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, 258 insertions, 0 deletions

diff --git a/drivers/phy/phy-can-transceiver.c b/drivers/phy/phy-can-transceiver.c
new file mode 100644
index 000000000..75dc49e75
--- /dev/null
+++ b/drivers/phy/phy-can-transceiver.c
@@ -0,0 +1,258 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * phy-can-transceiver.c - phy driver for CAN transceivers
+ *
+ * Copyright (C) 2021 Texas Instruments Incorporated - https://www.ti.com
+ *
+ */
+#include <linux/gpio/consumer.h>
+#include <linux/phy/phy.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/module.h>
+#include <linux/mux/consumer.h>
+
+struct can_transceiver_data {
+	u32 flags;
+#define CAN_TRANSCEIVER_STB_PRESENT	BIT(0)
+#define CAN_TRANSCEIVER_EN_PRESENT	BIT(1)
+#define CAN_TRANSCEIVER_DUAL_CH		BIT(2)
+#define CAN_TRANSCEIVER_SILENT_PRESENT	BIT(3)
+};
+
+struct can_transceiver_phy {
+	struct phy *generic_phy;
+	struct gpio_desc *silent_gpio;
+	struct gpio_desc *standby_gpio;
+	struct gpio_desc *enable_gpio;
+	struct can_transceiver_priv *priv;
+};
+
+struct can_transceiver_priv {
+	struct mux_state *mux_state;
+	int num_ch;
+	struct can_transceiver_phy can_transceiver_phy[] __counted_by(num_ch);
+};
+
+/* Power on function */
+static int can_transceiver_phy_power_on(struct phy *phy)
+{
+	struct can_transceiver_phy *can_transceiver_phy = phy_get_drvdata(phy);
+	struct can_transceiver_priv *priv = can_transceiver_phy->priv;
+	int ret;
+
+	if (priv->mux_state) {
+		ret = mux_state_select(priv->mux_state);
+		if (ret) {
+			dev_err(&phy->dev, "Failed to select CAN mux: %d\n", ret);
+			return ret;
+		}
+	}
+	gpiod_set_value_cansleep(can_transceiver_phy->silent_gpio, 0);
+	gpiod_set_value_cansleep(can_transceiver_phy->standby_gpio, 0);
+	gpiod_set_value_cansleep(can_transceiver_phy->enable_gpio, 1);
+
+	return 0;
+}
+
+/* Power off function */
+static int can_transceiver_phy_power_off(struct phy *phy)
+{
+	struct can_transceiver_phy *can_transceiver_phy = phy_get_drvdata(phy);
+	struct can_transceiver_priv *priv = can_transceiver_phy->priv;
+
+	gpiod_set_value_cansleep(can_transceiver_phy->silent_gpio, 1);
+	gpiod_set_value_cansleep(can_transceiver_phy->standby_gpio, 1);
+	gpiod_set_value_cansleep(can_transceiver_phy->enable_gpio, 0);
+	if (priv->mux_state)
+		mux_state_deselect(priv->mux_state);
+
+	return 0;
+}
+
+static const struct phy_ops can_transceiver_phy_ops = {
+	.power_on	= can_transceiver_phy_power_on,
+	.power_off	= can_transceiver_phy_power_off,
+	.owner		= THIS_MODULE,
+};
+
+static const struct can_transceiver_data tcan1042_drvdata = {
+	.flags = CAN_TRANSCEIVER_STB_PRESENT,
+};
+
+static const struct can_transceiver_data tcan1043_drvdata = {
+	.flags = CAN_TRANSCEIVER_STB_PRESENT | CAN_TRANSCEIVER_EN_PRESENT,
+};
+
+static const struct can_transceiver_data tja1048_drvdata = {
+	.flags = CAN_TRANSCEIVER_STB_PRESENT | CAN_TRANSCEIVER_DUAL_CH,
+};
+
+static const struct can_transceiver_data tja1051_drvdata = {
+	.flags = CAN_TRANSCEIVER_SILENT_PRESENT | CAN_TRANSCEIVER_EN_PRESENT,
+};
+
+static const struct can_transceiver_data tja1057_drvdata = {
+	.flags = CAN_TRANSCEIVER_SILENT_PRESENT,
+};
+
+static struct phy *can_transceiver_phy_xlate(struct device *dev,
+					     const struct of_phandle_args *args)
+{
+	struct can_transceiver_priv *priv = dev_get_drvdata(dev);
+	u32 idx;
+
+	if (priv->num_ch == 1)
+		return priv->can_transceiver_phy[0].generic_phy;
+
+	if (args->args_count != 1)
+		return ERR_PTR(-EINVAL);
+
+	idx = args->args[0];
+	if (idx >= priv->num_ch)
+		return ERR_PTR(-EINVAL);
+
+	return priv->can_transceiver_phy[idx].generic_phy;
+}
+
+static int can_transceiver_phy_probe(struct platform_device *pdev)
+{
+	struct phy_provider *phy_provider;
+	struct device *dev = &pdev->dev;
+	struct can_transceiver_phy *can_transceiver_phy;
+	struct can_transceiver_priv *priv;
+	const struct can_transceiver_data *drvdata;
+	struct phy *phy;
+	struct gpio_desc *silent_gpio;
+	struct gpio_desc *standby_gpio;
+	struct gpio_desc *enable_gpio;
+	struct mux_state *mux_state;
+	const char *propname;
+	int err, i, num_ch;
+	u32 max_bitrate;
+
+	drvdata = device_get_match_data(dev);
+	if (!drvdata)
+		return -ENODEV;
+
+	if (drvdata->flags & CAN_TRANSCEIVER_DUAL_CH)
+		num_ch = 2;
+	else
+		num_ch = 1;
+
+	priv = devm_kzalloc(dev, struct_size(priv, can_transceiver_phy, num_ch), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->num_ch = num_ch;
+	platform_set_drvdata(pdev, priv);
+
+	mux_state = devm_mux_state_get_optional(dev, NULL);
+	if (IS_ERR(mux_state))
+		return PTR_ERR(mux_state);
+
+	priv->mux_state = mux_state;
+
+	propname = "max-bitrate";
+	if (device_property_present(dev, propname)) {
+		err = device_property_read_u32(dev, propname, &max_bitrate);
+		if (err)
+			return dev_err_probe(dev, err, "failed to parse %s\n", propname);
+
+		if (max_bitrate == 0)
+			dev_warn(dev, "Invalid value for transceiver max bitrate. Ignoring bitrate limit\n");
+	} else {
+		max_bitrate = 0;
+	}
+
+	for (i = 0; i < num_ch; i++) {
+		can_transceiver_phy = &priv->can_transceiver_phy[i];
+		can_transceiver_phy->priv = priv;
+
+		phy = devm_phy_create(dev, NULL, &can_transceiver_phy_ops);
+		if (IS_ERR(phy)) {
+			dev_err(dev, "failed to create can transceiver phy\n");
+			return PTR_ERR(phy);
+		}
+
+		phy->attrs.max_link_rate = max_bitrate;
+
+		can_transceiver_phy->generic_phy = phy;
+		can_transceiver_phy->priv = priv;
+
+		if (drvdata->flags & CAN_TRANSCEIVER_STB_PRESENT) {
+			standby_gpio = devm_gpiod_get_index_optional(dev, "standby", i,
+								     GPIOD_OUT_HIGH);
+			if (IS_ERR(standby_gpio))
+				return PTR_ERR(standby_gpio);
+			can_transceiver_phy->standby_gpio = standby_gpio;
+		}
+
+		if (drvdata->flags & CAN_TRANSCEIVER_EN_PRESENT) {
+			enable_gpio = devm_gpiod_get_index_optional(dev, "enable", i,
+								    GPIOD_OUT_LOW);
+			if (IS_ERR(enable_gpio))
+				return PTR_ERR(enable_gpio);
+			can_transceiver_phy->enable_gpio = enable_gpio;
+		}
+
+		if (drvdata->flags & CAN_TRANSCEIVER_SILENT_PRESENT) {
+			silent_gpio = devm_gpiod_get_index_optional(dev, "silent", i,
+								    GPIOD_OUT_LOW);
+			if (IS_ERR(silent_gpio))
+				return PTR_ERR(silent_gpio);
+			can_transceiver_phy->silent_gpio = silent_gpio;
+		}
+
+		phy_set_drvdata(can_transceiver_phy->generic_phy, can_transceiver_phy);
+
+	}
+
+	phy_provider = devm_of_phy_provider_register(dev, can_transceiver_phy_xlate);
+
+	return PTR_ERR_OR_ZERO(phy_provider);
+}
+
+static const struct of_device_id can_transceiver_phy_ids[] = {
+	{
+		.compatible = "ti,tcan1042",
+		.data = &tcan1042_drvdata
+	},
+	{
+		.compatible = "ti,tcan1043",
+		.data = &tcan1043_drvdata
+	},
+	{
+		.compatible = "nxp,tja1048",
+		.data = &tja1048_drvdata
+	},
+	{
+		.compatible = "nxp,tja1051",
+		.data = &tja1051_drvdata
+	},
+	{
+		.compatible = "nxp,tja1057",
+		.data = &tja1057_drvdata
+	},
+	{
+		.compatible = "nxp,tjr1443",
+		.data = &tcan1043_drvdata
+	},
+	{ }
+};
+MODULE_DEVICE_TABLE(of, can_transceiver_phy_ids);
+
+static struct platform_driver can_transceiver_phy_driver = {
+	.probe = can_transceiver_phy_probe,
+	.driver = {
+		.name = "can-transceiver-phy",
+		.of_match_table = can_transceiver_phy_ids,
+	},
+};
+
+module_platform_driver(can_transceiver_phy_driver);
+
+MODULE_AUTHOR("Faiz Abbas <faiz_abbas@ti.com>");
+MODULE_AUTHOR("Aswath Govindraju <a-govindraju@ti.com>");
+MODULE_DESCRIPTION("CAN TRANSCEIVER PHY driver");
+MODULE_LICENSE("GPL v2");