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, 238 insertions, 0 deletions

diff --git a/sound/soc/codecs/rt-sdw-common.c b/sound/soc/codecs/rt-sdw-common.c
new file mode 100644
index 000000000..ad61943ce
--- /dev/null
+++ b/sound/soc/codecs/rt-sdw-common.c
@@ -0,0 +1,238 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// rt-sdw-common.c
+//
+// Copyright(c) 2024 Realtek Semiconductor Corp.
+//
+
+/*
+ * This file defines common functions used with Realtek soundwire codecs.
+ */
+
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/bitops.h>
+#include <linux/soundwire/sdw_registers.h>
+#include <sound/jack.h>
+
+#include "rt-sdw-common.h"
+
+/**
+ * rt_sdca_index_write - Write a value to Realtek defined register.
+ *
+ * @map: map for setting.
+ * @nid: Realtek-defined ID.
+ * @reg: register.
+ * @value: value.
+ *
+ * A value of zero will be returned on success, a negative errno will
+ * be returned in error cases.
+ */
+int rt_sdca_index_write(struct regmap *map, unsigned int nid,
+	unsigned int reg, unsigned int value)
+{
+	unsigned int addr = (nid << 20) | reg;
+	int ret;
+
+	ret = regmap_write(map, addr, value);
+	if (ret < 0)
+		pr_err("Failed to set value: %06x <= %04x ret=%d\n",
+			addr, value, ret);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rt_sdca_index_write);
+
+/**
+ * rt_sdca_index_read - Read value from Realtek defined register.
+ *
+ * @map: map for setting.
+ * @nid: Realtek-defined ID.
+ * @reg: register.
+ * @value: value.
+ *
+ * A value of zero will be returned on success, a negative errno will
+ * be returned in error cases.
+ */
+int rt_sdca_index_read(struct regmap *map, unsigned int nid,
+	unsigned int reg, unsigned int *value)
+{
+	unsigned int addr = (nid << 20) | reg;
+	int ret;
+
+	ret = regmap_read(map, addr, value);
+	if (ret < 0)
+		pr_err("Failed to get value: %06x => %04x ret=%d\n",
+			addr, *value, ret);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rt_sdca_index_read);
+
+/**
+ * rt_sdca_index_update_bits - Update value on Realtek defined register.
+ *
+ * @map: map for setting.
+ * @nid: Realtek-defined ID.
+ * @reg: register.
+ * @mask: Bitmask to change
+ * @val: New value for bitmask
+ *
+ * A value of zero will be returned on success, a negative errno will
+ * be returned in error cases.
+ */
+
+int rt_sdca_index_update_bits(struct regmap *map,
+	unsigned int nid, unsigned int reg, unsigned int mask, unsigned int val)
+{
+	unsigned int tmp;
+	int ret;
+
+	ret = rt_sdca_index_read(map, nid, reg, &tmp);
+	if (ret < 0)
+		return ret;
+
+	set_mask_bits(&tmp, mask, val);
+	return rt_sdca_index_write(map, nid, reg, tmp);
+}
+EXPORT_SYMBOL_GPL(rt_sdca_index_update_bits);
+
+/**
+ * rt_sdca_btn_type - Decision of button type.
+ *
+ * @buffer: UMP message buffer.
+ *
+ * A button type will be returned regarding to buffer,
+ * it returns zero if buffer cannot be recognized.
+ */
+int rt_sdca_btn_type(unsigned char *buffer)
+{
+	u8 btn_type = 0;
+	int ret = 0;
+
+	btn_type |= buffer[0] & 0xf;
+	btn_type |= (buffer[0] >> 4) & 0xf;
+	btn_type |= buffer[1] & 0xf;
+	btn_type |= (buffer[1] >> 4) & 0xf;
+
+	if (btn_type & BIT(0))
+		ret |= SND_JACK_BTN_2;
+	if (btn_type & BIT(1))
+		ret |= SND_JACK_BTN_3;
+	if (btn_type & BIT(2))
+		ret |= SND_JACK_BTN_0;
+	if (btn_type & BIT(3))
+		ret |= SND_JACK_BTN_1;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rt_sdca_btn_type);
+
+/**
+ * rt_sdca_headset_detect - Headset jack type detection.
+ *
+ * @map: map for setting.
+ * @entity_id: SDCA entity ID.
+ *
+ * A headset jack type will be returned, a negative errno will
+ * be returned in error cases.
+ */
+int rt_sdca_headset_detect(struct regmap *map, unsigned int entity_id)
+{
+	unsigned int det_mode, jack_type;
+	int ret;
+
+	/* get detected_mode */
+	ret = regmap_read(map, SDW_SDCA_CTL(SDCA_NUM_JACK_CODEC, entity_id,
+			RT_SDCA_CTL_DETECTED_MODE, 0), &det_mode);
+
+	if (ret < 0)
+		goto io_error;
+
+	switch (det_mode) {
+	case 0x03:
+		jack_type = SND_JACK_HEADPHONE;
+		break;
+	case 0x05:
+		jack_type = SND_JACK_HEADSET;
+		break;
+	default:
+		jack_type = 0;
+		break;
+	}
+
+	/* write selected_mode */
+	if (det_mode) {
+		ret = regmap_write(map, SDW_SDCA_CTL(SDCA_NUM_JACK_CODEC, entity_id,
+				RT_SDCA_CTL_SELECTED_MODE, 0), det_mode);
+		if (ret < 0)
+			goto io_error;
+	}
+
+	return jack_type;
+
+io_error:
+	pr_err_ratelimited("IO error in %s, ret %d\n", __func__, ret);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(rt_sdca_headset_detect);
+
+/**
+ * rt_sdca_button_detect - Read UMP message and decide button type.
+ *
+ * @map: map for setting.
+ * @entity_id: SDCA entity ID.
+ * @hid_buf_addr: HID buffer address.
+ * @hid_id: Report ID for HID.
+ *
+ * A button type will be returned regarding to buffer,
+ * it returns zero if buffer cannot be recognized.
+ */
+int rt_sdca_button_detect(struct regmap *map, unsigned int entity_id,
+	unsigned int hid_buf_addr, unsigned int hid_id)
+{
+	unsigned int btn_type = 0, offset, idx, val, owner;
+	unsigned char buf[3];
+	int ret;
+
+	/* get current UMP message owner */
+	ret = regmap_read(map, SDW_SDCA_CTL(SDCA_NUM_HID, entity_id,
+			RT_SDCA_CTL_HIDTX_CURRENT_OWNER, 0), &owner);
+	if (ret < 0)
+		return 0;
+
+	/* if owner is device then there is no button event from device */
+	if (owner == 1)
+		return 0;
+
+	/* read UMP message offset */
+	ret = regmap_read(map, SDW_SDCA_CTL(SDCA_NUM_HID, entity_id,
+			RT_SDCA_CTL_HIDTX_MESSAGE_OFFSET, 0), &offset);
+	if (ret < 0)
+		goto _end_btn_det_;
+
+	for (idx = 0; idx < sizeof(buf); idx++) {
+		ret = regmap_read(map, hid_buf_addr + offset + idx, &val);
+		if (ret < 0)
+			goto _end_btn_det_;
+		buf[idx] = val & 0xff;
+	}
+	/* Report ID for HID */
+	if (buf[0] == hid_id)
+		btn_type = rt_sdca_btn_type(&buf[1]);
+
+_end_btn_det_:
+	/* Host is owner, so set back to device */
+	if (owner == 0)
+		/* set owner to device */
+		regmap_write(map,
+			SDW_SDCA_CTL(SDCA_NUM_HID, entity_id,
+				RT_SDCA_CTL_HIDTX_CURRENT_OWNER, 0), 0x01);
+
+	return btn_type;
+}
+EXPORT_SYMBOL_GPL(rt_sdca_button_detect);
+
+MODULE_DESCRIPTION("Realtek soundwire common functions");
+MODULE_AUTHOR("jack yu <jack.yu@realtek.com>");
+MODULE_LICENSE("GPL");