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, 231 insertions, 0 deletions

diff --git a/drivers/mfd/max77650.c b/drivers/mfd/max77650.c
new file mode 100644
index 000000000..75b5dc44e
--- /dev/null
+++ b/drivers/mfd/max77650.c
@@ -0,0 +1,231 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (C) 2018 BayLibre SAS
+// Author: Bartosz Golaszewski <bgolaszewski@baylibre.com>
+//
+// Core MFD driver for MAXIM 77650/77651 charger/power-supply.
+// Programming manual: https://pdfserv.maximintegrated.com/en/an/AN6428.pdf
+
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/max77650.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+
+#define MAX77650_INT_GPI_F_MSK		BIT(0)
+#define MAX77650_INT_GPI_R_MSK		BIT(1)
+#define MAX77650_INT_GPI_MSK \
+			(MAX77650_INT_GPI_F_MSK | MAX77650_INT_GPI_R_MSK)
+#define MAX77650_INT_nEN_F_MSK		BIT(2)
+#define MAX77650_INT_nEN_R_MSK		BIT(3)
+#define MAX77650_INT_TJAL1_R_MSK	BIT(4)
+#define MAX77650_INT_TJAL2_R_MSK	BIT(5)
+#define MAX77650_INT_DOD_R_MSK		BIT(6)
+
+#define MAX77650_INT_THM_MSK		BIT(0)
+#define MAX77650_INT_CHG_MSK		BIT(1)
+#define MAX77650_INT_CHGIN_MSK		BIT(2)
+#define MAX77650_INT_TJ_REG_MSK		BIT(3)
+#define MAX77650_INT_CHGIN_CTRL_MSK	BIT(4)
+#define MAX77650_INT_SYS_CTRL_MSK	BIT(5)
+#define MAX77650_INT_SYS_CNFG_MSK	BIT(6)
+
+#define MAX77650_INT_GLBL_OFFSET	0
+#define MAX77650_INT_CHG_OFFSET		1
+
+#define MAX77650_SBIA_LPM_MASK		BIT(5)
+#define MAX77650_SBIA_LPM_DISABLED	0x00
+
+enum {
+	MAX77650_INT_GPI,
+	MAX77650_INT_nEN_F,
+	MAX77650_INT_nEN_R,
+	MAX77650_INT_TJAL1_R,
+	MAX77650_INT_TJAL2_R,
+	MAX77650_INT_DOD_R,
+	MAX77650_INT_THM,
+	MAX77650_INT_CHG,
+	MAX77650_INT_CHGIN,
+	MAX77650_INT_TJ_REG,
+	MAX77650_INT_CHGIN_CTRL,
+	MAX77650_INT_SYS_CTRL,
+	MAX77650_INT_SYS_CNFG,
+};
+
+static const struct resource max77650_charger_resources[] = {
+	DEFINE_RES_IRQ_NAMED(MAX77650_INT_CHG, "CHG"),
+	DEFINE_RES_IRQ_NAMED(MAX77650_INT_CHGIN, "CHGIN"),
+};
+
+static const struct resource max77650_gpio_resources[] = {
+	DEFINE_RES_IRQ_NAMED(MAX77650_INT_GPI, "GPI"),
+};
+
+static const struct resource max77650_onkey_resources[] = {
+	DEFINE_RES_IRQ_NAMED(MAX77650_INT_nEN_F, "nEN_F"),
+	DEFINE_RES_IRQ_NAMED(MAX77650_INT_nEN_R, "nEN_R"),
+};
+
+static const struct mfd_cell max77650_cells[] = {
+	{
+		.name		= "max77650-regulator",
+		.of_compatible	= "maxim,max77650-regulator",
+	}, {
+		.name		= "max77650-charger",
+		.of_compatible	= "maxim,max77650-charger",
+		.resources	= max77650_charger_resources,
+		.num_resources	= ARRAY_SIZE(max77650_charger_resources),
+	}, {
+		.name		= "max77650-gpio",
+		.of_compatible	= "maxim,max77650-gpio",
+		.resources	= max77650_gpio_resources,
+		.num_resources	= ARRAY_SIZE(max77650_gpio_resources),
+	}, {
+		.name		= "max77650-led",
+		.of_compatible	= "maxim,max77650-led",
+	}, {
+		.name		= "max77650-onkey",
+		.of_compatible	= "maxim,max77650-onkey",
+		.resources	= max77650_onkey_resources,
+		.num_resources	= ARRAY_SIZE(max77650_onkey_resources),
+	},
+};
+
+static const struct regmap_irq max77650_irqs[] = {
+	[MAX77650_INT_GPI] = {
+		.reg_offset = MAX77650_INT_GLBL_OFFSET,
+		.mask = MAX77650_INT_GPI_MSK,
+		.type = {
+			.type_falling_val = MAX77650_INT_GPI_F_MSK,
+			.type_rising_val = MAX77650_INT_GPI_R_MSK,
+			.types_supported = IRQ_TYPE_EDGE_BOTH,
+		},
+	},
+	REGMAP_IRQ_REG(MAX77650_INT_nEN_F,
+		       MAX77650_INT_GLBL_OFFSET, MAX77650_INT_nEN_F_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_nEN_R,
+		       MAX77650_INT_GLBL_OFFSET, MAX77650_INT_nEN_R_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_TJAL1_R,
+		       MAX77650_INT_GLBL_OFFSET, MAX77650_INT_TJAL1_R_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_TJAL2_R,
+		       MAX77650_INT_GLBL_OFFSET, MAX77650_INT_TJAL2_R_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_DOD_R,
+		       MAX77650_INT_GLBL_OFFSET, MAX77650_INT_DOD_R_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_THM,
+		       MAX77650_INT_CHG_OFFSET, MAX77650_INT_THM_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_CHG,
+		       MAX77650_INT_CHG_OFFSET, MAX77650_INT_CHG_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_CHGIN,
+		       MAX77650_INT_CHG_OFFSET, MAX77650_INT_CHGIN_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_TJ_REG,
+		       MAX77650_INT_CHG_OFFSET, MAX77650_INT_TJ_REG_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_CHGIN_CTRL,
+		       MAX77650_INT_CHG_OFFSET, MAX77650_INT_CHGIN_CTRL_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_SYS_CTRL,
+		       MAX77650_INT_CHG_OFFSET, MAX77650_INT_SYS_CTRL_MSK),
+	REGMAP_IRQ_REG(MAX77650_INT_SYS_CNFG,
+		       MAX77650_INT_CHG_OFFSET, MAX77650_INT_SYS_CNFG_MSK),
+};
+
+static const struct regmap_irq_chip max77650_irq_chip = {
+	.name			= "max77650-irq",
+	.irqs			= max77650_irqs,
+	.num_irqs		= ARRAY_SIZE(max77650_irqs),
+	.num_regs		= 2,
+	.status_base		= MAX77650_REG_INT_GLBL,
+	.mask_base		= MAX77650_REG_INTM_GLBL,
+	.type_in_mask		= true,
+	.init_ack_masked	= true,
+	.clear_on_unmask	= true,
+};
+
+static const struct regmap_config max77650_regmap_config = {
+	.name		= "max77650",
+	.reg_bits	= 8,
+	.val_bits	= 8,
+};
+
+static int max77650_i2c_probe(struct i2c_client *i2c)
+{
+	struct regmap_irq_chip_data *irq_data;
+	struct device *dev = &i2c->dev;
+	struct irq_domain *domain;
+	struct regmap *map;
+	unsigned int val;
+	int rv, id;
+
+	map = devm_regmap_init_i2c(i2c, &max77650_regmap_config);
+	if (IS_ERR(map)) {
+		dev_err(dev, "Unable to initialise I2C Regmap\n");
+		return PTR_ERR(map);
+	}
+
+	rv = regmap_read(map, MAX77650_REG_CID, &val);
+	if (rv) {
+		dev_err(dev, "Unable to read Chip ID\n");
+		return rv;
+	}
+
+	id = MAX77650_CID_BITS(val);
+	switch (id) {
+	case MAX77650_CID_77650A:
+	case MAX77650_CID_77650C:
+	case MAX77650_CID_77651A:
+	case MAX77650_CID_77651B:
+		break;
+	default:
+		dev_err(dev, "Chip not supported - ID: 0x%02x\n", id);
+		return -ENODEV;
+	}
+
+	/*
+	 * This IC has a low-power mode which reduces the quiescent current
+	 * consumption to ~5.6uA but is only suitable for systems consuming
+	 * less than ~2mA. Since this is not likely the case even on
+	 * linux-based wearables - keep the chip in normal power mode.
+	 */
+	rv = regmap_update_bits(map,
+				MAX77650_REG_CNFG_GLBL,
+				MAX77650_SBIA_LPM_MASK,
+				MAX77650_SBIA_LPM_DISABLED);
+	if (rv) {
+		dev_err(dev, "Unable to change the power mode\n");
+		return rv;
+	}
+
+	rv = devm_regmap_add_irq_chip(dev, map, i2c->irq,
+				      IRQF_ONESHOT | IRQF_SHARED, 0,
+				      &max77650_irq_chip, &irq_data);
+	if (rv) {
+		dev_err(dev, "Unable to add Regmap IRQ chip\n");
+		return rv;
+	}
+
+	domain = regmap_irq_get_domain(irq_data);
+
+	return devm_mfd_add_devices(dev, PLATFORM_DEVID_NONE,
+				    max77650_cells, ARRAY_SIZE(max77650_cells),
+				    NULL, 0, domain);
+}
+
+static const struct of_device_id max77650_of_match[] = {
+	{ .compatible = "maxim,max77650" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max77650_of_match);
+
+static struct i2c_driver max77650_i2c_driver = {
+	.driver = {
+		.name = "max77650",
+		.of_match_table = max77650_of_match,
+	},
+	.probe = max77650_i2c_probe,
+};
+module_i2c_driver(max77650_i2c_driver);
+
+MODULE_DESCRIPTION("MAXIM 77650/77651 multi-function core driver");
+MODULE_AUTHOR("Bartosz Golaszewski <bgolaszewski@baylibre.com>");
+MODULE_LICENSE("GPL v2");