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, 301 insertions, 0 deletions

diff --git a/drivers/extcon/extcon-max14526.c b/drivers/extcon/extcon-max14526.c
new file mode 100644
index 000000000..bf8997827
--- /dev/null
+++ b/drivers/extcon/extcon-max14526.c
@@ -0,0 +1,301 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/device.h>
+#include <linux/devm-helpers.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/extcon-provider.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/pm.h>
+#include <linux/regmap.h>
+
+/* I2C addresses of MUIC internal registers */
+#define MAX14526_DEVICE_ID	0x00
+#define MAX14526_ID		0x02
+
+/* CONTROL_1 register masks */
+#define MAX14526_CONTROL_1	0x01
+#define   ID_2P2		BIT(6)
+#define   ID_620		BIT(5)
+#define   ID_200		BIT(4)
+#define   VLDO			BIT(3)
+#define   SEMREN		BIT(2)
+#define   ADC_EN		BIT(1)
+#define   CP_EN			BIT(0)
+
+/* CONTROL_2 register masks */
+#define MAX14526_CONTROL_2	0x02
+#define   INTPOL		BIT(7)
+#define   INT_EN		BIT(6)
+#define   MIC_LP		BIT(5)
+#define   CP_AUD		BIT(4)
+#define   CHG_TYPE		BIT(1)
+#define   USB_DET_DIS		BIT(0)
+
+/* SW_CONTROL register masks */
+#define MAX14526_SW_CONTROL	0x03
+#define   SW_DATA		0x00
+#define   SW_UART		0x01
+#define   SW_AUDIO		0x02
+#define   SW_OPEN		0x07
+
+/* INT_STATUS register masks */
+#define MAX14526_INT_STAT	0x04
+#define   CHGDET		BIT(7)
+#define   MR_COMP		BIT(6)
+#define   SENDEND		BIT(5)
+#define   V_VBUS		BIT(4)
+
+/* STATUS register masks */
+#define MAX14526_STATUS		0x05
+#define   CPORT			BIT(7)
+#define   CHPORT		BIT(6)
+#define   C1COMP		BIT(0)
+
+enum max14526_idno_resistance {
+	MAX14526_GND,
+	MAX14526_24KOHM,
+	MAX14526_56KOHM,
+	MAX14526_100KOHM,
+	MAX14526_130KOHM,
+	MAX14526_180KOHM,
+	MAX14526_240KOHM,
+	MAX14526_330KOHM,
+	MAX14526_430KOHM,
+	MAX14526_620KOHM,
+	MAX14526_910KOHM,
+	MAX14526_OPEN
+};
+
+enum max14526_field_idx {
+	VENDOR_ID, CHIP_REV,		/* DEVID */
+	DM, DP,				/* SW_CONTROL */
+	MAX14526_N_REGMAP_FIELDS
+};
+
+static const struct reg_field max14526_reg_field[MAX14526_N_REGMAP_FIELDS] = {
+	[VENDOR_ID] = REG_FIELD(MAX14526_DEVICE_ID,  4, 7),
+	[CHIP_REV]  = REG_FIELD(MAX14526_DEVICE_ID,  0, 3),
+	[DM]        = REG_FIELD(MAX14526_SW_CONTROL, 0, 2),
+	[DP]        = REG_FIELD(MAX14526_SW_CONTROL, 3, 5),
+};
+
+struct max14526_data {
+	struct i2c_client *client;
+	struct extcon_dev *edev;
+
+	struct regmap *regmap;
+	struct regmap_field *rfield[MAX14526_N_REGMAP_FIELDS];
+
+	int last_state;
+	int cable;
+};
+
+enum max14526_muic_modes {
+	MAX14526_OTG     = MAX14526_GND, /* no power */
+	MAX14526_MHL     = MAX14526_56KOHM, /* no power */
+	MAX14526_OTG_Y   = MAX14526_GND | V_VBUS,
+	MAX14526_MHL_CHG = MAX14526_GND | V_VBUS | CHGDET,
+	MAX14526_NONE    = MAX14526_OPEN,
+	MAX14526_USB     = MAX14526_OPEN | V_VBUS,
+	MAX14526_CHG     = MAX14526_OPEN | V_VBUS | CHGDET,
+};
+
+static const unsigned int max14526_extcon_cable[] = {
+	EXTCON_USB,
+	EXTCON_USB_HOST,
+	EXTCON_CHG_USB_FAST,
+	EXTCON_DISP_MHL,
+	EXTCON_NONE,
+};
+
+static int max14526_ap_usb_mode(struct max14526_data *priv)
+{
+	struct device *dev = &priv->client->dev;
+	int ret;
+
+	/* Enable USB Path */
+	ret = regmap_field_write(priv->rfield[DM], SW_DATA);
+	if (ret)
+		return ret;
+
+	ret = regmap_field_write(priv->rfield[DP], SW_DATA);
+	if (ret)
+		return ret;
+
+	/* Enable 200K, Charger Pump and ADC */
+	ret = regmap_write(priv->regmap, MAX14526_CONTROL_1,
+			   ID_200 | ADC_EN | CP_EN);
+	if (ret)
+		return ret;
+
+	dev_dbg(dev, "AP USB mode set\n");
+
+	return 0;
+}
+
+static irqreturn_t max14526_interrupt(int irq, void *dev_id)
+{
+	struct max14526_data *priv = dev_id;
+	struct device *dev = &priv->client->dev;
+	int state, ret;
+
+	/*
+	 * Upon an MUIC IRQ (MUIC_INT_N falls), wait at least 70ms
+	 * before reading INT_STAT and STATUS. After the reads,
+	 * MUIC_INT_N returns to high (but the INT_STAT and STATUS
+	 * contents will be held).
+	 */
+	msleep(100);
+
+	ret = regmap_read(priv->regmap, MAX14526_INT_STAT, &state);
+	if (ret)
+		dev_err(dev, "failed to read MUIC state %d\n", ret);
+
+	if (state == priv->last_state)
+		return IRQ_HANDLED;
+
+	/* Detach previous device */
+	extcon_set_state_sync(priv->edev, priv->cable, false);
+
+	switch (state) {
+	case MAX14526_USB:
+		priv->cable = EXTCON_USB;
+		break;
+
+	case MAX14526_CHG:
+		priv->cable = EXTCON_CHG_USB_FAST;
+		break;
+
+	case MAX14526_OTG:
+	case MAX14526_OTG_Y:
+		priv->cable = EXTCON_USB_HOST;
+		break;
+
+	case MAX14526_MHL:
+	case MAX14526_MHL_CHG:
+		priv->cable = EXTCON_DISP_MHL;
+		break;
+
+	case MAX14526_NONE:
+	default:
+		priv->cable = EXTCON_NONE;
+		break;
+	}
+
+	extcon_set_state_sync(priv->edev, priv->cable, true);
+
+	priv->last_state = state;
+
+	return IRQ_HANDLED;
+}
+
+static const struct regmap_config max14526_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = MAX14526_STATUS,
+};
+
+static int max14526_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct max14526_data *priv;
+	int ret, dev_id, rev, i;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->client = client;
+	i2c_set_clientdata(client, priv);
+
+	priv->regmap = devm_regmap_init_i2c(client, &max14526_regmap_config);
+	if (IS_ERR(priv->regmap))
+		return dev_err_probe(dev, PTR_ERR(priv->regmap), "cannot allocate regmap\n");
+
+	for (i = 0; i < MAX14526_N_REGMAP_FIELDS; i++) {
+		priv->rfield[i] = devm_regmap_field_alloc(dev, priv->regmap,
+							  max14526_reg_field[i]);
+		if (IS_ERR(priv->rfield[i]))
+			return dev_err_probe(dev, PTR_ERR(priv->rfield[i]),
+					     "cannot allocate regmap field\n");
+	}
+
+	/* Detect if MUIC version is supported */
+	ret = regmap_field_read(priv->rfield[VENDOR_ID], &dev_id);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to read MUIC ID\n");
+
+	regmap_field_read(priv->rfield[CHIP_REV], &rev);
+
+	if (dev_id == MAX14526_ID)
+		dev_info(dev, "detected MAX14526 MUIC with id 0x%x, rev 0x%x\n", dev_id, rev);
+	else
+		dev_err_probe(dev, -EINVAL, "MUIC vendor id 0x%X is not recognized\n", dev_id);
+
+	priv->edev = devm_extcon_dev_allocate(dev, max14526_extcon_cable);
+	if (IS_ERR(priv->edev))
+		return dev_err_probe(dev, (IS_ERR(priv->edev)),
+				     "failed to allocate extcon device\n");
+
+	ret = devm_extcon_dev_register(dev, priv->edev);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "failed to register extcon device\n");
+
+	ret = max14526_ap_usb_mode(priv);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "failed to set AP USB mode\n");
+
+	regmap_write_bits(priv->regmap, MAX14526_CONTROL_2, INT_EN, INT_EN);
+	regmap_write_bits(priv->regmap, MAX14526_CONTROL_2, USB_DET_DIS, (u32)~USB_DET_DIS);
+
+	ret = devm_request_threaded_irq(dev, client->irq, NULL, &max14526_interrupt,
+					IRQF_ONESHOT | IRQF_SHARED, client->name, priv);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to register IRQ\n");
+
+	irq_wake_thread(client->irq, priv);
+
+	return 0;
+}
+
+static int max14526_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct max14526_data *priv = i2c_get_clientdata(client);
+
+	irq_wake_thread(client->irq, priv);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(max14526_pm_ops, NULL, max14526_resume);
+
+static const struct of_device_id max14526_match[] = {
+	{ .compatible = "maxim,max14526" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, max14526_match);
+
+static const struct i2c_device_id max14526_id[] = {
+	{ "max14526" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max14526_id);
+
+static struct i2c_driver max14526_driver = {
+	.driver = {
+		.name = "max14526",
+		.of_match_table = max14526_match,
+		.pm = &max14526_pm_ops,
+	},
+	.probe = max14526_probe,
+	.id_table = max14526_id,
+};
+module_i2c_driver(max14526_driver);
+
+MODULE_AUTHOR("Svyatoslav Ryhel <clamor95@gmail.com>");
+MODULE_DESCRIPTION("MAX14526 extcon driver to support MUIC");
+MODULE_LICENSE("GPL");