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, 384 insertions, 0 deletions

diff --git a/drivers/regulator/ltc3676.c b/drivers/regulator/ltc3676.c
new file mode 100644
index 000000000..768cdce0d
--- /dev/null
+++ b/drivers/regulator/ltc3676.c
@@ -0,0 +1,384 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2016 Gateworks Corporation, Inc. All Rights Reserved.
+ */
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+#include <linux/regulator/driver.h>
+#include <linux/regulator/machine.h>
+#include <linux/regulator/of_regulator.h>
+
+#define DRIVER_NAME		"ltc3676"
+
+/* LTC3676 Registers */
+#define LTC3676_BUCK1     0x01
+#define LTC3676_BUCK2     0x02
+#define LTC3676_BUCK3     0x03
+#define LTC3676_BUCK4     0x04
+#define LTC3676_LDOA      0x05
+#define LTC3676_LDOB      0x06
+#define LTC3676_SQD1      0x07
+#define LTC3676_SQD2      0x08
+#define LTC3676_CNTRL     0x09
+#define LTC3676_DVB1A     0x0A
+#define LTC3676_DVB1B     0x0B
+#define LTC3676_DVB2A     0x0C
+#define LTC3676_DVB2B     0x0D
+#define LTC3676_DVB3A     0x0E
+#define LTC3676_DVB3B     0x0F
+#define LTC3676_DVB4A     0x10
+#define LTC3676_DVB4B     0x11
+#define LTC3676_MSKIRQ    0x12
+#define LTC3676_MSKPG     0x13
+#define LTC3676_USER      0x14
+#define LTC3676_IRQSTAT   0x15
+#define LTC3676_PGSTATL   0x16
+#define LTC3676_PGSTATRT  0x17
+#define LTC3676_HRST      0x1E
+#define LTC3676_CLIRQ     0x1F
+
+#define LTC3676_DVBxA_REF_SELECT	BIT(5)
+#define LTC3676_DVBxB_PGOOD_MASK	BIT(5)
+
+#define LTC3676_IRQSTAT_PGOOD_TIMEOUT	BIT(2)
+#define LTC3676_IRQSTAT_UNDERVOLT_WARN	BIT(3)
+#define LTC3676_IRQSTAT_UNDERVOLT_FAULT	BIT(4)
+#define LTC3676_IRQSTAT_THERMAL_WARN	BIT(5)
+#define LTC3676_IRQSTAT_THERMAL_FAULT	BIT(6)
+
+enum ltc3676_reg {
+	LTC3676_SW1,
+	LTC3676_SW2,
+	LTC3676_SW3,
+	LTC3676_SW4,
+	LTC3676_LDO1,
+	LTC3676_LDO2,
+	LTC3676_LDO3,
+	LTC3676_LDO4,
+	LTC3676_NUM_REGULATORS,
+};
+
+struct ltc3676 {
+	struct regmap *regmap;
+	struct device *dev;
+	struct regulator_desc regulator_descs[LTC3676_NUM_REGULATORS];
+	struct regulator_dev *regulators[LTC3676_NUM_REGULATORS];
+};
+
+static int ltc3676_set_suspend_voltage(struct regulator_dev *rdev, int uV)
+{
+	struct ltc3676 *ltc3676 = rdev_get_drvdata(rdev);
+	struct device *dev = ltc3676->dev;
+	int dcdc = rdev_get_id(rdev);
+	int sel;
+
+	dev_dbg(dev, "%s id=%d uV=%d\n", __func__, dcdc, uV);
+	sel = regulator_map_voltage_linear(rdev, uV, uV);
+	if (sel < 0)
+		return sel;
+
+	/* DVBB register follows right after the corresponding DVBA register */
+	return regmap_update_bits(ltc3676->regmap, rdev->desc->vsel_reg + 1,
+				  rdev->desc->vsel_mask, sel);
+}
+
+static int ltc3676_set_suspend_mode(struct regulator_dev *rdev,
+				    unsigned int mode)
+{
+	struct ltc3676 *ltc3676= rdev_get_drvdata(rdev);
+	struct device *dev = ltc3676->dev;
+	int mask, val;
+	int dcdc = rdev_get_id(rdev);
+
+	dev_dbg(dev, "%s id=%d mode=%d\n", __func__, dcdc, mode);
+
+	mask = LTC3676_DVBxA_REF_SELECT;
+	switch (mode) {
+	case REGULATOR_MODE_STANDBY:
+		val = 0; /* select DVBxA */
+		break;
+	case REGULATOR_MODE_NORMAL:
+		val = LTC3676_DVBxA_REF_SELECT; /* select DVBxB */
+		break;
+	default:
+		dev_warn(&rdev->dev, "%s: regulator mode: 0x%x not supported\n",
+			 rdev->desc->name, mode);
+		return -EINVAL;
+	}
+
+	return regmap_update_bits(ltc3676->regmap, rdev->desc->vsel_reg,
+				  mask, val);
+}
+
+static int ltc3676_set_voltage_sel(struct regulator_dev *rdev, unsigned selector)
+{
+	struct ltc3676 *ltc3676 = rdev_get_drvdata(rdev);
+	struct device *dev = ltc3676->dev;
+	int ret, dcdc = rdev_get_id(rdev);
+
+	dev_dbg(dev, "%s id=%d selector=%d\n", __func__, dcdc, selector);
+
+	ret = regmap_update_bits(ltc3676->regmap, rdev->desc->vsel_reg + 1,
+				 LTC3676_DVBxB_PGOOD_MASK,
+				 LTC3676_DVBxB_PGOOD_MASK);
+	if (ret)
+		return ret;
+
+	return regulator_set_voltage_sel_regmap(rdev, selector);
+}
+
+static inline unsigned int ltc3676_scale(unsigned int uV, u32 r1, u32 r2)
+{
+	uint64_t tmp;
+	if (uV == 0)
+		return 0;
+	tmp = (uint64_t)uV * r1;
+	do_div(tmp, r2);
+	return uV + (unsigned int)tmp;
+}
+
+static int ltc3676_of_parse_cb(struct device_node *np,
+			       const struct regulator_desc *desc,
+			       struct regulator_config *config)
+{
+	struct ltc3676 *ltc3676 = config->driver_data;
+	struct regulator_desc *rdesc = &ltc3676->regulator_descs[desc->id];
+	u32 r[2];
+	int ret;
+
+	/* LDO3 has a fixed output */
+	if (desc->id == LTC3676_LDO3)
+		return 0;
+
+	ret = of_property_read_u32_array(np, "lltc,fb-voltage-divider", r, 2);
+	if (ret) {
+		dev_err(ltc3676->dev, "Failed to parse voltage divider: %d\n",
+			ret);
+		return ret;
+	}
+
+	rdesc->min_uV = ltc3676_scale(desc->min_uV, r[0], r[1]);
+	rdesc->uV_step = ltc3676_scale(desc->uV_step, r[0], r[1]);
+	rdesc->fixed_uV = ltc3676_scale(desc->fixed_uV, r[0], r[1]);
+
+	return 0;
+}
+
+/* SW1, SW2, SW3, SW4 linear 0.8V-3.3V with scalar via R1/R2 feeback res */
+static const struct regulator_ops ltc3676_linear_regulator_ops = {
+	.enable = regulator_enable_regmap,
+	.disable = regulator_disable_regmap,
+	.is_enabled = regulator_is_enabled_regmap,
+	.list_voltage = regulator_list_voltage_linear,
+	.set_voltage_sel = ltc3676_set_voltage_sel,
+	.get_voltage_sel = regulator_get_voltage_sel_regmap,
+	.set_suspend_voltage = ltc3676_set_suspend_voltage,
+	.set_suspend_mode = ltc3676_set_suspend_mode,
+};
+
+/* LDO1 always on fixed 0.8V-3.3V via scalar via R1/R2 feeback res */
+static const struct regulator_ops ltc3676_fixed_standby_regulator_ops = {
+};
+
+/* LDO2, LDO3 fixed (LDO2 has external scalar via R1/R2 feedback res) */
+static const struct regulator_ops ltc3676_fixed_regulator_ops = {
+	.enable = regulator_enable_regmap,
+	.disable = regulator_disable_regmap,
+	.is_enabled = regulator_is_enabled_regmap,
+};
+
+#define LTC3676_REG(_id, _name, _ops, en_reg, en_bit, dvba_reg, dvb_mask)   \
+	[LTC3676_ ## _id] = {                                        \
+		.name = #_name,                                \
+		.of_match = of_match_ptr(#_name),              \
+		.regulators_node = of_match_ptr("regulators"), \
+		.of_parse_cb = ltc3676_of_parse_cb,            \
+		.n_voltages = (dvb_mask) + 1,                  \
+		.min_uV = (dvba_reg) ? 412500 : 0,             \
+		.uV_step = (dvba_reg) ? 12500 : 0,             \
+		.ramp_delay = (dvba_reg) ? 800 : 0,            \
+		.fixed_uV = (dvb_mask) ? 0 : 725000,           \
+		.ops = &ltc3676_ ## _ops ## _regulator_ops,    \
+		.type = REGULATOR_VOLTAGE,                     \
+		.id = LTC3676_ ## _id,                         \
+		.owner = THIS_MODULE,                          \
+		.vsel_reg = (dvba_reg),                        \
+		.vsel_mask = (dvb_mask),                       \
+		.enable_reg = (en_reg),                        \
+		.enable_mask = (1 << en_bit),                  \
+	}
+
+#define LTC3676_LINEAR_REG(_id, _name, _en, _dvba)                     \
+	LTC3676_REG(_id, _name, linear,                                \
+		    LTC3676_ ## _en, 7,                                \
+		    LTC3676_ ## _dvba, 0x1f)
+
+#define LTC3676_FIXED_REG(_id, _name, _en_reg, _en_bit)                \
+	LTC3676_REG(_id, _name, fixed, LTC3676_ ## _en_reg, _en_bit, 0, 0)
+
+static const struct regulator_desc ltc3676_regulators[LTC3676_NUM_REGULATORS] = {
+	LTC3676_LINEAR_REG(SW1, sw1, BUCK1, DVB1A),
+	LTC3676_LINEAR_REG(SW2, sw2, BUCK2, DVB2A),
+	LTC3676_LINEAR_REG(SW3, sw3, BUCK3, DVB3A),
+	LTC3676_LINEAR_REG(SW4, sw4, BUCK4, DVB4A),
+	LTC3676_REG(LDO1, ldo1, fixed_standby, 0, 0, 0, 0),
+	LTC3676_FIXED_REG(LDO2, ldo2, LDOA, 2),
+	LTC3676_FIXED_REG(LDO3, ldo3, LDOA, 5),
+	LTC3676_FIXED_REG(LDO4, ldo4, LDOB, 2),
+};
+
+static bool ltc3676_readable_writeable_reg(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case LTC3676_BUCK1 ... LTC3676_IRQSTAT:
+	case LTC3676_HRST:
+	case LTC3676_CLIRQ:
+		return true;
+	}
+	return false;
+}
+
+static bool ltc3676_volatile_reg(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case LTC3676_IRQSTAT ... LTC3676_PGSTATRT:
+		return true;
+	}
+	return false;
+}
+
+static const struct regmap_config ltc3676_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.writeable_reg = ltc3676_readable_writeable_reg,
+	.readable_reg = ltc3676_readable_writeable_reg,
+	.volatile_reg = ltc3676_volatile_reg,
+	.max_register = LTC3676_CLIRQ,
+	.use_single_read = true,
+	.use_single_write = true,
+	.cache_type = REGCACHE_MAPLE,
+};
+
+static irqreturn_t ltc3676_isr(int irq, void *dev_id)
+{
+	struct ltc3676 *ltc3676 = dev_id;
+	struct device *dev = ltc3676->dev;
+	unsigned int i, irqstat, event;
+
+	regmap_read(ltc3676->regmap, LTC3676_IRQSTAT, &irqstat);
+
+	dev_dbg(dev, "irq%d irqstat=0x%02x\n", irq, irqstat);
+	if (irqstat & LTC3676_IRQSTAT_THERMAL_WARN) {
+		dev_warn(dev, "Over-temperature Warning\n");
+		event = REGULATOR_EVENT_OVER_TEMP;
+		for (i = 0; i < LTC3676_NUM_REGULATORS; i++)
+			regulator_notifier_call_chain(ltc3676->regulators[i],
+						      event, NULL);
+	}
+
+	if (irqstat & LTC3676_IRQSTAT_UNDERVOLT_WARN) {
+		dev_info(dev, "Undervoltage Warning\n");
+		event = REGULATOR_EVENT_UNDER_VOLTAGE;
+		for (i = 0; i < LTC3676_NUM_REGULATORS; i++)
+			regulator_notifier_call_chain(ltc3676->regulators[i],
+						      event, NULL);
+	}
+
+	/* Clear warning condition */
+	regmap_write(ltc3676->regmap, LTC3676_CLIRQ, 0);
+
+	return IRQ_HANDLED;
+}
+
+static int ltc3676_regulator_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct regulator_init_data *init_data = dev_get_platdata(dev);
+	struct regulator_desc *descs;
+	struct ltc3676 *ltc3676;
+	int i, ret;
+
+	ltc3676 = devm_kzalloc(dev, sizeof(*ltc3676), GFP_KERNEL);
+	if (!ltc3676)
+		return -ENOMEM;
+
+	i2c_set_clientdata(client, ltc3676);
+	ltc3676->dev = dev;
+
+	descs = ltc3676->regulator_descs;
+	memcpy(descs, ltc3676_regulators, sizeof(ltc3676_regulators));
+	descs[LTC3676_LDO3].fixed_uV = 1800000; /* LDO3 is fixed 1.8V */
+
+	ltc3676->regmap = devm_regmap_init_i2c(client, &ltc3676_regmap_config);
+	if (IS_ERR(ltc3676->regmap)) {
+		ret = PTR_ERR(ltc3676->regmap);
+		dev_err(dev, "failed to initialize regmap: %d\n", ret);
+		return ret;
+	}
+
+	for (i = 0; i < LTC3676_NUM_REGULATORS; i++) {
+		struct regulator_desc *desc = &ltc3676->regulator_descs[i];
+		struct regulator_config config = { };
+
+		if (init_data)
+			config.init_data = &init_data[i];
+
+		config.dev = dev;
+		config.driver_data = ltc3676;
+
+		ltc3676->regulators[i] = devm_regulator_register(dev, desc,
+								 &config);
+		if (IS_ERR(ltc3676->regulators[i])) {
+			ret = PTR_ERR(ltc3676->regulators[i]);
+			dev_err(dev, "failed to register regulator %s: %d\n",
+				desc->name, ret);
+			return ret;
+		}
+	}
+
+	regmap_write(ltc3676->regmap, LTC3676_CLIRQ, 0);
+	if (client->irq) {
+		ret = devm_request_threaded_irq(dev, client->irq, NULL,
+						ltc3676_isr,
+						IRQF_TRIGGER_LOW | IRQF_ONESHOT,
+						client->name, ltc3676);
+		if (ret) {
+			dev_err(dev, "Failed to request IRQ: %d\n", ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static const struct i2c_device_id ltc3676_i2c_id[] = {
+	{ "ltc3676" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ltc3676_i2c_id);
+
+static const struct of_device_id __maybe_unused ltc3676_of_match[] = {
+	{ .compatible = "lltc,ltc3676" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ltc3676_of_match);
+
+static struct i2c_driver ltc3676_driver = {
+	.driver = {
+		.name = DRIVER_NAME,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = of_match_ptr(ltc3676_of_match),
+	},
+	.probe = ltc3676_regulator_probe,
+	.id_table = ltc3676_i2c_id,
+};
+module_i2c_driver(ltc3676_driver);
+
+MODULE_AUTHOR("Tim Harvey <tharvey@gateworks.com>");
+MODULE_DESCRIPTION("Regulator driver for Linear Technology LTC3676");
+MODULE_LICENSE("GPL v2");