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, 154 insertions, 0 deletions

diff --git a/drivers/mfd/88pm886.c b/drivers/mfd/88pm886.c
new file mode 100644
index 000000000..e411d8dee
--- /dev/null
+++ b/drivers/mfd/88pm886.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/i2c.h>
+#include <linux/mfd/core.h>
+#include <linux/module.h>
+#include <linux/notifier.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reboot.h>
+#include <linux/regmap.h>
+
+#include <linux/mfd/88pm886.h>
+
+static const struct regmap_config pm886_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = PM886_REG_RTC_SPARE6,
+};
+
+static const struct regmap_irq pm886_regmap_irqs[] = {
+	REGMAP_IRQ_REG(PM886_IRQ_ONKEY, 0, PM886_INT_ENA1_ONKEY),
+};
+
+static const struct regmap_irq_chip pm886_regmap_irq_chip = {
+	.name = "88pm886",
+	.irqs = pm886_regmap_irqs,
+	.num_irqs = ARRAY_SIZE(pm886_regmap_irqs),
+	.num_regs = 4,
+	.status_base = PM886_REG_INT_STATUS1,
+	.ack_base = PM886_REG_INT_STATUS1,
+	.unmask_base = PM886_REG_INT_ENA_1,
+};
+
+static const struct resource pm886_onkey_resources[] = {
+	DEFINE_RES_IRQ_NAMED(PM886_IRQ_ONKEY, "88pm886-onkey"),
+};
+
+static const struct mfd_cell pm886_devs[] = {
+	MFD_CELL_NAME("88pm886-gpadc"),
+	MFD_CELL_RES("88pm886-onkey", pm886_onkey_resources),
+	MFD_CELL_NAME("88pm886-regulator"),
+	MFD_CELL_NAME("88pm886-rtc"),
+};
+
+static int pm886_power_off_handler(struct sys_off_data *sys_off_data)
+{
+	struct pm886_chip *chip = sys_off_data->cb_data;
+	struct regmap *regmap = chip->regmap;
+	struct device *dev = &chip->client->dev;
+	int err;
+
+	err = regmap_update_bits(regmap, PM886_REG_MISC_CONFIG1, PM886_SW_PDOWN, PM886_SW_PDOWN);
+	if (err) {
+		dev_err(dev, "Failed to power off the device: %d\n", err);
+		return NOTIFY_BAD;
+	}
+	return NOTIFY_DONE;
+}
+
+static int pm886_setup_irq(struct pm886_chip *chip,
+		struct regmap_irq_chip_data **irq_data)
+{
+	struct regmap *regmap = chip->regmap;
+	struct device *dev = &chip->client->dev;
+	int err;
+
+	/* Set interrupt clearing mode to clear on write. */
+	err = regmap_update_bits(regmap, PM886_REG_MISC_CONFIG2,
+			PM886_INT_INV | PM886_INT_CLEAR | PM886_INT_MASK_MODE,
+			PM886_INT_WC);
+	if (err) {
+		dev_err(dev, "Failed to set interrupt clearing mode: %d\n", err);
+		return err;
+	}
+
+	err = devm_regmap_add_irq_chip(dev, regmap, chip->client->irq,
+					IRQF_ONESHOT, 0, &pm886_regmap_irq_chip,
+					irq_data);
+	if (err) {
+		dev_err(dev, "Failed to request IRQ: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
+static int pm886_probe(struct i2c_client *client)
+{
+	struct regmap_irq_chip_data *irq_data;
+	struct device *dev = &client->dev;
+	struct pm886_chip *chip;
+	struct regmap *regmap;
+	unsigned int chip_id;
+	int err;
+
+	chip = devm_kzalloc(dev, sizeof(*chip), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
+
+	chip->client = client;
+	chip->chip_id = (uintptr_t)device_get_match_data(dev);
+	i2c_set_clientdata(client, chip);
+
+	regmap = devm_regmap_init_i2c(client, &pm886_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap), "Failed to initialize regmap\n");
+	chip->regmap = regmap;
+
+	err = regmap_read(regmap, PM886_REG_ID, &chip_id);
+	if (err)
+		return dev_err_probe(dev, err, "Failed to read chip ID\n");
+
+	if (chip->chip_id != chip_id)
+		return dev_err_probe(dev, -EINVAL, "Unsupported chip: 0x%x\n", chip_id);
+
+	err = pm886_setup_irq(chip, &irq_data);
+	if (err)
+		return err;
+
+	err = devm_mfd_add_devices(dev, PLATFORM_DEVID_NONE, pm886_devs, ARRAY_SIZE(pm886_devs),
+				NULL, 0, regmap_irq_get_domain(irq_data));
+	if (err)
+		return dev_err_probe(dev, err, "Failed to add devices\n");
+
+	err = devm_register_power_off_handler(dev, pm886_power_off_handler, chip);
+	if (err)
+		return dev_err_probe(dev, err, "Failed to register power off handler\n");
+
+	if (device_property_read_bool(dev, "wakeup-source")) {
+		err = devm_device_init_wakeup(dev);
+		if (err)
+			return dev_err_probe(dev, err, "Failed to init wakeup\n");
+	}
+
+	return 0;
+}
+
+static const struct of_device_id pm886_of_match[] = {
+	{ .compatible = "marvell,88pm886-a1", .data = (void *)PM886_A1_CHIP_ID },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, pm886_of_match);
+
+static struct i2c_driver pm886_i2c_driver = {
+	.driver = {
+		.name = "88pm886",
+		.of_match_table = pm886_of_match,
+	},
+	.probe = pm886_probe,
+};
+module_i2c_driver(pm886_i2c_driver);
+
+MODULE_DESCRIPTION("Marvell 88PM886 PMIC driver");
+MODULE_AUTHOR("Karel Balej <balejk@matfyz.cz>");
+MODULE_LICENSE("GPL");