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, 309 insertions, 0 deletions

diff --git a/drivers/regulator/max1586.c b/drivers/regulator/max1586.c
new file mode 100644
index 000000000..4242fbb7b
--- /dev/null
+++ b/drivers/regulator/max1586.c
@@ -0,0 +1,309 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * max1586.c  --  Voltage and current regulation for the Maxim 1586
+ *
+ * Copyright (C) 2008 Robert Jarzmik
+ */
+#include <linux/module.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/driver.h>
+#include <linux/slab.h>
+#include <linux/regulator/max1586.h>
+#include <linux/of.h>
+#include <linux/regulator/of_regulator.h>
+
+#define MAX1586_V3_MAX_VSEL 31
+#define MAX1586_V6_MAX_VSEL 3
+
+#define MAX1586_V3_MIN_UV   700000
+#define MAX1586_V3_MAX_UV  1475000
+
+#define MAX1586_V6_MIN_UV        0
+#define MAX1586_V6_MAX_UV  3000000
+
+#define I2C_V3_SELECT (0 << 5)
+#define I2C_V6_SELECT (1 << 5)
+
+struct max1586_data {
+	struct i2c_client *client;
+
+	/* min/max V3 voltage */
+	unsigned int min_uV;
+	unsigned int max_uV;
+
+	unsigned int v3_curr_sel;
+	unsigned int v6_curr_sel;
+};
+
+/*
+ * V6 voltage
+ * On I2C bus, sending a "x" byte to the max1586 means :
+ *   set V6 to either 0V, 1.8V, 2.5V, 3V depending on (x & 0x3)
+ * As regulator framework doesn't accept voltages to be 0V, we use 1uV.
+ */
+static const unsigned int v6_voltages_uv[] = { 1, 1800000, 2500000, 3000000 };
+
+/*
+ * V3 voltage
+ * On I2C bus, sending a "x" byte to the max1586 means :
+ *   set V3 to 0.700V + (x & 0x1f) * 0.025V
+ * This voltage can be increased by external resistors
+ * R24 and R25=100kOhm as described in the data sheet.
+ * The gain is approximately: 1 + R24/R25 + R24/185.5kOhm
+ */
+static int max1586_v3_get_voltage_sel(struct regulator_dev *rdev)
+{
+	struct max1586_data *max1586 = rdev_get_drvdata(rdev);
+
+	return max1586->v3_curr_sel;
+}
+
+static int max1586_v3_set_voltage_sel(struct regulator_dev *rdev,
+				      unsigned selector)
+{
+	struct max1586_data *max1586 = rdev_get_drvdata(rdev);
+	struct i2c_client *client = max1586->client;
+	int ret;
+	u8 v3_prog;
+
+	dev_dbg(&client->dev, "changing voltage v3 to %dmv\n",
+		regulator_list_voltage_linear(rdev, selector) / 1000);
+
+	v3_prog = I2C_V3_SELECT | (u8) selector;
+	ret = i2c_smbus_write_byte(client, v3_prog);
+	if (ret)
+		return ret;
+
+	max1586->v3_curr_sel = selector;
+
+	return 0;
+}
+
+static int max1586_v6_get_voltage_sel(struct regulator_dev *rdev)
+{
+	struct max1586_data *max1586 = rdev_get_drvdata(rdev);
+
+	return max1586->v6_curr_sel;
+}
+
+static int max1586_v6_set_voltage_sel(struct regulator_dev *rdev,
+				      unsigned int selector)
+{
+	struct max1586_data *max1586 = rdev_get_drvdata(rdev);
+	struct i2c_client *client = max1586->client;
+	u8 v6_prog;
+	int ret;
+
+	dev_dbg(&client->dev, "changing voltage v6 to %dmv\n",
+		rdev->desc->volt_table[selector] / 1000);
+
+	v6_prog = I2C_V6_SELECT | (u8) selector;
+	ret = i2c_smbus_write_byte(client, v6_prog);
+	if (ret)
+		return ret;
+
+	max1586->v6_curr_sel = selector;
+
+	return 0;
+}
+
+/*
+ * The Maxim 1586 controls V3 and V6 voltages, but offers no way of reading back
+ * the set up value.
+ */
+static const struct regulator_ops max1586_v3_ops = {
+	.get_voltage_sel = max1586_v3_get_voltage_sel,
+	.set_voltage_sel = max1586_v3_set_voltage_sel,
+	.list_voltage = regulator_list_voltage_linear,
+	.map_voltage = regulator_map_voltage_linear,
+};
+
+static const struct regulator_ops max1586_v6_ops = {
+	.get_voltage_sel = max1586_v6_get_voltage_sel,
+	.set_voltage_sel = max1586_v6_set_voltage_sel,
+	.list_voltage = regulator_list_voltage_table,
+};
+
+static struct regulator_desc max1586_reg[] = {
+	{
+		.name = "Output_V3",
+		.id = MAX1586_V3,
+		.ops = &max1586_v3_ops,
+		.type = REGULATOR_VOLTAGE,
+		.n_voltages = MAX1586_V3_MAX_VSEL + 1,
+		.owner = THIS_MODULE,
+	},
+	{
+		.name = "Output_V6",
+		.id = MAX1586_V6,
+		.ops = &max1586_v6_ops,
+		.type = REGULATOR_VOLTAGE,
+		.n_voltages = MAX1586_V6_MAX_VSEL + 1,
+		.volt_table = v6_voltages_uv,
+		.owner = THIS_MODULE,
+	},
+};
+
+static int of_get_max1586_platform_data(struct device *dev,
+				 struct max1586_platform_data *pdata)
+{
+	struct max1586_subdev_data *sub;
+	struct of_regulator_match rmatch[ARRAY_SIZE(max1586_reg)] = { };
+	struct device_node *np = dev->of_node;
+	int i, matched;
+
+	if (of_property_read_u32(np, "v3-gain",
+				 &pdata->v3_gain) < 0) {
+		dev_err(dev, "%pOF has no 'v3-gain' property\n", np);
+		return -EINVAL;
+	}
+
+	np = of_get_child_by_name(np, "regulators");
+	if (!np) {
+		dev_err(dev, "missing 'regulators' subnode in DT\n");
+		return -EINVAL;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(rmatch); i++)
+		rmatch[i].name = max1586_reg[i].name;
+
+	matched = of_regulator_match(dev, np, rmatch, ARRAY_SIZE(rmatch));
+	of_node_put(np);
+	/*
+	 * If matched is 0, ie. neither Output_V3 nor Output_V6 have been found,
+	 * return 0, which signals the normal situation where no subregulator is
+	 * available. This is normal because the max1586 doesn't provide any
+	 * readback support, so the subregulators can't report any status
+	 * anyway.  If matched < 0, return the error.
+	 */
+	if (matched <= 0)
+		return matched;
+
+	pdata->subdevs = devm_kcalloc(dev,
+				      matched,
+				      sizeof(struct max1586_subdev_data),
+				      GFP_KERNEL);
+	if (!pdata->subdevs)
+		return -ENOMEM;
+
+	pdata->num_subdevs = matched;
+	sub = pdata->subdevs;
+
+	for (i = 0; i < matched; i++) {
+		sub->id = i;
+		sub->name = rmatch[i].of_node->name;
+		sub->platform_data = rmatch[i].init_data;
+		sub++;
+	}
+
+	return 0;
+}
+
+static const struct of_device_id __maybe_unused max1586_of_match[] = {
+	{ .compatible = "maxim,max1586", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, max1586_of_match);
+
+static int max1586_pmic_probe(struct i2c_client *client)
+{
+	struct max1586_platform_data *pdata, pdata_of;
+	struct regulator_config config = { };
+	struct max1586_data *max1586;
+	int i, id, ret;
+
+	pdata = dev_get_platdata(&client->dev);
+	if (client->dev.of_node && !pdata) {
+		ret = of_get_max1586_platform_data(&client->dev, &pdata_of);
+		if (ret < 0)
+			return ret;
+		pdata = &pdata_of;
+	}
+
+	max1586 = devm_kzalloc(&client->dev, sizeof(struct max1586_data),
+			GFP_KERNEL);
+	if (!max1586)
+		return -ENOMEM;
+
+	max1586->client = client;
+
+	if (!pdata->v3_gain)
+		return -EINVAL;
+
+	max1586->min_uV = MAX1586_V3_MIN_UV / 1000 * pdata->v3_gain / 1000;
+	max1586->max_uV = MAX1586_V3_MAX_UV / 1000 * pdata->v3_gain / 1000;
+
+	/* Set curr_sel to default voltage on power-up */
+	max1586->v3_curr_sel = 24; /* 1.3V */
+	max1586->v6_curr_sel = 0;
+
+	for (i = 0; i < pdata->num_subdevs && i <= MAX1586_V6; i++) {
+		struct regulator_dev *rdev;
+
+		id = pdata->subdevs[i].id;
+		if (!pdata->subdevs[i].platform_data)
+			continue;
+		if (id < MAX1586_V3 || id > MAX1586_V6) {
+			dev_err(&client->dev, "invalid regulator id %d\n", id);
+			return -EINVAL;
+		}
+
+		if (id == MAX1586_V3) {
+			max1586_reg[id].min_uV = max1586->min_uV;
+			max1586_reg[id].uV_step =
+					(max1586->max_uV - max1586->min_uV) /
+					MAX1586_V3_MAX_VSEL;
+		}
+
+		config.dev = &client->dev;
+		config.init_data = pdata->subdevs[i].platform_data;
+		config.driver_data = max1586;
+
+		rdev = devm_regulator_register(&client->dev,
+						  &max1586_reg[id], &config);
+		if (IS_ERR(rdev)) {
+			dev_err(&client->dev, "failed to register %s\n",
+				max1586_reg[id].name);
+			return PTR_ERR(rdev);
+		}
+	}
+
+	i2c_set_clientdata(client, max1586);
+	dev_info(&client->dev, "Maxim 1586 regulator driver loaded\n");
+	return 0;
+}
+
+static const struct i2c_device_id max1586_id[] = {
+	{ "max1586" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max1586_id);
+
+static struct i2c_driver max1586_pmic_driver = {
+	.probe = max1586_pmic_probe,
+	.driver		= {
+		.name	= "max1586",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = of_match_ptr(max1586_of_match),
+	},
+	.id_table	= max1586_id,
+};
+
+static int __init max1586_pmic_init(void)
+{
+	return i2c_add_driver(&max1586_pmic_driver);
+}
+subsys_initcall(max1586_pmic_init);
+
+static void __exit max1586_pmic_exit(void)
+{
+	i2c_del_driver(&max1586_pmic_driver);
+}
+module_exit(max1586_pmic_exit);
+
+/* Module information */
+MODULE_DESCRIPTION("MAXIM 1586 voltage regulator driver");
+MODULE_AUTHOR("Robert Jarzmik");
+MODULE_LICENSE("GPL");