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, 282 insertions, 0 deletions

diff --git a/drivers/phy/phy-lgm-usb.c b/drivers/phy/phy-lgm-usb.c
new file mode 100644
index 000000000..eb7c6fed2
--- /dev/null
+++ b/drivers/phy/phy-lgm-usb.c
@@ -0,0 +1,282 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Intel LGM USB PHY driver
+ *
+ * Copyright (C) 2020 Intel Corporation.
+ */
+
+#include <linux/bitfield.h>
+#include <linux/delay.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
+#include <linux/reset.h>
+#include <linux/usb/phy.h>
+#include <linux/workqueue.h>
+
+#define CTRL1_OFFSET		0x14
+#define SRAM_EXT_LD_DONE	BIT(25)
+#define SRAM_INIT_DONE		BIT(26)
+
+#define TCPC_OFFSET		0x1014
+#define TCPC_MUX_CTL		GENMASK(1, 0)
+#define MUX_NC			0
+#define MUX_USB			1
+#define MUX_DP			2
+#define MUX_USBDP		3
+#define TCPC_FLIPPED		BIT(2)
+#define TCPC_LOW_POWER_EN	BIT(3)
+#define TCPC_VALID		BIT(4)
+#define TCPC_CONN		\
+	(TCPC_VALID | FIELD_PREP(TCPC_MUX_CTL, MUX_USB))
+#define TCPC_DISCONN		\
+	(TCPC_VALID | FIELD_PREP(TCPC_MUX_CTL, MUX_NC) | TCPC_LOW_POWER_EN)
+
+static const char *const PHY_RESETS[] = { "phy31", "phy", };
+static const char *const CTL_RESETS[] = { "apb", "ctrl", };
+
+struct tca_apb {
+	struct reset_control *resets[ARRAY_SIZE(PHY_RESETS)];
+	struct regulator *vbus;
+	struct work_struct wk;
+	struct usb_phy phy;
+
+	bool regulator_enabled;
+	bool phy_initialized;
+	bool connected;
+};
+
+static int get_flipped(struct tca_apb *ta, bool *flipped)
+{
+	union extcon_property_value property;
+	int ret;
+
+	ret = extcon_get_property(ta->phy.edev, EXTCON_USB_HOST,
+				  EXTCON_PROP_USB_TYPEC_POLARITY, &property);
+	if (ret) {
+		dev_err(ta->phy.dev, "no polarity property from extcon\n");
+		return ret;
+	}
+
+	*flipped = property.intval;
+
+	return 0;
+}
+
+static int phy_init(struct usb_phy *phy)
+{
+	struct tca_apb *ta = container_of(phy, struct tca_apb, phy);
+	void __iomem *ctrl1 = phy->io_priv + CTRL1_OFFSET;
+	int val, ret, i;
+
+	if (ta->phy_initialized)
+		return 0;
+
+	for (i = 0; i < ARRAY_SIZE(PHY_RESETS); i++)
+		reset_control_deassert(ta->resets[i]);
+
+	ret = readl_poll_timeout(ctrl1, val, val & SRAM_INIT_DONE, 10, 10 * 1000);
+	if (ret) {
+		dev_err(ta->phy.dev, "SRAM init failed, 0x%x\n", val);
+		return ret;
+	}
+
+	writel(readl(ctrl1) | SRAM_EXT_LD_DONE, ctrl1);
+
+	ta->phy_initialized = true;
+	if (!ta->phy.edev) {
+		writel(TCPC_CONN, ta->phy.io_priv + TCPC_OFFSET);
+		return phy->set_vbus(phy, true);
+	}
+
+	schedule_work(&ta->wk);
+
+	return ret;
+}
+
+static void phy_shutdown(struct usb_phy *phy)
+{
+	struct tca_apb *ta = container_of(phy, struct tca_apb, phy);
+	int i;
+
+	if (!ta->phy_initialized)
+		return;
+
+	ta->phy_initialized = false;
+	flush_work(&ta->wk);
+	ta->phy.set_vbus(&ta->phy, false);
+
+	ta->connected = false;
+	writel(TCPC_DISCONN, ta->phy.io_priv + TCPC_OFFSET);
+
+	for (i = 0; i < ARRAY_SIZE(PHY_RESETS); i++)
+		reset_control_assert(ta->resets[i]);
+}
+
+static int phy_set_vbus(struct usb_phy *phy, int on)
+{
+	struct tca_apb *ta = container_of(phy, struct tca_apb, phy);
+	int ret;
+
+	if (!!on == ta->regulator_enabled)
+		return 0;
+
+	if (on)
+		ret = regulator_enable(ta->vbus);
+	else
+		ret = regulator_disable(ta->vbus);
+
+	if (!ret)
+		ta->regulator_enabled = on;
+
+	dev_dbg(ta->phy.dev, "set vbus: %d\n", on);
+	return ret;
+}
+
+static void tca_work(struct work_struct *work)
+{
+	struct tca_apb *ta = container_of(work, struct tca_apb, wk);
+	bool connected;
+	bool flipped = false;
+	u32 val;
+	int ret;
+
+	ret = get_flipped(ta, &flipped);
+	if (ret)
+		return;
+
+	connected = extcon_get_state(ta->phy.edev, EXTCON_USB_HOST);
+	if (connected == ta->connected)
+		return;
+
+	ta->connected = connected;
+	if (connected) {
+		val = TCPC_CONN;
+		if (flipped)
+			val |= TCPC_FLIPPED;
+		dev_dbg(ta->phy.dev, "connected%s\n", flipped ? " flipped" : "");
+	} else {
+		val = TCPC_DISCONN;
+		dev_dbg(ta->phy.dev, "disconnected\n");
+	}
+
+	writel(val, ta->phy.io_priv + TCPC_OFFSET);
+
+	ret = ta->phy.set_vbus(&ta->phy, connected);
+	if (ret)
+		dev_err(ta->phy.dev, "failed to set VBUS\n");
+}
+
+static int id_notifier(struct notifier_block *nb, unsigned long event, void *ptr)
+{
+	struct tca_apb *ta = container_of(nb, struct tca_apb, phy.id_nb);
+
+	if (ta->phy_initialized)
+		schedule_work(&ta->wk);
+
+	return NOTIFY_DONE;
+}
+
+static int vbus_notifier(struct notifier_block *nb, unsigned long evnt, void *ptr)
+{
+	return NOTIFY_DONE;
+}
+
+static int phy_probe(struct platform_device *pdev)
+{
+	struct reset_control *resets[ARRAY_SIZE(CTL_RESETS)];
+	struct device *dev = &pdev->dev;
+	struct usb_phy *phy;
+	struct tca_apb *ta;
+	int i;
+
+	ta = devm_kzalloc(dev, sizeof(*ta), GFP_KERNEL);
+	if (!ta)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, ta);
+	INIT_WORK(&ta->wk, tca_work);
+
+	phy = &ta->phy;
+	phy->dev = dev;
+	phy->label = dev_name(dev);
+	phy->type = USB_PHY_TYPE_USB3;
+	phy->init = phy_init;
+	phy->shutdown = phy_shutdown;
+	phy->set_vbus = phy_set_vbus;
+	phy->id_nb.notifier_call = id_notifier;
+	phy->vbus_nb.notifier_call = vbus_notifier;
+
+	phy->io_priv = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(phy->io_priv))
+		return PTR_ERR(phy->io_priv);
+
+	ta->vbus = devm_regulator_get(dev, "vbus");
+	if (IS_ERR(ta->vbus))
+		return PTR_ERR(ta->vbus);
+
+	for (i = 0; i < ARRAY_SIZE(CTL_RESETS); i++) {
+		resets[i] = devm_reset_control_get_exclusive(dev, CTL_RESETS[i]);
+		if (IS_ERR(resets[i])) {
+			dev_err(dev, "%s reset not found\n", CTL_RESETS[i]);
+			return PTR_ERR(resets[i]);
+		}
+	}
+
+	for (i = 0; i < ARRAY_SIZE(PHY_RESETS); i++) {
+		ta->resets[i] = devm_reset_control_get_exclusive(dev, PHY_RESETS[i]);
+		if (IS_ERR(ta->resets[i])) {
+			dev_err(dev, "%s reset not found\n", PHY_RESETS[i]);
+			return PTR_ERR(ta->resets[i]);
+		}
+	}
+
+	for (i = 0; i < ARRAY_SIZE(CTL_RESETS); i++)
+		reset_control_assert(resets[i]);
+
+	for (i = 0; i < ARRAY_SIZE(PHY_RESETS); i++)
+		reset_control_assert(ta->resets[i]);
+	/*
+	 * Out-of-band reset of the controller after PHY reset will cause
+	 * controller malfunctioning, so we should use in-band controller
+	 * reset only and leave the controller de-asserted here.
+	 */
+	for (i = 0; i < ARRAY_SIZE(CTL_RESETS); i++)
+		reset_control_deassert(resets[i]);
+
+	/* Need to wait at least 20us after de-assert the controller */
+	usleep_range(20, 100);
+
+	return usb_add_phy_dev(phy);
+}
+
+static void phy_remove(struct platform_device *pdev)
+{
+	struct tca_apb *ta = platform_get_drvdata(pdev);
+
+	usb_remove_phy(&ta->phy);
+}
+
+static const struct of_device_id intel_usb_phy_dt_ids[] = {
+	{ .compatible = "intel,lgm-usb-phy" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, intel_usb_phy_dt_ids);
+
+static struct platform_driver lgm_phy_driver = {
+	.driver = {
+		.name = "lgm-usb-phy",
+		.of_match_table = intel_usb_phy_dt_ids,
+	},
+	.probe = phy_probe,
+	.remove = phy_remove,
+};
+
+module_platform_driver(lgm_phy_driver);
+
+MODULE_DESCRIPTION("Intel LGM USB PHY driver");
+MODULE_AUTHOR("Li Yin <yin1.li@intel.com>");
+MODULE_AUTHOR("Vadivel Murugan R <vadivel.muruganx.ramuthevar@linux.intel.com>");
+MODULE_LICENSE("GPL v2");