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, 369 insertions, 0 deletions

diff --git a/drivers/nfc/fdp/i2c.c b/drivers/nfc/fdp/i2c.c
new file mode 100644
index 000000000..c1896a1d9
--- /dev/null
+++ b/drivers/nfc/fdp/i2c.c
@@ -0,0 +1,369 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* -------------------------------------------------------------------------
+ * Copyright (C) 2014-2016, Intel Corporation
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include <linux/module.h>
+#include <linux/acpi.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/nfc.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <net/nfc/nfc.h>
+#include <net/nfc/nci_core.h>
+
+#include "fdp.h"
+
+#define FDP_I2C_DRIVER_NAME	"fdp_nci_i2c"
+
+#define FDP_DP_CLOCK_TYPE_NAME	"clock-type"
+#define FDP_DP_CLOCK_FREQ_NAME	"clock-freq"
+#define FDP_DP_FW_VSC_CFG_NAME	"fw-vsc-cfg"
+
+#define FDP_FRAME_HEADROOM	2
+#define FDP_FRAME_TAILROOM	1
+
+#define FDP_NCI_I2C_MIN_PAYLOAD	5
+#define FDP_NCI_I2C_MAX_PAYLOAD	261
+
+#define FDP_POWER_OFF		0
+#define FDP_POWER_ON		1
+
+#define fdp_nci_i2c_dump_skb(dev, prefix, skb)				\
+	print_hex_dump(KERN_DEBUG, prefix": ", DUMP_PREFIX_OFFSET,	\
+		       16, 1, (skb)->data, (skb)->len, 0)
+
+static void fdp_nci_i2c_reset(const struct fdp_i2c_phy *phy)
+{
+	/* Reset RST/WakeUP for at least 100 micro-second */
+	gpiod_set_value_cansleep(phy->power_gpio, FDP_POWER_OFF);
+	usleep_range(1000, 4000);
+	gpiod_set_value_cansleep(phy->power_gpio, FDP_POWER_ON);
+	usleep_range(10000, 14000);
+}
+
+static int fdp_nci_i2c_enable(void *phy_id)
+{
+	const struct fdp_i2c_phy *phy = phy_id;
+
+	fdp_nci_i2c_reset(phy);
+
+	return 0;
+}
+
+static void fdp_nci_i2c_disable(void *phy_id)
+{
+	const struct fdp_i2c_phy *phy = phy_id;
+
+	fdp_nci_i2c_reset(phy);
+}
+
+static void fdp_nci_i2c_add_len_lrc(struct sk_buff *skb)
+{
+	u8 lrc = 0;
+	u16 len, i;
+
+	/* Add length header */
+	len = skb->len;
+	*(u8 *)skb_push(skb, 1) = len & 0xff;
+	*(u8 *)skb_push(skb, 1) = len >> 8;
+
+	/* Compute and add lrc */
+	for (i = 0; i < len + 2; i++)
+		lrc ^= skb->data[i];
+
+	skb_put_u8(skb, lrc);
+}
+
+static void fdp_nci_i2c_remove_len_lrc(struct sk_buff *skb)
+{
+	skb_pull(skb, FDP_FRAME_HEADROOM);
+	skb_trim(skb, skb->len - FDP_FRAME_TAILROOM);
+}
+
+static int fdp_nci_i2c_write(void *phy_id, struct sk_buff *skb)
+{
+	struct fdp_i2c_phy *phy = phy_id;
+	struct i2c_client *client = phy->i2c_dev;
+	int r;
+
+	if (phy->hard_fault != 0)
+		return phy->hard_fault;
+
+	fdp_nci_i2c_add_len_lrc(skb);
+	fdp_nci_i2c_dump_skb(&client->dev, "fdp_wr", skb);
+
+	r = i2c_master_send(client, skb->data, skb->len);
+	if (r == -EREMOTEIO) {  /* Retry, chip was in standby */
+		usleep_range(1000, 4000);
+		r = i2c_master_send(client, skb->data, skb->len);
+	}
+
+	if (r < 0 || r != skb->len)
+		dev_dbg(&client->dev, "%s: error err=%d len=%d\n",
+			__func__, r, skb->len);
+
+	if (r >= 0) {
+		if (r != skb->len) {
+			phy->hard_fault = r;
+			r = -EREMOTEIO;
+		} else {
+			r = 0;
+		}
+	}
+
+	fdp_nci_i2c_remove_len_lrc(skb);
+
+	return r;
+}
+
+static const struct nfc_phy_ops i2c_phy_ops = {
+	.write = fdp_nci_i2c_write,
+	.enable = fdp_nci_i2c_enable,
+	.disable = fdp_nci_i2c_disable,
+};
+
+static int fdp_nci_i2c_read(struct fdp_i2c_phy *phy, struct sk_buff **skb)
+{
+	int r, len;
+	u8 tmp[FDP_NCI_I2C_MAX_PAYLOAD], lrc, k;
+	u16 i;
+	struct i2c_client *client = phy->i2c_dev;
+
+	*skb = NULL;
+
+	/* Read the length packet and the data packet */
+	for (k = 0; k < 2; k++) {
+
+		len = phy->next_read_size;
+
+		r = i2c_master_recv(client, tmp, len);
+		if (r != len) {
+			dev_dbg(&client->dev, "%s: i2c recv err: %d\n",
+				__func__, r);
+			goto flush;
+		}
+
+		/* Check packet integruty */
+		for (lrc = i = 0; i < r; i++)
+			lrc ^= tmp[i];
+
+		/*
+		 * LRC check failed. This may due to transmission error or
+		 * desynchronization between driver and FDP. Drop the packet
+		 * and force resynchronization
+		 */
+		if (lrc) {
+			dev_dbg(&client->dev, "%s: corrupted packet\n",
+				__func__);
+			phy->next_read_size = 5;
+			goto flush;
+		}
+
+		/* Packet that contains a length */
+		if (tmp[0] == 0 && tmp[1] == 0) {
+			phy->next_read_size = (tmp[2] << 8) + tmp[3] + 3;
+		} else {
+			phy->next_read_size = FDP_NCI_I2C_MIN_PAYLOAD;
+
+			*skb = alloc_skb(len, GFP_KERNEL);
+			if (*skb == NULL) {
+				r = -ENOMEM;
+				goto flush;
+			}
+
+			skb_put_data(*skb, tmp, len);
+			fdp_nci_i2c_dump_skb(&client->dev, "fdp_rd", *skb);
+
+			fdp_nci_i2c_remove_len_lrc(*skb);
+		}
+	}
+
+	return 0;
+
+flush:
+	/* Flush the remaining data */
+	if (i2c_master_recv(client, tmp, sizeof(tmp)) < 0)
+		r = -EREMOTEIO;
+
+	return r;
+}
+
+static irqreturn_t fdp_nci_i2c_irq_thread_fn(int irq, void *phy_id)
+{
+	struct fdp_i2c_phy *phy = phy_id;
+	struct sk_buff *skb;
+	int r;
+
+	if (!phy || irq != phy->i2c_dev->irq) {
+		WARN_ON_ONCE(1);
+		return IRQ_NONE;
+	}
+
+	r = fdp_nci_i2c_read(phy, &skb);
+
+	if (r == -EREMOTEIO || r == -ENOMEM || r == -EBADMSG)
+		return IRQ_HANDLED;
+
+	if (skb != NULL)
+		nci_recv_frame(phy->ndev, skb);
+
+	return IRQ_HANDLED;
+}
+
+static void fdp_nci_i2c_read_device_properties(struct device *dev,
+					       u8 *clock_type, u32 *clock_freq,
+					       u8 **fw_vsc_cfg)
+{
+	int r;
+	u8 len;
+
+	r = device_property_read_u8(dev, FDP_DP_CLOCK_TYPE_NAME, clock_type);
+	if (r) {
+		dev_dbg(dev, "Using default clock type");
+		*clock_type = 0;
+	}
+
+	r = device_property_read_u32(dev, FDP_DP_CLOCK_FREQ_NAME, clock_freq);
+	if (r) {
+		dev_dbg(dev, "Using default clock frequency\n");
+		*clock_freq = 26000;
+	}
+
+	if (device_property_present(dev, FDP_DP_FW_VSC_CFG_NAME)) {
+		r = device_property_read_u8(dev, FDP_DP_FW_VSC_CFG_NAME,
+					    &len);
+
+		if (r || len <= 0)
+			goto vsc_read_err;
+
+		/* Add 1 to the length to inclue the length byte itself */
+		len++;
+
+		*fw_vsc_cfg = devm_kmalloc_array(dev,
+					   len, sizeof(**fw_vsc_cfg),
+					   GFP_KERNEL);
+
+		if (!*fw_vsc_cfg)
+			goto alloc_err;
+
+		r = device_property_read_u8_array(dev, FDP_DP_FW_VSC_CFG_NAME,
+						  *fw_vsc_cfg, len);
+
+		if (r) {
+			devm_kfree(dev, *fw_vsc_cfg);
+			goto vsc_read_err;
+		}
+	} else {
+vsc_read_err:
+		dev_dbg(dev, "FW vendor specific commands not present\n");
+		*fw_vsc_cfg = NULL;
+	}
+
+alloc_err:
+	dev_dbg(dev, "Clock type: %d, clock frequency: %d, VSC: %s",
+		*clock_type, *clock_freq, *fw_vsc_cfg != NULL ? "yes" : "no");
+}
+
+static const struct acpi_gpio_params power_gpios = { 0, 0, false };
+
+static const struct acpi_gpio_mapping acpi_fdp_gpios[] = {
+	{ "power-gpios", &power_gpios, 1 },
+	{},
+};
+
+static int fdp_nci_i2c_probe(struct i2c_client *client)
+{
+	struct fdp_i2c_phy *phy;
+	struct device *dev = &client->dev;
+	u8 *fw_vsc_cfg;
+	u8 clock_type;
+	u32 clock_freq;
+	int r = 0;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
+		nfc_err(dev, "No I2C_FUNC_I2C support\n");
+		return -ENODEV;
+	}
+
+	/* Checking if we have an irq */
+	if (client->irq <= 0) {
+		nfc_err(dev, "IRQ not present\n");
+		return -ENODEV;
+	}
+
+	phy = devm_kzalloc(dev, sizeof(struct fdp_i2c_phy), GFP_KERNEL);
+	if (!phy)
+		return -ENOMEM;
+
+	phy->i2c_dev = client;
+	phy->next_read_size = FDP_NCI_I2C_MIN_PAYLOAD;
+	i2c_set_clientdata(client, phy);
+
+	r = devm_request_threaded_irq(dev, client->irq,
+				      NULL, fdp_nci_i2c_irq_thread_fn,
+				      IRQF_TRIGGER_RISING | IRQF_ONESHOT,
+				      FDP_I2C_DRIVER_NAME, phy);
+
+	if (r < 0) {
+		nfc_err(&client->dev, "Unable to register IRQ handler\n");
+		return r;
+	}
+
+	r = devm_acpi_dev_add_driver_gpios(dev, acpi_fdp_gpios);
+	if (r)
+		dev_dbg(dev, "Unable to add GPIO mapping table\n");
+
+	/* Requesting the power gpio */
+	phy->power_gpio = devm_gpiod_get(dev, "power", GPIOD_OUT_LOW);
+	if (IS_ERR(phy->power_gpio)) {
+		nfc_err(dev, "Power GPIO request failed\n");
+		return PTR_ERR(phy->power_gpio);
+	}
+
+	/* read device properties to get the clock and production settings */
+	fdp_nci_i2c_read_device_properties(dev, &clock_type, &clock_freq,
+					   &fw_vsc_cfg);
+
+	/* Call the NFC specific probe function */
+	r = fdp_nci_probe(phy, &i2c_phy_ops, &phy->ndev,
+			  FDP_FRAME_HEADROOM, FDP_FRAME_TAILROOM,
+			  clock_type, clock_freq, fw_vsc_cfg);
+	if (r < 0) {
+		nfc_err(dev, "NCI probing error\n");
+		return r;
+	}
+
+	return 0;
+}
+
+static void fdp_nci_i2c_remove(struct i2c_client *client)
+{
+	struct fdp_i2c_phy *phy = i2c_get_clientdata(client);
+
+	fdp_nci_remove(phy->ndev);
+	fdp_nci_i2c_disable(phy);
+}
+
+static const struct acpi_device_id fdp_nci_i2c_acpi_match[] = {
+	{"INT339A", 0},
+	{}
+};
+MODULE_DEVICE_TABLE(acpi, fdp_nci_i2c_acpi_match);
+
+static struct i2c_driver fdp_nci_i2c_driver = {
+	.driver = {
+		   .name = FDP_I2C_DRIVER_NAME,
+		   .acpi_match_table = fdp_nci_i2c_acpi_match,
+		  },
+	.probe = fdp_nci_i2c_probe,
+	.remove = fdp_nci_i2c_remove,
+};
+module_i2c_driver(fdp_nci_i2c_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("I2C driver for Intel Fields Peak NFC controller");
+MODULE_AUTHOR("Robert Dolca <robert.dolca@intel.com>");