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, 299 insertions, 0 deletions

diff --git a/drivers/mfd/rc5t583.c b/drivers/mfd/rc5t583.c
new file mode 100644
index 000000000..2c0e8e963
--- /dev/null
+++ b/drivers/mfd/rc5t583.c
@@ -0,0 +1,299 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Core driver access RC5T583 power management chip.
+ *
+ * Copyright (c) 2011-2012, NVIDIA CORPORATION.  All rights reserved.
+ * Author: Laxman dewangan <ldewangan@nvidia.com>
+ *
+ * Based on code
+ *	Copyright (C) 2011 RICOH COMPANY,LTD
+ */
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/i2c.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/rc5t583.h>
+#include <linux/regmap.h>
+
+#define RICOH_ONOFFSEL_REG	0x10
+#define RICOH_SWCTL_REG		0x5E
+
+struct deepsleep_control_data {
+	u8 reg_add;
+	u8 ds_pos_bit;
+};
+
+#define DEEPSLEEP_INIT(_id, _reg, _pos)		\
+	{					\
+		.reg_add = RC5T583_##_reg,	\
+		.ds_pos_bit = _pos,		\
+	}
+
+static struct deepsleep_control_data deepsleep_data[] = {
+	DEEPSLEEP_INIT(DC0, SLPSEQ1, 0),
+	DEEPSLEEP_INIT(DC1, SLPSEQ1, 4),
+	DEEPSLEEP_INIT(DC2, SLPSEQ2, 0),
+	DEEPSLEEP_INIT(DC3, SLPSEQ2, 4),
+	DEEPSLEEP_INIT(LDO0, SLPSEQ3, 0),
+	DEEPSLEEP_INIT(LDO1, SLPSEQ3, 4),
+	DEEPSLEEP_INIT(LDO2, SLPSEQ4, 0),
+	DEEPSLEEP_INIT(LDO3, SLPSEQ4, 4),
+	DEEPSLEEP_INIT(LDO4, SLPSEQ5, 0),
+	DEEPSLEEP_INIT(LDO5, SLPSEQ5, 4),
+	DEEPSLEEP_INIT(LDO6, SLPSEQ6, 0),
+	DEEPSLEEP_INIT(LDO7, SLPSEQ6, 4),
+	DEEPSLEEP_INIT(LDO8, SLPSEQ7, 0),
+	DEEPSLEEP_INIT(LDO9, SLPSEQ7, 4),
+	DEEPSLEEP_INIT(PSO0, SLPSEQ8, 0),
+	DEEPSLEEP_INIT(PSO1, SLPSEQ8, 4),
+	DEEPSLEEP_INIT(PSO2, SLPSEQ9, 0),
+	DEEPSLEEP_INIT(PSO3, SLPSEQ9, 4),
+	DEEPSLEEP_INIT(PSO4, SLPSEQ10, 0),
+	DEEPSLEEP_INIT(PSO5, SLPSEQ10, 4),
+	DEEPSLEEP_INIT(PSO6, SLPSEQ11, 0),
+	DEEPSLEEP_INIT(PSO7, SLPSEQ11, 4),
+};
+
+#define EXT_PWR_REQ		\
+	(RC5T583_EXT_PWRREQ1_CONTROL | RC5T583_EXT_PWRREQ2_CONTROL)
+
+static const struct mfd_cell rc5t583_subdevs[] = {
+	{.name = "rc5t583-gpio",},
+	{.name = "rc5t583-regulator",},
+	{.name = "rc5t583-rtc",      },
+	{.name = "rc5t583-key",      }
+};
+
+static int __rc5t583_set_ext_pwrreq1_control(struct device *dev,
+	int id, int ext_pwr, int slots)
+{
+	int ret;
+	uint8_t sleepseq_val = 0;
+	unsigned int en_bit;
+	unsigned int slot_bit;
+
+	if (id == RC5T583_DS_DC0) {
+		dev_err(dev, "PWRREQ1 is invalid control for rail %d\n", id);
+		return -EINVAL;
+	}
+
+	en_bit = deepsleep_data[id].ds_pos_bit;
+	slot_bit = en_bit + 1;
+	ret = rc5t583_read(dev, deepsleep_data[id].reg_add, &sleepseq_val);
+	if (ret < 0) {
+		dev_err(dev, "Error in reading reg 0x%x\n",
+				deepsleep_data[id].reg_add);
+		return ret;
+	}
+
+	sleepseq_val &= ~(0xF << en_bit);
+	sleepseq_val |= BIT(en_bit);
+	sleepseq_val |= ((slots & 0x7) << slot_bit);
+	ret = rc5t583_set_bits(dev, RICOH_ONOFFSEL_REG, BIT(1));
+	if (ret < 0) {
+		dev_err(dev, "Error in updating the 0x%02x register\n",
+				RICOH_ONOFFSEL_REG);
+		return ret;
+	}
+
+	ret = rc5t583_write(dev, deepsleep_data[id].reg_add, sleepseq_val);
+	if (ret < 0) {
+		dev_err(dev, "Error in writing reg 0x%x\n",
+				deepsleep_data[id].reg_add);
+		return ret;
+	}
+
+	if (id == RC5T583_DS_LDO4) {
+		ret = rc5t583_write(dev, RICOH_SWCTL_REG, 0x1);
+		if (ret < 0)
+			dev_err(dev, "Error in writing reg 0x%x\n",
+				RICOH_SWCTL_REG);
+	}
+	return ret;
+}
+
+static int __rc5t583_set_ext_pwrreq2_control(struct device *dev,
+	int id, int ext_pwr)
+{
+	int ret;
+
+	if (id != RC5T583_DS_DC0) {
+		dev_err(dev, "PWRREQ2 is invalid control for rail %d\n", id);
+		return -EINVAL;
+	}
+
+	ret = rc5t583_set_bits(dev, RICOH_ONOFFSEL_REG, BIT(2));
+	if (ret < 0)
+		dev_err(dev, "Error in updating the ONOFFSEL 0x10 register\n");
+	return ret;
+}
+
+int rc5t583_ext_power_req_config(struct device *dev, int ds_id,
+	int ext_pwr_req, int deepsleep_slot_nr)
+{
+	if ((ext_pwr_req & EXT_PWR_REQ) == EXT_PWR_REQ)
+		return -EINVAL;
+
+	if (ext_pwr_req & RC5T583_EXT_PWRREQ1_CONTROL)
+		return __rc5t583_set_ext_pwrreq1_control(dev, ds_id,
+				ext_pwr_req, deepsleep_slot_nr);
+
+	if (ext_pwr_req & RC5T583_EXT_PWRREQ2_CONTROL)
+		return __rc5t583_set_ext_pwrreq2_control(dev,
+			ds_id, ext_pwr_req);
+	return 0;
+}
+EXPORT_SYMBOL(rc5t583_ext_power_req_config);
+
+static int rc5t583_clear_ext_power_req(struct rc5t583 *rc5t583,
+	struct rc5t583_platform_data *pdata)
+{
+	int ret;
+	int i;
+	uint8_t on_off_val = 0;
+
+	/*  Clear ONOFFSEL register */
+	if (pdata->enable_shutdown)
+		on_off_val = 0x1;
+
+	ret = rc5t583_write(rc5t583->dev, RICOH_ONOFFSEL_REG, on_off_val);
+	if (ret < 0)
+		dev_warn(rc5t583->dev, "Error in writing reg %d error: %d\n",
+					RICOH_ONOFFSEL_REG, ret);
+
+	ret = rc5t583_write(rc5t583->dev, RICOH_SWCTL_REG, 0x0);
+	if (ret < 0)
+		dev_warn(rc5t583->dev, "Error in writing reg %d error: %d\n",
+					RICOH_SWCTL_REG, ret);
+
+	/* Clear sleep sequence register */
+	for (i = RC5T583_SLPSEQ1; i <= RC5T583_SLPSEQ11; ++i) {
+		ret = rc5t583_write(rc5t583->dev, i, 0x0);
+		if (ret < 0)
+			dev_warn(rc5t583->dev,
+				"Error in writing reg 0x%02x error: %d\n",
+				i, ret);
+	}
+	return 0;
+}
+
+static bool volatile_reg(struct device *dev, unsigned int reg)
+{
+	/* Enable caching in interrupt registers */
+	switch (reg) {
+	case RC5T583_INT_EN_SYS1:
+	case RC5T583_INT_EN_SYS2:
+	case RC5T583_INT_EN_DCDC:
+	case RC5T583_INT_EN_RTC:
+	case RC5T583_INT_EN_ADC1:
+	case RC5T583_INT_EN_ADC2:
+	case RC5T583_INT_EN_ADC3:
+	case RC5T583_GPIO_GPEDGE1:
+	case RC5T583_GPIO_GPEDGE2:
+	case RC5T583_GPIO_EN_INT:
+		return false;
+
+	case RC5T583_GPIO_MON_IOIN:
+		/* This is gpio input register */
+		return true;
+
+	default:
+		/* Enable caching in gpio registers */
+		if ((reg >= RC5T583_GPIO_IOSEL) &&
+				(reg <= RC5T583_GPIO_GPOFUNC))
+			return false;
+
+		/* Enable caching in sleep seq registers */
+		if ((reg >= RC5T583_SLPSEQ1) && (reg <= RC5T583_SLPSEQ11))
+			return false;
+
+		/* Enable caching of regulator registers */
+		if ((reg >= RC5T583_REG_DC0CTL) && (reg <= RC5T583_REG_SR3CTL))
+			return false;
+		if ((reg >= RC5T583_REG_LDOEN1) &&
+					(reg <= RC5T583_REG_LDO9DAC_DS))
+			return false;
+
+		break;
+	}
+
+	return true;
+}
+
+static const struct regmap_config rc5t583_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.volatile_reg = volatile_reg,
+	.max_register = RC5T583_MAX_REG,
+	.num_reg_defaults_raw = RC5T583_NUM_REGS,
+	.cache_type = REGCACHE_MAPLE,
+};
+
+static int rc5t583_i2c_probe(struct i2c_client *i2c)
+{
+	struct rc5t583 *rc5t583;
+	struct rc5t583_platform_data *pdata = dev_get_platdata(&i2c->dev);
+	int ret;
+
+	if (!pdata) {
+		dev_err(&i2c->dev, "Err: Platform data not found\n");
+		return -EINVAL;
+	}
+
+	rc5t583 = devm_kzalloc(&i2c->dev, sizeof(*rc5t583), GFP_KERNEL);
+	if (!rc5t583)
+		return -ENOMEM;
+
+	rc5t583->dev = &i2c->dev;
+	i2c_set_clientdata(i2c, rc5t583);
+
+	rc5t583->regmap = devm_regmap_init_i2c(i2c, &rc5t583_regmap_config);
+	if (IS_ERR(rc5t583->regmap)) {
+		ret = PTR_ERR(rc5t583->regmap);
+		dev_err(&i2c->dev, "regmap initialization failed: %d\n", ret);
+		return ret;
+	}
+
+	ret = rc5t583_clear_ext_power_req(rc5t583, pdata);
+	if (ret < 0)
+		return ret;
+
+	if (i2c->irq) {
+		ret = rc5t583_irq_init(rc5t583, i2c->irq, pdata->irq_base);
+		/* Still continue with warning, if irq init fails */
+		if (ret)
+			dev_warn(&i2c->dev, "IRQ init failed: %d\n", ret);
+	}
+
+	ret = devm_mfd_add_devices(rc5t583->dev, -1, rc5t583_subdevs,
+				   ARRAY_SIZE(rc5t583_subdevs), NULL, 0, NULL);
+	if (ret) {
+		dev_err(&i2c->dev, "add mfd devices failed: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct i2c_device_id rc5t583_i2c_id[] = {
+	{.name = "rc5t583", .driver_data = 0},
+	{}
+};
+
+static struct i2c_driver rc5t583_i2c_driver = {
+	.driver = {
+		   .name = "rc5t583",
+		   },
+	.probe = rc5t583_i2c_probe,
+	.id_table = rc5t583_i2c_id,
+};
+
+static int __init rc5t583_i2c_init(void)
+{
+	return i2c_add_driver(&rc5t583_i2c_driver);
+}
+subsys_initcall(rc5t583_i2c_init);