap.h>
+#include <linux/regulator/driver.h>
+#include <linux/regulator/of_regulator.h>
+
+#define RT4803_AUTO_MODE	1
+#define RT4803_FPWM_MODE	2
+
+#define RT4803_REG_CONFIG	0x01
+#define RT4803_REG_VSELL	0x02
+#define RT4803_REG_VSELH	0x03
+#define RT4803_REG_ILIM		0x04
+#define RT4803_REG_STAT		0x05
+
+#define RT4803_MODE_MASK	GENMASK(1, 0)
+#define RT4803_VSEL_MASK	GENMASK(4, 0)
+#define RT4803_ILIM_MASK	GENMASK(3, 0)
+#define RT4803_TSD_MASK		BIT(7)
+#define RT4803_HOTDIE_MASK	BIT(6)
+#define RT4803_FAULT_MASK	BIT(1)
+#define RT4803_PGOOD_MASK	BIT(0)
+
+#define RT4803_VOUT_MINUV	2850000
+#define RT4803_VOUT_STEPUV	50000
+#define RT4803_VOUT_NUM		32
+
+static int rt4803_set_mode(struct regulator_dev *rdev, unsigned int mode)
+{
+	struct regmap *regmap = rdev_get_regmap(rdev);
+	unsigned int modeval;
+
+	switch (mode) {
+	case REGULATOR_MODE_NORMAL:
+		modeval = RT4803_AUTO_MODE;
+		break;
+	case REGULATOR_MODE_FAST:
+		modeval = RT4803_FPWM_MODE;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	modeval <<= ffs(RT4803_MODE_MASK) - 1;
+
+	return regmap_update_bits(regmap, RT4803_REG_CONFIG, RT4803_MODE_MASK, modeval);
+}
+
+static unsigned int rt4803_get_mode(struct regulator_dev *rdev)
+{
+	struct regmap *regmap = rdev_get_regmap(rdev);
+	unsigned int modeval;
+	int ret;
+
+	ret = regmap_read(regmap, RT4803_REG_CONFIG, &modeval);
+	if (ret)
+		return REGULATOR_MODE_INVALID;
+
+	modeval >>= ffs(RT4803_MODE_MASK) - 1;
+
+	switch (modeval) {
+	case RT4803_AUTO_MODE:
+		return REGULATOR_MODE_NORMAL;
+	case RT4803_FPWM_MODE:
+		return REGULATOR_MODE_FAST;
+	default:
+		return REGULATOR_MODE_INVALID;
+	}
+}
+
+static int rt4803_get_error_flags(struct regulator_dev *rdev, unsigned int *flags)
+{
+	struct regmap *regmap = rdev_get_regmap(rdev);
+	unsigned int state, events = 0;
+	int ret;
+
+	ret = regmap_read(regmap, RT4803_REG_STAT, &state);
+	if (ret)
+		return ret;
+
+	if (state & RT4803_PGOOD_MASK)
+		goto out_error_flag;
+
+	if (state & RT4803_FAULT_MASK)
+		events |= REGULATOR_ERROR_FAIL;
+
+	if (state & RT4803_HOTDIE_MASK)
+		events |= REGULATOR_ERROR_OVER_TEMP_WARN;
+
+	if (state & RT4803_TSD_MASK)
+		events |= REGULATOR_ERROR_OVER_TEMP;
+
+out_error_flag:
+	*flags = events;
+	return 0;
+}
+
+static int rt4803_set_suspend_voltage(struct regulator_dev *rdev, int uV)
+{
+	struct regmap *regmap = rdev_get_regmap(rdev);
+	unsigned int reg, vsel;
+
+	if (rdev->desc->vsel_reg == RT4803_REG_VSELL)
+		reg = RT4803_REG_VSELH;
+	else
+		reg = RT4803_REG_VSELL;
+
+	vsel = (uV - rdev->desc->min_uV) / rdev->desc->uV_step;
+	vsel <<= ffs(RT4803_VSEL_MASK) - 1;
+
+	return regmap_update_bits(regmap, reg, RT4803_VSEL_MASK, vsel);
+}
+
+static const struct regulator_ops rt4803_regulator_ops = {
+	.list_voltage = regulator_list_voltage_linear,
+	.set_voltage_sel = regulator_set_voltage_sel_regmap,
+	.get_voltage_sel = regulator_get_voltage_sel_regmap,
+	.set_mode = rt4803_set_mode,
+	.get_mode = rt4803_get_mode,
+	.get_error_flags = rt4803_get_error_flags,
+	.set_suspend_voltage = rt4803_set_suspend_voltage,
+};
+
+static unsigned int rt4803_of_map_mode(unsigned int mode)
+{
+	switch (mode) {
+	case RT4803_AUTO_MODE:
+		return REGULATOR_MODE_NORMAL;
+	case RT4803_FPWM_MODE:
+		return REGULATOR_MODE_FAST;
+	default:
+		return REGULATOR_MODE_INVALID;
+	}
+}
+
+static const struct regmap_config rt4803_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = RT4803_REG_STAT,
+};
+
+static int rt4803_probe(struct i2c_client *i2c)
+{
+	struct device *dev = &i2c->dev;
+	struct regmap *regmap;
+	struct regulator_desc *desc;
+	struct regulator_config cfg = {};
+	struct regulator_dev *rdev;
+	bool vsel_act_high;
+	int ret;
+
+	desc = devm_kzalloc(dev, sizeof(*desc), GFP_KERNEL);
+	if (!desc)
+		return -ENOMEM;
+
+	regmap = devm_regmap_init_i2c(i2c, &rt4803_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap), "Failed to init regmap\n");
+
+	/* Always configure the input current limit to max 5A at initial */
+	ret = regmap_update_bits(regmap, RT4803_REG_ILIM, RT4803_ILIM_MASK, 0xff);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to config ILIM to max\n");
+
+	vsel_act_high = device_property_read_bool(dev, "richtek,vsel-active-high");
+
+	desc->name = "rt4803-regulator";
+	desc->type = REGULATOR_VOLTAGE;
+	desc->owner = THIS_MODULE;
+	desc->ops = &rt4803_regulator_ops;
+	desc->min_uV = RT4803_VOUT_MINUV;
+	desc->uV_step = RT4803_VOUT_STEPUV;
+	desc->n_voltages = RT4803_VOUT_NUM;
+	desc->vsel_mask = RT4803_VSEL_MASK;
+	desc->of_map_mode = rt4803_of_map_mode;
+	if (vsel_act_high)
+		desc->vsel_reg = RT4803_REG_VSELH;
+	else
+		desc->vsel_reg = RT4803_REG_VSELL;
+
+	cfg.dev = dev;
+	cfg.of_node = dev_of_node(dev);
+	cfg.init_data = of_get_regulator_init_data(dev, dev_of_node(dev), desc);
+
+	rdev = devm_regulator_register(dev, desc, &cfg);
+	return PTR_ERR_OR_ZERO(rdev);
+}
+
+static const struct of_device_id rt4803_device_match_table[] = {
+	{ .compatible = "richtek,rt4803" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, rt4803_device_match_table);
+
+static struct i2c_driver rt4803_driver = {
+	.driver = {
+		.name = "rt4803",
+		.of_match_table = rt4803_device_match_table,
+	},
+	.probe = rt4803_probe,
+};
+module_i2c_driver(rt4803_driver);
+
+MODULE_DESCRIPTION("Richtek RT4803 voltage regulator driver");
+MODULE_AUTHOR("ChiYuan Huang <cy_huang@richtek.com>");
+MODULE_LICENSE("GPL");