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, 275 insertions, 0 deletions

diff --git a/drivers/usb/chipidea/otg.c b/drivers/usb/chipidea/otg.c
new file mode 100644
index 000000000..fecc7d7e2
--- /dev/null
+++ b/drivers/usb/chipidea/otg.c
@@ -0,0 +1,275 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * otg.c - ChipIdea USB IP core OTG driver
+ *
+ * Copyright (C) 2013 Freescale Semiconductor, Inc.
+ *
+ * Author: Peter Chen
+ */
+
+/*
+ * This file mainly handles otgsc register, OTG fsm operations for HNP and SRP
+ * are also included.
+ */
+
+#include <linux/usb/otg.h>
+#include <linux/usb/gadget.h>
+#include <linux/usb/chipidea.h>
+
+#include "ci.h"
+#include "bits.h"
+#include "otg.h"
+#include "otg_fsm.h"
+
+/**
+ * hw_read_otgsc - returns otgsc register bits value.
+ * @ci: the controller
+ * @mask: bitfield mask
+ */
+u32 hw_read_otgsc(struct ci_hdrc *ci, u32 mask)
+{
+	struct ci_hdrc_cable *cable;
+	u32 val = hw_read(ci, OP_OTGSC, mask);
+
+	/*
+	 * If using extcon framework for VBUS and/or ID signal
+	 * detection overwrite OTGSC register value
+	 */
+	cable = &ci->platdata->vbus_extcon;
+	if (!IS_ERR(cable->edev) || ci->role_switch) {
+		if (cable->changed)
+			val |= OTGSC_BSVIS;
+		else
+			val &= ~OTGSC_BSVIS;
+
+		if (cable->connected)
+			val |= OTGSC_BSV;
+		else
+			val &= ~OTGSC_BSV;
+
+		if (cable->enabled)
+			val |= OTGSC_BSVIE;
+		else
+			val &= ~OTGSC_BSVIE;
+	}
+
+	cable = &ci->platdata->id_extcon;
+	if (!IS_ERR(cable->edev) || ci->role_switch) {
+		if (cable->changed)
+			val |= OTGSC_IDIS;
+		else
+			val &= ~OTGSC_IDIS;
+
+		if (cable->connected)
+			val &= ~OTGSC_ID; /* host */
+		else
+			val |= OTGSC_ID; /* device */
+
+		if (cable->enabled)
+			val |= OTGSC_IDIE;
+		else
+			val &= ~OTGSC_IDIE;
+	}
+
+	return val & mask;
+}
+
+/**
+ * hw_write_otgsc - updates target bits of OTGSC register.
+ * @ci: the controller
+ * @mask: bitfield mask
+ * @data: to be written
+ */
+void hw_write_otgsc(struct ci_hdrc *ci, u32 mask, u32 data)
+{
+	struct ci_hdrc_cable *cable;
+
+	cable = &ci->platdata->vbus_extcon;
+	if (!IS_ERR(cable->edev) || ci->role_switch) {
+		if (data & mask & OTGSC_BSVIS)
+			cable->changed = false;
+
+		/* Don't enable vbus interrupt if using external notifier */
+		if (data & mask & OTGSC_BSVIE) {
+			cable->enabled = true;
+			data &= ~OTGSC_BSVIE;
+		} else if (mask & OTGSC_BSVIE) {
+			cable->enabled = false;
+		}
+	}
+
+	cable = &ci->platdata->id_extcon;
+	if (!IS_ERR(cable->edev) || ci->role_switch) {
+		if (data & mask & OTGSC_IDIS)
+			cable->changed = false;
+
+		/* Don't enable id interrupt if using external notifier */
+		if (data & mask & OTGSC_IDIE) {
+			cable->enabled = true;
+			data &= ~OTGSC_IDIE;
+		} else if (mask & OTGSC_IDIE) {
+			cable->enabled = false;
+		}
+	}
+
+	hw_write(ci, OP_OTGSC, mask | OTGSC_INT_STATUS_BITS, data);
+}
+
+/**
+ * ci_otg_role - pick role based on ID pin state
+ * @ci: the controller
+ */
+enum ci_role ci_otg_role(struct ci_hdrc *ci)
+{
+	enum ci_role role = hw_read_otgsc(ci, OTGSC_ID)
+		? CI_ROLE_GADGET
+		: CI_ROLE_HOST;
+
+	return role;
+}
+
+void ci_handle_vbus_change(struct ci_hdrc *ci)
+{
+	if (ci->role != CI_ROLE_GADGET)
+		return;
+
+	if (!ci->is_otg) {
+		if (ci->platdata->flags & CI_HDRC_FORCE_VBUS_ACTIVE_ALWAYS)
+			usb_gadget_vbus_connect(&ci->gadget);
+		return;
+	}
+
+	if (hw_read_otgsc(ci, OTGSC_BSV) && !ci->vbus_active)
+		usb_gadget_vbus_connect(&ci->gadget);
+	else if (!hw_read_otgsc(ci, OTGSC_BSV) && ci->vbus_active)
+		usb_gadget_vbus_disconnect(&ci->gadget);
+}
+
+/**
+ * hw_wait_vbus_lower_bsv - When we switch to device mode, the vbus value
+ *                          should be lower than OTGSC_BSV before connecting
+ *                          to host.
+ *
+ * @ci: the controller
+ *
+ * This function returns an error code if timeout
+ */
+static int hw_wait_vbus_lower_bsv(struct ci_hdrc *ci)
+{
+	unsigned long elapse = jiffies + msecs_to_jiffies(5000);
+	u32 mask = OTGSC_BSV;
+
+	while (hw_read_otgsc(ci, mask)) {
+		if (time_after(jiffies, elapse)) {
+			dev_err(ci->dev, "timeout waiting for %08x in OTGSC\n",
+					mask);
+			return -ETIMEDOUT;
+		}
+		msleep(20);
+	}
+
+	return 0;
+}
+
+void ci_handle_id_switch(struct ci_hdrc *ci)
+{
+	enum ci_role role;
+
+	mutex_lock(&ci->mutex);
+	role = ci_otg_role(ci);
+	if (role != ci->role) {
+		dev_dbg(ci->dev, "switching from %s to %s\n",
+			ci_role(ci)->name, ci->roles[role]->name);
+
+		if (ci->vbus_active && ci->role == CI_ROLE_GADGET)
+			/*
+			 * vbus disconnect event is lost due to role
+			 * switch occurs during system suspend.
+			 */
+			usb_gadget_vbus_disconnect(&ci->gadget);
+
+		ci_role_stop(ci);
+
+		if (role == CI_ROLE_GADGET && !ci->role_switch &&
+		    IS_ERR(ci->platdata->vbus_extcon.edev))
+			/*
+			 * Wait vbus lower than OTGSC_BSV before connecting
+			 * to host. If connecting status is from an external
+			 * connector instead of register, we don't need to
+			 * care vbus on the board, since it will not affect
+			 * external connector status.
+			 */
+			hw_wait_vbus_lower_bsv(ci);
+
+		ci_role_start(ci, role);
+		/* vbus change may have already occurred */
+		if (role == CI_ROLE_GADGET)
+			ci_handle_vbus_change(ci);
+	}
+	mutex_unlock(&ci->mutex);
+}
+/**
+ * ci_otg_work - perform otg (vbus/id) event handle
+ * @work: work struct
+ */
+static void ci_otg_work(struct work_struct *work)
+{
+	struct ci_hdrc *ci = container_of(work, struct ci_hdrc, work);
+
+	if (ci_otg_is_fsm_mode(ci) && !ci_otg_fsm_work(ci)) {
+		enable_irq(ci->irq);
+		return;
+	}
+
+	pm_runtime_get_sync(ci->dev);
+
+	if (ci->id_event) {
+		ci->id_event = false;
+		ci_handle_id_switch(ci);
+	}
+
+	if (ci->b_sess_valid_event) {
+		ci->b_sess_valid_event = false;
+		ci_handle_vbus_change(ci);
+	}
+
+	pm_runtime_put_sync(ci->dev);
+
+	enable_irq(ci->irq);
+}
+
+
+/**
+ * ci_hdrc_otg_init - initialize otg struct
+ * @ci: the controller
+ */
+int ci_hdrc_otg_init(struct ci_hdrc *ci)
+{
+	INIT_WORK(&ci->work, ci_otg_work);
+	ci->wq = create_freezable_workqueue("ci_otg");
+	if (!ci->wq) {
+		dev_err(ci->dev, "can't create workqueue\n");
+		return -ENODEV;
+	}
+
+	if (ci_otg_is_fsm_mode(ci))
+		return ci_hdrc_otg_fsm_init(ci);
+
+	return 0;
+}
+
+/**
+ * ci_hdrc_otg_destroy - destroy otg struct
+ * @ci: the controller
+ */
+void ci_hdrc_otg_destroy(struct ci_hdrc *ci)
+{
+	if (ci->wq)
+		destroy_workqueue(ci->wq);
+
+	/* Disable all OTG irq and clear status */
+	hw_write_otgsc(ci, OTGSC_INT_EN_BITS | OTGSC_INT_STATUS_BITS,
+						OTGSC_INT_STATUS_BITS);
+	if (ci_otg_is_fsm_mode(ci))
+		ci_hdrc_otg_fsm_remove(ci);
+}