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, 298 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/88pm860x-ts.c b/drivers/input/touchscreen/88pm860x-ts.c
new file mode 100644
index 000000000..0468ce2b2
--- /dev/null
+++ b/drivers/input/touchscreen/88pm860x-ts.c
@@ -0,0 +1,298 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Touchscreen driver for Marvell 88PM860x
+ *
+ * Copyright (C) 2009 Marvell International Ltd.
+ * 	Haojian Zhuang <haojian.zhuang@marvell.com>
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/i2c.h>
+#include <linux/input.h>
+#include <linux/mfd/88pm860x.h>
+#include <linux/slab.h>
+#include <linux/device.h>
+
+#define MEAS_LEN		(8)
+#define ACCURATE_BIT		(12)
+
+/* touch register */
+#define MEAS_EN3		(0x52)
+
+#define MEAS_TSIX_1		(0x8D)
+#define MEAS_TSIX_2		(0x8E)
+#define MEAS_TSIY_1		(0x8F)
+#define MEAS_TSIY_2		(0x90)
+#define MEAS_TSIZ1_1		(0x91)
+#define MEAS_TSIZ1_2		(0x92)
+#define MEAS_TSIZ2_1		(0x93)
+#define MEAS_TSIZ2_2		(0x94)
+
+/* bit definitions of touch */
+#define MEAS_PD_EN		(1 << 3)
+#define MEAS_TSIX_EN		(1 << 4)
+#define MEAS_TSIY_EN		(1 << 5)
+#define MEAS_TSIZ1_EN		(1 << 6)
+#define MEAS_TSIZ2_EN		(1 << 7)
+
+struct pm860x_touch {
+	struct input_dev *idev;
+	struct i2c_client *i2c;
+	struct pm860x_chip *chip;
+	int irq;
+	int res_x;		/* resistor of Xplate */
+};
+
+static irqreturn_t pm860x_touch_handler(int irq, void *data)
+{
+	struct pm860x_touch *touch = data;
+	struct pm860x_chip *chip = touch->chip;
+	unsigned char buf[MEAS_LEN];
+	int x, y, pen_down;
+	int z1, z2, rt = 0;
+	int ret;
+
+	ret = pm860x_bulk_read(touch->i2c, MEAS_TSIX_1, MEAS_LEN, buf);
+	if (ret < 0)
+		goto out;
+
+	pen_down = buf[1] & (1 << 6);
+	x = ((buf[0] & 0xFF) << 4) | (buf[1] & 0x0F);
+	y = ((buf[2] & 0xFF) << 4) | (buf[3] & 0x0F);
+	z1 = ((buf[4] & 0xFF) << 4) | (buf[5] & 0x0F);
+	z2 = ((buf[6] & 0xFF) << 4) | (buf[7] & 0x0F);
+
+	if (pen_down) {
+		if ((x != 0) && (z1 != 0) && (touch->res_x != 0)) {
+			rt = z2 / z1 - 1;
+			rt = (rt * touch->res_x * x) >> ACCURATE_BIT;
+			dev_dbg(chip->dev, "z1:%d, z2:%d, rt:%d\n",
+				z1, z2, rt);
+		}
+		input_report_abs(touch->idev, ABS_X, x);
+		input_report_abs(touch->idev, ABS_Y, y);
+		input_report_abs(touch->idev, ABS_PRESSURE, rt);
+		input_report_key(touch->idev, BTN_TOUCH, 1);
+		dev_dbg(chip->dev, "pen down at [%d, %d].\n", x, y);
+	} else {
+		input_report_abs(touch->idev, ABS_PRESSURE, 0);
+		input_report_key(touch->idev, BTN_TOUCH, 0);
+		dev_dbg(chip->dev, "pen release\n");
+	}
+	input_sync(touch->idev);
+
+out:
+	return IRQ_HANDLED;
+}
+
+static int pm860x_touch_open(struct input_dev *dev)
+{
+	struct pm860x_touch *touch = input_get_drvdata(dev);
+	int data, ret;
+
+	data = MEAS_PD_EN | MEAS_TSIX_EN | MEAS_TSIY_EN
+		| MEAS_TSIZ1_EN | MEAS_TSIZ2_EN;
+	ret = pm860x_set_bits(touch->i2c, MEAS_EN3, data, data);
+	if (ret < 0)
+		goto out;
+	return 0;
+out:
+	return ret;
+}
+
+static void pm860x_touch_close(struct input_dev *dev)
+{
+	struct pm860x_touch *touch = input_get_drvdata(dev);
+	int data;
+
+	data = MEAS_PD_EN | MEAS_TSIX_EN | MEAS_TSIY_EN
+		| MEAS_TSIZ1_EN | MEAS_TSIZ2_EN;
+	pm860x_set_bits(touch->i2c, MEAS_EN3, data, 0);
+}
+
+#ifdef CONFIG_OF
+static int pm860x_touch_dt_init(struct platform_device *pdev,
+					  struct pm860x_chip *chip,
+					  int *res_x)
+{
+	struct i2c_client *i2c = (chip->id == CHIP_PM8607) ? chip->client \
+				 : chip->companion;
+	int data, n, ret;
+	if (!pdev->dev.parent->of_node)
+		return -ENODEV;
+
+	struct device_node *np __free(device_node) =
+		of_get_child_by_name(pdev->dev.parent->of_node, "touch");
+	if (!np) {
+		dev_err(&pdev->dev, "Can't find touch node\n");
+		return -EINVAL;
+	}
+	/* set GPADC MISC1 register */
+	data = 0;
+	if (!of_property_read_u32(np, "marvell,88pm860x-gpadc-prebias", &n))
+		data |= (n << 1) & PM8607_GPADC_PREBIAS_MASK;
+	if (!of_property_read_u32(np, "marvell,88pm860x-gpadc-slot-cycle", &n))
+		data |= (n << 3) & PM8607_GPADC_SLOT_CYCLE_MASK;
+	if (!of_property_read_u32(np, "marvell,88pm860x-gpadc-off-scale", &n))
+		data |= (n << 5) & PM8607_GPADC_OFF_SCALE_MASK;
+	if (!of_property_read_u32(np, "marvell,88pm860x-gpadc-sw-cal", &n))
+		data |= (n << 7) & PM8607_GPADC_SW_CAL_MASK;
+	if (data) {
+		ret = pm860x_reg_write(i2c, PM8607_GPADC_MISC1, data);
+		if (ret < 0)
+			return -EINVAL;
+	}
+	/* set tsi prebias time */
+	if (!of_property_read_u32(np, "marvell,88pm860x-tsi-prebias", &data)) {
+		ret = pm860x_reg_write(i2c, PM8607_TSI_PREBIAS, data);
+		if (ret < 0)
+			return -EINVAL;
+	}
+	/* set prebias & prechg time of pen detect */
+	data = 0;
+	if (!of_property_read_u32(np, "marvell,88pm860x-pen-prebias", &n))
+		data |= n & PM8607_PD_PREBIAS_MASK;
+	if (!of_property_read_u32(np, "marvell,88pm860x-pen-prechg", &n))
+		data |= n & PM8607_PD_PRECHG_MASK;
+	if (data) {
+		ret = pm860x_reg_write(i2c, PM8607_PD_PREBIAS, data);
+		if (ret < 0)
+			return -EINVAL;
+	}
+	of_property_read_u32(np, "marvell,88pm860x-resistor-X", res_x);
+
+	return 0;
+}
+#else
+#define pm860x_touch_dt_init(x, y, z)	(-1)
+#endif
+
+static int pm860x_touch_probe(struct platform_device *pdev)
+{
+	struct pm860x_chip *chip = dev_get_drvdata(pdev->dev.parent);
+	struct pm860x_touch_pdata *pdata = dev_get_platdata(&pdev->dev);
+	struct pm860x_touch *touch;
+	struct i2c_client *i2c = (chip->id == CHIP_PM8607) ? chip->client \
+				 : chip->companion;
+	int irq, ret, res_x = 0, data = 0;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return -EINVAL;
+
+	if (pm860x_touch_dt_init(pdev, chip, &res_x)) {
+		if (pdata) {
+			/* set GPADC MISC1 register */
+			data = 0;
+			data |= (pdata->gpadc_prebias << 1)
+				& PM8607_GPADC_PREBIAS_MASK;
+			data |= (pdata->slot_cycle << 3)
+				& PM8607_GPADC_SLOT_CYCLE_MASK;
+			data |= (pdata->off_scale << 5)
+				& PM8607_GPADC_OFF_SCALE_MASK;
+			data |= (pdata->sw_cal << 7)
+				& PM8607_GPADC_SW_CAL_MASK;
+			if (data) {
+				ret = pm860x_reg_write(i2c,
+					PM8607_GPADC_MISC1, data);
+				if (ret < 0)
+					return -EINVAL;
+			}
+			/* set tsi prebias time */
+			if (pdata->tsi_prebias) {
+				data = pdata->tsi_prebias;
+				ret = pm860x_reg_write(i2c,
+					PM8607_TSI_PREBIAS, data);
+				if (ret < 0)
+					return -EINVAL;
+			}
+			/* set prebias & prechg time of pen detect */
+			data = 0;
+			data |= pdata->pen_prebias
+				& PM8607_PD_PREBIAS_MASK;
+			data |= (pdata->pen_prechg << 5)
+				& PM8607_PD_PRECHG_MASK;
+			if (data) {
+				ret = pm860x_reg_write(i2c,
+					PM8607_PD_PREBIAS, data);
+				if (ret < 0)
+					return -EINVAL;
+			}
+			res_x = pdata->res_x;
+		} else {
+			dev_err(&pdev->dev, "failed to get platform data\n");
+			return -EINVAL;
+		}
+	}
+	/* enable GPADC */
+	ret = pm860x_set_bits(i2c, PM8607_GPADC_MISC1, PM8607_GPADC_EN,
+			      PM8607_GPADC_EN);
+	if (ret)
+		return ret;
+
+	touch = devm_kzalloc(&pdev->dev, sizeof(struct pm860x_touch),
+			     GFP_KERNEL);
+	if (!touch)
+		return -ENOMEM;
+
+	touch->idev = devm_input_allocate_device(&pdev->dev);
+	if (!touch->idev) {
+		dev_err(&pdev->dev, "Failed to allocate input device!\n");
+		return -ENOMEM;
+	}
+
+	touch->idev->name = "88pm860x-touch";
+	touch->idev->phys = "88pm860x/input0";
+	touch->idev->id.bustype = BUS_I2C;
+	touch->idev->dev.parent = &pdev->dev;
+	touch->idev->open = pm860x_touch_open;
+	touch->idev->close = pm860x_touch_close;
+	touch->chip = chip;
+	touch->i2c = i2c;
+	touch->irq = irq;
+	touch->res_x = res_x;
+	input_set_drvdata(touch->idev, touch);
+
+	ret = devm_request_threaded_irq(&pdev->dev, touch->irq, NULL,
+					pm860x_touch_handler, IRQF_ONESHOT,
+					"touch", touch);
+	if (ret < 0)
+		return ret;
+
+	__set_bit(EV_ABS, touch->idev->evbit);
+	__set_bit(ABS_X, touch->idev->absbit);
+	__set_bit(ABS_Y, touch->idev->absbit);
+	__set_bit(ABS_PRESSURE, touch->idev->absbit);
+	__set_bit(EV_SYN, touch->idev->evbit);
+	__set_bit(EV_KEY, touch->idev->evbit);
+	__set_bit(BTN_TOUCH, touch->idev->keybit);
+
+	input_set_abs_params(touch->idev, ABS_X, 0, 1 << ACCURATE_BIT, 0, 0);
+	input_set_abs_params(touch->idev, ABS_Y, 0, 1 << ACCURATE_BIT, 0, 0);
+	input_set_abs_params(touch->idev, ABS_PRESSURE, 0, 1 << ACCURATE_BIT,
+				0, 0);
+
+	ret = input_register_device(touch->idev);
+	if (ret < 0) {
+		dev_err(chip->dev, "Failed to register touch!\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static struct platform_driver pm860x_touch_driver = {
+	.driver	= {
+		.name	= "88pm860x-touch",
+	},
+	.probe	= pm860x_touch_probe,
+};
+module_platform_driver(pm860x_touch_driver);
+
+MODULE_DESCRIPTION("Touchscreen driver for Marvell Semiconductor 88PM860x");
+MODULE_AUTHOR("Haojian Zhuang <haojian.zhuang@marvell.com>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:88pm860x-touch");
+