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, 163 insertions, 0 deletions

diff --git a/drivers/usb/phy/phy-isp1301.c b/drivers/usb/phy/phy-isp1301.c
new file mode 100644
index 000000000..73cc70e95
--- /dev/null
+++ b/drivers/usb/phy/phy-isp1301.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * NXP ISP1301 USB transceiver driver
+ *
+ * Copyright (C) 2012 Roland Stigge
+ *
+ * Author: Roland Stigge <stigge@antcom.de>
+ */
+
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/i2c.h>
+#include <linux/usb/phy.h>
+#include <linux/usb/isp1301.h>
+
+#define DRV_NAME		"isp1301"
+
+struct isp1301 {
+	struct usb_phy		phy;
+	struct mutex		mutex;
+
+	struct i2c_client	*client;
+};
+
+#define phy_to_isp(p)		(container_of((p), struct isp1301, phy))
+
+static const struct i2c_device_id isp1301_id[] = {
+	{ .name = "isp1301" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, isp1301_id);
+
+static const struct of_device_id isp1301_of_match[] = {
+	{.compatible = "nxp,isp1301" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, isp1301_of_match);
+
+static struct i2c_client *isp1301_i2c_client;
+
+static int __isp1301_write(struct isp1301 *isp, u8 reg, u8 value, u8 clear)
+{
+	return i2c_smbus_write_byte_data(isp->client, reg | clear, value);
+}
+
+static int isp1301_write(struct isp1301 *isp, u8 reg, u8 value)
+{
+	return __isp1301_write(isp, reg, value, 0);
+}
+
+static int isp1301_clear(struct isp1301 *isp, u8 reg, u8 value)
+{
+	return __isp1301_write(isp, reg, value, ISP1301_I2C_REG_CLEAR_ADDR);
+}
+
+static int isp1301_phy_init(struct usb_phy *phy)
+{
+	struct isp1301 *isp = phy_to_isp(phy);
+
+	/* Disable transparent UART mode first */
+	isp1301_clear(isp, ISP1301_I2C_MODE_CONTROL_1, MC1_UART_EN);
+	isp1301_clear(isp, ISP1301_I2C_MODE_CONTROL_1, ~MC1_SPEED_REG);
+	isp1301_write(isp, ISP1301_I2C_MODE_CONTROL_1, MC1_SPEED_REG);
+	isp1301_clear(isp, ISP1301_I2C_MODE_CONTROL_2, ~0);
+	isp1301_write(isp, ISP1301_I2C_MODE_CONTROL_2, (MC2_BI_DI | MC2_PSW_EN
+				| MC2_SPD_SUSP_CTRL));
+
+	isp1301_clear(isp, ISP1301_I2C_OTG_CONTROL_1, ~0);
+	isp1301_write(isp, ISP1301_I2C_MODE_CONTROL_1, MC1_DAT_SE0);
+	isp1301_write(isp, ISP1301_I2C_OTG_CONTROL_1, (OTG1_DM_PULLDOWN
+				| OTG1_DP_PULLDOWN));
+	isp1301_clear(isp, ISP1301_I2C_OTG_CONTROL_1, (OTG1_DM_PULLUP
+				| OTG1_DP_PULLUP));
+
+	/* mask all interrupts */
+	isp1301_clear(isp, ISP1301_I2C_INTERRUPT_LATCH, ~0);
+	isp1301_clear(isp, ISP1301_I2C_INTERRUPT_FALLING, ~0);
+	isp1301_clear(isp, ISP1301_I2C_INTERRUPT_RISING, ~0);
+
+	return 0;
+}
+
+static int isp1301_phy_set_vbus(struct usb_phy *phy, int on)
+{
+	struct isp1301 *isp = phy_to_isp(phy);
+
+	if (on)
+		isp1301_write(isp, ISP1301_I2C_OTG_CONTROL_1, OTG1_VBUS_DRV);
+	else
+		isp1301_clear(isp, ISP1301_I2C_OTG_CONTROL_1, OTG1_VBUS_DRV);
+
+	return 0;
+}
+
+static int isp1301_probe(struct i2c_client *client)
+{
+	struct isp1301 *isp;
+	struct usb_phy *phy;
+
+	isp = devm_kzalloc(&client->dev, sizeof(*isp), GFP_KERNEL);
+	if (!isp)
+		return -ENOMEM;
+
+	isp->client = client;
+	mutex_init(&isp->mutex);
+
+	phy = &isp->phy;
+	phy->dev = &client->dev;
+	phy->label = DRV_NAME;
+	phy->init = isp1301_phy_init;
+	phy->set_vbus = isp1301_phy_set_vbus;
+	phy->type = USB_PHY_TYPE_USB2;
+
+	i2c_set_clientdata(client, isp);
+	usb_add_phy_dev(phy);
+
+	isp1301_i2c_client = client;
+
+	return 0;
+}
+
+static void isp1301_remove(struct i2c_client *client)
+{
+	struct isp1301 *isp = i2c_get_clientdata(client);
+
+	usb_remove_phy(&isp->phy);
+	isp1301_i2c_client = NULL;
+}
+
+static struct i2c_driver isp1301_driver = {
+	.driver = {
+		.name = DRV_NAME,
+		.of_match_table = isp1301_of_match,
+	},
+	.probe = isp1301_probe,
+	.remove = isp1301_remove,
+	.id_table = isp1301_id,
+};
+
+module_i2c_driver(isp1301_driver);
+
+struct i2c_client *isp1301_get_client(struct device_node *node)
+{
+	struct i2c_client *client;
+
+	/* reference of ISP1301 I2C node via DT */
+	client = of_find_i2c_device_by_node(node);
+	if (client)
+		return client;
+
+	/* non-DT: only one ISP1301 chip supported */
+	if (isp1301_i2c_client) {
+		get_device(&isp1301_i2c_client->dev);
+		return isp1301_i2c_client;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(isp1301_get_client);
+
+MODULE_AUTHOR("Roland Stigge <stigge@antcom.de>");
+MODULE_DESCRIPTION("NXP ISP1301 USB transceiver driver");
+MODULE_LICENSE("GPL");