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, 180 insertions, 0 deletions

diff --git a/drivers/mfd/max77705.c b/drivers/mfd/max77705.c
new file mode 100644
index 000000000..e98c76d6b
--- /dev/null
+++ b/drivers/mfd/max77705.c
@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Maxim MAX77705 PMIC core driver
+ *
+ * Copyright (C) 2025 Dzmitry Sankouski <dsankouski@gmail.com>
+ **/
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/max77705-private.h>
+#include <linux/mfd/max77693-common.h>
+#include <linux/pm.h>
+#include <linux/power/max17042_battery.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/of.h>
+
+static struct mfd_cell max77705_devs[] = {
+	MFD_CELL_OF("max77705-rgb", NULL, NULL, 0, 0, "maxim,max77705-rgb"),
+	MFD_CELL_OF("max77705-charger", NULL, NULL, 0, 0, "maxim,max77705-charger"),
+	MFD_CELL_OF("max77705-haptic", NULL, NULL, 0, 0, "maxim,max77705-haptic"),
+};
+
+static const struct regmap_range max77705_readable_ranges[] = {
+	regmap_reg_range(MAX77705_PMIC_REG_PMICID1,		MAX77705_PMIC_REG_BSTOUT_MASK),
+	regmap_reg_range(MAX77705_PMIC_REG_INTSRC,		MAX77705_PMIC_REG_RESERVED_29),
+	regmap_reg_range(MAX77705_PMIC_REG_BOOSTCONTROL1,	MAX77705_PMIC_REG_BOOSTCONTROL1),
+	regmap_reg_range(MAX77705_PMIC_REG_MCONFIG,		MAX77705_PMIC_REG_MCONFIG2),
+	regmap_reg_range(MAX77705_PMIC_REG_FORCE_EN_MASK,	MAX77705_PMIC_REG_FORCE_EN_MASK),
+	regmap_reg_range(MAX77705_PMIC_REG_BOOSTCONTROL1,	MAX77705_PMIC_REG_BOOSTCONTROL1),
+	regmap_reg_range(MAX77705_PMIC_REG_BOOSTCONTROL2,	MAX77705_PMIC_REG_BOOSTCONTROL2),
+	regmap_reg_range(MAX77705_PMIC_REG_SW_RESET,		MAX77705_PMIC_REG_USBC_RESET),
+};
+
+static const struct regmap_range max77705_writable_ranges[] = {
+	regmap_reg_range(MAX77705_PMIC_REG_MAINCTRL1,		MAX77705_PMIC_REG_BSTOUT_MASK),
+	regmap_reg_range(MAX77705_PMIC_REG_INTSRC,		MAX77705_PMIC_REG_RESERVED_29),
+	regmap_reg_range(MAX77705_PMIC_REG_BOOSTCONTROL1,	MAX77705_PMIC_REG_BOOSTCONTROL1),
+	regmap_reg_range(MAX77705_PMIC_REG_MCONFIG,		MAX77705_PMIC_REG_MCONFIG2),
+	regmap_reg_range(MAX77705_PMIC_REG_FORCE_EN_MASK,	MAX77705_PMIC_REG_FORCE_EN_MASK),
+	regmap_reg_range(MAX77705_PMIC_REG_BOOSTCONTROL1,	MAX77705_PMIC_REG_BOOSTCONTROL1),
+	regmap_reg_range(MAX77705_PMIC_REG_BOOSTCONTROL2,	MAX77705_PMIC_REG_BOOSTCONTROL2),
+	regmap_reg_range(MAX77705_PMIC_REG_SW_RESET,		MAX77705_PMIC_REG_USBC_RESET),
+};
+
+static const struct regmap_access_table max77705_readable_table = {
+	.yes_ranges = max77705_readable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(max77705_readable_ranges),
+};
+
+static const struct regmap_access_table max77705_writable_table = {
+	.yes_ranges = max77705_writable_ranges,
+	.n_yes_ranges = ARRAY_SIZE(max77705_writable_ranges),
+};
+
+static const struct regmap_config max77705_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.rd_table = &max77705_readable_table,
+	.wr_table = &max77705_writable_table,
+	.max_register = MAX77705_PMIC_REG_USBC_RESET,
+};
+
+static const struct regmap_irq max77705_irqs[] = {
+	{ .mask = MAX77705_SRC_IRQ_CHG, },
+	{ .mask = MAX77705_SRC_IRQ_TOP, },
+	{ .mask = MAX77705_SRC_IRQ_FG, },
+	{ .mask = MAX77705_SRC_IRQ_USBC, },
+};
+
+static const struct regmap_irq_chip max77705_irq_chip = {
+	.name		= "max77705",
+	.status_base	= MAX77705_PMIC_REG_INTSRC,
+	.ack_base	= MAX77705_PMIC_REG_INTSRC,
+	.mask_base	= MAX77705_PMIC_REG_INTSRC_MASK,
+	.num_regs	= 1,
+	.irqs		= max77705_irqs,
+	.num_irqs	= ARRAY_SIZE(max77705_irqs),
+};
+
+static int max77705_i2c_probe(struct i2c_client *i2c)
+{
+	struct device *dev = &i2c->dev;
+	struct max77693_dev *max77705;
+	struct regmap_irq_chip_data *irq_data;
+	struct irq_domain *domain;
+	enum max77705_hw_rev pmic_rev;
+	unsigned int pmic_rev_value;
+	int ret;
+
+	max77705 = devm_kzalloc(dev, sizeof(*max77705), GFP_KERNEL);
+	if (!max77705)
+		return -ENOMEM;
+
+	max77705->i2c = i2c;
+	max77705->type = TYPE_MAX77705;
+	i2c_set_clientdata(i2c, max77705);
+
+	max77705->regmap = devm_regmap_init_i2c(i2c, &max77705_regmap_config);
+	if (IS_ERR(max77705->regmap))
+		return PTR_ERR(max77705->regmap);
+
+	ret = regmap_read(max77705->regmap, MAX77705_PMIC_REG_PMICREV, &pmic_rev_value);
+	if (ret < 0)
+		return -ENODEV;
+
+	pmic_rev = pmic_rev_value & MAX77705_REVISION_MASK;
+	if (pmic_rev != MAX77705_PASS3)
+		return dev_err_probe(dev, -ENODEV, "Rev.0x%x is not tested\n", pmic_rev);
+
+	/* Active Discharge Enable */
+	regmap_update_bits(max77705->regmap, MAX77705_PMIC_REG_MAINCTRL1, 1, 1);
+
+	ret = devm_regmap_add_irq_chip(dev, max77705->regmap,
+					i2c->irq,
+					IRQF_ONESHOT, 0,
+					&max77705_irq_chip,
+					&irq_data);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to add IRQ chip\n");
+
+	domain = regmap_irq_get_domain(irq_data);
+
+	ret = devm_mfd_add_devices(dev, PLATFORM_DEVID_NONE,
+				   max77705_devs, ARRAY_SIZE(max77705_devs),
+				   NULL, 0, domain);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to register child devices\n");
+
+	ret = devm_device_init_wakeup(dev);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to init wakeup\n");
+
+	return 0;
+}
+
+static int max77705_suspend(struct device *dev)
+{
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	disable_irq(i2c->irq);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(i2c->irq);
+
+	return 0;
+}
+
+static int max77705_resume(struct device *dev)
+{
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(i2c->irq);
+
+	enable_irq(i2c->irq);
+
+	return 0;
+}
+static DEFINE_SIMPLE_DEV_PM_OPS(max77705_pm_ops, max77705_suspend, max77705_resume);
+
+static const struct of_device_id max77705_i2c_of_match[] = {
+	{ .compatible = "maxim,max77705" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max77705_i2c_of_match);
+
+static struct i2c_driver max77705_i2c_driver = {
+	.driver = {
+		.name			= "max77705",
+		.of_match_table		= max77705_i2c_of_match,
+		.pm			= pm_sleep_ptr(&max77705_pm_ops),
+	},
+	.probe = max77705_i2c_probe
+};
+module_i2c_driver(max77705_i2c_driver);
+
+MODULE_DESCRIPTION("Maxim MAX77705 PMIC core driver");
+MODULE_AUTHOR("Dzmitry Sankouski <dsankouski@gmail.com>");
+MODULE_LICENSE("GPL");