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, 349 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/cy8ctma140.c b/drivers/input/touchscreen/cy8ctma140.c
new file mode 100644
index 000000000..0ac48eff3
--- /dev/null
+++ b/drivers/input/touchscreen/cy8ctma140.c
@@ -0,0 +1,349 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Driver for Cypress CY8CTMA140 (TMA140) touchscreen
+ * (C) 2020 Linus Walleij <linus.walleij@linaro.org>
+ * (C) 2007 Cypress
+ * (C) 2007 Google, Inc.
+ *
+ * Inspired by the tma140_skomer.c driver in the Samsung GT-S7710 code
+ * drop. The GT-S7710 is codenamed "Skomer", the code also indicates
+ * that the same touchscreen was used in a product called "Lucas".
+ *
+ * The code drop for GT-S7710 also contains a firmware downloader and
+ * 15 (!) versions of the firmware drop from Cypress. But here we assume
+ * the firmware got downloaded to the touchscreen flash successfully and
+ * just use it to read the fingers. The shipped vendor driver does the
+ * same.
+ */
+
+#include <linux/unaligned.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/input.h>
+#include <linux/input/touchscreen.h>
+#include <linux/input/mt.h>
+#include <linux/slab.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/i2c.h>
+#include <linux/regulator/consumer.h>
+#include <linux/delay.h>
+
+#define CY8CTMA140_NAME			"cy8ctma140"
+
+#define CY8CTMA140_MAX_FINGERS		4
+
+#define CY8CTMA140_GET_FINGERS		0x00
+#define CY8CTMA140_GET_FW_INFO		0x19
+
+/* This message also fits some bytes for touchkeys, if used */
+#define CY8CTMA140_PACKET_SIZE		31
+
+#define CY8CTMA140_INVALID_BUFFER_BIT	5
+
+struct cy8ctma140 {
+	struct input_dev *input;
+	struct touchscreen_properties props;
+	struct device *dev;
+	struct i2c_client *client;
+	struct regulator_bulk_data regulators[2];
+	u8 prev_fingers;
+	u8 prev_f1id;
+	u8 prev_f2id;
+};
+
+static void cy8ctma140_report(struct cy8ctma140 *ts, u8 *data, int n_fingers)
+{
+	static const u8 contact_offsets[] = { 0x03, 0x09, 0x10, 0x16 };
+	u8 *buf;
+	u16 x, y;
+	u8 w;
+	u8 id;
+	int slot;
+	int i;
+
+	for (i = 0; i < n_fingers; i++) {
+		buf = &data[contact_offsets[i]];
+
+		/*
+		 * Odd contacts have contact ID in the lower nibble of
+		 * the preceding byte, whereas even contacts have it in
+		 * the upper nibble of the following byte.
+		 */
+		id = i % 2 ? buf[-1] & 0x0f : buf[5] >> 4;
+		slot = input_mt_get_slot_by_key(ts->input, id);
+		if (slot < 0)
+			continue;
+
+		x = get_unaligned_be16(buf);
+		y = get_unaligned_be16(buf + 2);
+		w = buf[4];
+
+		dev_dbg(ts->dev, "finger %d: ID %02x (%d, %d) w: %d\n",
+			slot, id, x, y, w);
+
+		input_mt_slot(ts->input, slot);
+		input_mt_report_slot_state(ts->input, MT_TOOL_FINGER, true);
+		touchscreen_report_pos(ts->input, &ts->props, x, y, true);
+		input_report_abs(ts->input, ABS_MT_TOUCH_MAJOR, w);
+	}
+
+	input_mt_sync_frame(ts->input);
+	input_sync(ts->input);
+}
+
+static irqreturn_t cy8ctma140_irq_thread(int irq, void *d)
+{
+	struct cy8ctma140 *ts = d;
+	u8 cmdbuf[] = { CY8CTMA140_GET_FINGERS };
+	u8 buf[CY8CTMA140_PACKET_SIZE];
+	struct i2c_msg msg[] = {
+		{
+			.addr = ts->client->addr,
+			.flags = 0,
+			.len = sizeof(cmdbuf),
+			.buf = cmdbuf,
+		}, {
+			.addr = ts->client->addr,
+			.flags = I2C_M_RD,
+			.len = sizeof(buf),
+			.buf = buf,
+		},
+	};
+	u8 n_fingers;
+	int ret;
+
+	ret = i2c_transfer(ts->client->adapter, msg, ARRAY_SIZE(msg));
+	if (ret != ARRAY_SIZE(msg)) {
+		if (ret < 0)
+			dev_err(ts->dev, "error reading message: %d\n", ret);
+		else
+			dev_err(ts->dev, "wrong number of messages\n");
+		goto out;
+	}
+
+	if (buf[1] & BIT(CY8CTMA140_INVALID_BUFFER_BIT)) {
+		dev_dbg(ts->dev, "invalid event\n");
+		goto out;
+	}
+
+	n_fingers = buf[2] & 0x0f;
+	if (n_fingers > CY8CTMA140_MAX_FINGERS) {
+		dev_err(ts->dev, "unexpected number of fingers: %d\n",
+			n_fingers);
+		goto out;
+	}
+
+	cy8ctma140_report(ts, buf, n_fingers);
+
+out:
+	return IRQ_HANDLED;
+}
+
+static int cy8ctma140_init(struct cy8ctma140 *ts)
+{
+	u8 addr[1];
+	u8 buf[5];
+	int ret;
+
+	addr[0] = CY8CTMA140_GET_FW_INFO;
+	ret = i2c_master_send(ts->client, addr, 1);
+	if (ret < 0) {
+		dev_err(ts->dev, "error sending FW info message\n");
+		return ret;
+	}
+	ret = i2c_master_recv(ts->client, buf, 5);
+	if (ret < 0) {
+		dev_err(ts->dev, "error receiving FW info message\n");
+		return ret;
+	}
+	if (ret != 5) {
+		dev_err(ts->dev, "got only %d bytes\n", ret);
+		return -EIO;
+	}
+
+	dev_dbg(ts->dev, "vendor %c%c, HW ID %.2d, FW ver %.4d\n",
+		buf[0], buf[1], buf[3], buf[4]);
+
+	return 0;
+}
+
+static int cy8ctma140_power_up(struct cy8ctma140 *ts)
+{
+	int error;
+
+	error = regulator_bulk_enable(ARRAY_SIZE(ts->regulators),
+				      ts->regulators);
+	if (error) {
+		dev_err(ts->dev, "failed to enable regulators\n");
+		return error;
+	}
+
+	msleep(250);
+
+	return 0;
+}
+
+static void cy8ctma140_power_down(struct cy8ctma140 *ts)
+{
+	regulator_bulk_disable(ARRAY_SIZE(ts->regulators),
+			       ts->regulators);
+}
+
+/* Called from the registered devm action */
+static void cy8ctma140_power_off_action(void *d)
+{
+	struct cy8ctma140 *ts = d;
+
+	cy8ctma140_power_down(ts);
+}
+
+static int cy8ctma140_probe(struct i2c_client *client)
+{
+	struct cy8ctma140 *ts;
+	struct input_dev *input;
+	struct device *dev = &client->dev;
+	int error;
+
+	ts = devm_kzalloc(dev, sizeof(*ts), GFP_KERNEL);
+	if (!ts)
+		return -ENOMEM;
+
+	input = devm_input_allocate_device(dev);
+	if (!input)
+		return -ENOMEM;
+
+	ts->dev = dev;
+	ts->client = client;
+	ts->input = input;
+
+	input_set_capability(input, EV_ABS, ABS_MT_POSITION_X);
+	input_set_capability(input, EV_ABS, ABS_MT_POSITION_Y);
+	/* One byte for width 0..255 so this is the limit */
+	input_set_abs_params(input, ABS_MT_TOUCH_MAJOR, 0, 255, 0, 0);
+	/*
+	 * This sets up event max/min capabilities and fuzz.
+	 * Some DT properties are compulsory so we do not need
+	 * to provide defaults for X/Y max or pressure max.
+	 *
+	 * We just initialize a very simple MT touchscreen here,
+	 * some devices use the capability of this touchscreen to
+	 * provide touchkeys, and in that case this needs to be
+	 * extended to handle touchkey input.
+	 *
+	 * The firmware takes care of finger tracking and dropping
+	 * invalid ranges.
+	 */
+	touchscreen_parse_properties(input, true, &ts->props);
+	input_abs_set_fuzz(input, ABS_MT_POSITION_X, 0);
+	input_abs_set_fuzz(input, ABS_MT_POSITION_Y, 0);
+
+	error = input_mt_init_slots(input, CY8CTMA140_MAX_FINGERS,
+				  INPUT_MT_DIRECT | INPUT_MT_DROP_UNUSED);
+	if (error)
+		return error;
+
+	input->name = CY8CTMA140_NAME;
+	input->id.bustype = BUS_I2C;
+	input_set_drvdata(input, ts);
+
+	/*
+	 * VCPIN is the analog voltage supply
+	 * VDD is the digital voltage supply
+	 * since the voltage range of VDD overlaps that of VCPIN,
+	 * many designs to just supply both with a single voltage
+	 * source of ~3.3 V.
+	 */
+	ts->regulators[0].supply = "vcpin";
+	ts->regulators[1].supply = "vdd";
+	error = devm_regulator_bulk_get(dev, ARRAY_SIZE(ts->regulators),
+				      ts->regulators);
+	if (error)
+		return dev_err_probe(dev, error, "Failed to get regulators\n");
+
+	error = cy8ctma140_power_up(ts);
+	if (error)
+		return error;
+
+	error = devm_add_action_or_reset(dev, cy8ctma140_power_off_action, ts);
+	if (error) {
+		dev_err(dev, "failed to install power off handler\n");
+		return error;
+	}
+
+	error = devm_request_threaded_irq(dev, client->irq,
+					  NULL, cy8ctma140_irq_thread,
+					  IRQF_ONESHOT, CY8CTMA140_NAME, ts);
+	if (error) {
+		dev_err(dev, "irq %d busy? error %d\n", client->irq, error);
+		return error;
+	}
+
+	error = cy8ctma140_init(ts);
+	if (error)
+		return error;
+
+	error = input_register_device(input);
+	if (error)
+		return error;
+
+	i2c_set_clientdata(client, ts);
+
+	return 0;
+}
+
+static int cy8ctma140_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct cy8ctma140 *ts = i2c_get_clientdata(client);
+
+	if (!device_may_wakeup(&client->dev))
+		cy8ctma140_power_down(ts);
+
+	return 0;
+}
+
+static int cy8ctma140_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct cy8ctma140 *ts = i2c_get_clientdata(client);
+	int error;
+
+	if (!device_may_wakeup(&client->dev)) {
+		error = cy8ctma140_power_up(ts);
+		if (error)
+			return error;
+	}
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(cy8ctma140_pm,
+				cy8ctma140_suspend, cy8ctma140_resume);
+
+static const struct i2c_device_id cy8ctma140_idtable[] = {
+	{ .name = CY8CTMA140_NAME },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(i2c, cy8ctma140_idtable);
+
+static const struct of_device_id cy8ctma140_of_match[] = {
+	{ .compatible = "cypress,cy8ctma140", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, cy8ctma140_of_match);
+
+static struct i2c_driver cy8ctma140_driver = {
+	.driver		= {
+		.name	= CY8CTMA140_NAME,
+		.pm	= pm_sleep_ptr(&cy8ctma140_pm),
+		.of_match_table = cy8ctma140_of_match,
+	},
+	.id_table	= cy8ctma140_idtable,
+	.probe		= cy8ctma140_probe,
+};
+module_i2c_driver(cy8ctma140_driver);
+
+MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
+MODULE_DESCRIPTION("CY8CTMA140 TouchScreen Driver");
+MODULE_LICENSE("GPL v2");