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, 284 insertions, 0 deletions

diff --git a/drivers/extcon/extcon-intel-mrfld.c b/drivers/extcon/extcon-intel-mrfld.c
new file mode 100644
index 000000000..7246d704f
--- /dev/null
+++ b/drivers/extcon/extcon-intel-mrfld.c
@@ -0,0 +1,284 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * extcon driver for Basin Cove PMIC
+ *
+ * Copyright (c) 2019, Intel Corporation.
+ * Author: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
+ */
+
+#include <linux/extcon-provider.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/intel_soc_pmic.h>
+#include <linux/mfd/intel_soc_pmic_mrfld.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#include "extcon-intel.h"
+
+#define BCOVE_USBIDCTRL			0x19
+#define BCOVE_USBIDCTRL_ID		BIT(0)
+#define BCOVE_USBIDCTRL_ACA		BIT(1)
+#define BCOVE_USBIDCTRL_ALL	(BCOVE_USBIDCTRL_ID | BCOVE_USBIDCTRL_ACA)
+
+#define BCOVE_USBIDSTS			0x1a
+#define BCOVE_USBIDSTS_GND		BIT(0)
+#define BCOVE_USBIDSTS_RARBRC_MASK	GENMASK(2, 1)
+#define BCOVE_USBIDSTS_RARBRC_SHIFT	1
+#define BCOVE_USBIDSTS_NO_ACA		0
+#define BCOVE_USBIDSTS_R_ID_A		1
+#define BCOVE_USBIDSTS_R_ID_B		2
+#define BCOVE_USBIDSTS_R_ID_C		3
+#define BCOVE_USBIDSTS_FLOAT		BIT(3)
+#define BCOVE_USBIDSTS_SHORT		BIT(4)
+
+#define BCOVE_CHGRIRQ_ALL	(BCOVE_CHGRIRQ_VBUSDET | BCOVE_CHGRIRQ_DCDET | \
+				 BCOVE_CHGRIRQ_BATTDET | BCOVE_CHGRIRQ_USBIDDET)
+
+#define BCOVE_CHGRCTRL0			0x4b
+#define BCOVE_CHGRCTRL0_CHGRRESET	BIT(0)
+#define BCOVE_CHGRCTRL0_EMRGCHREN	BIT(1)
+#define BCOVE_CHGRCTRL0_EXTCHRDIS	BIT(2)
+#define BCOVE_CHGRCTRL0_SWCONTROL	BIT(3)
+#define BCOVE_CHGRCTRL0_TTLCK		BIT(4)
+#define BCOVE_CHGRCTRL0_BIT_5		BIT(5)
+#define BCOVE_CHGRCTRL0_BIT_6		BIT(6)
+#define BCOVE_CHGRCTRL0_CHR_WDT_NOKICK	BIT(7)
+
+struct mrfld_extcon_data {
+	struct device *dev;
+	struct regmap *regmap;
+	struct extcon_dev *edev;
+	unsigned int status;
+	unsigned int id;
+};
+
+static const unsigned int mrfld_extcon_cable[] = {
+	EXTCON_USB,
+	EXTCON_USB_HOST,
+	EXTCON_CHG_USB_SDP,
+	EXTCON_CHG_USB_CDP,
+	EXTCON_CHG_USB_DCP,
+	EXTCON_CHG_USB_ACA,
+	EXTCON_NONE,
+};
+
+static int mrfld_extcon_clear(struct mrfld_extcon_data *data, unsigned int reg,
+			      unsigned int mask)
+{
+	return regmap_update_bits(data->regmap, reg, mask, 0x00);
+}
+
+static int mrfld_extcon_set(struct mrfld_extcon_data *data, unsigned int reg,
+			    unsigned int mask)
+{
+	return regmap_update_bits(data->regmap, reg, mask, 0xff);
+}
+
+static int mrfld_extcon_sw_control(struct mrfld_extcon_data *data, bool enable)
+{
+	unsigned int mask = BCOVE_CHGRCTRL0_SWCONTROL;
+	struct device *dev = data->dev;
+	int ret;
+
+	if (enable)
+		ret = mrfld_extcon_set(data, BCOVE_CHGRCTRL0, mask);
+	else
+		ret = mrfld_extcon_clear(data, BCOVE_CHGRCTRL0, mask);
+	if (ret)
+		dev_err(dev, "can't set SW control: %d\n", ret);
+	return ret;
+}
+
+static int mrfld_extcon_get_id(struct mrfld_extcon_data *data)
+{
+	struct regmap *regmap = data->regmap;
+	unsigned int id;
+	bool ground;
+	int ret;
+
+	ret = regmap_read(regmap, BCOVE_USBIDSTS, &id);
+	if (ret)
+		return ret;
+
+	if (id & BCOVE_USBIDSTS_FLOAT)
+		return INTEL_USB_ID_FLOAT;
+
+	switch ((id & BCOVE_USBIDSTS_RARBRC_MASK) >> BCOVE_USBIDSTS_RARBRC_SHIFT) {
+	case BCOVE_USBIDSTS_R_ID_A:
+		return INTEL_USB_RID_A;
+	case BCOVE_USBIDSTS_R_ID_B:
+		return INTEL_USB_RID_B;
+	case BCOVE_USBIDSTS_R_ID_C:
+		return INTEL_USB_RID_C;
+	}
+
+	/*
+	 * PMIC A0 reports USBIDSTS_GND = 1 for ID_GND,
+	 * but PMIC B0 reports USBIDSTS_GND = 0 for ID_GND.
+	 * Thus we must check this bit at last.
+	 */
+	ground = id & BCOVE_USBIDSTS_GND;
+	switch ('A' + BCOVE_MAJOR(data->id)) {
+	case 'A':
+		return ground ? INTEL_USB_ID_GND : INTEL_USB_ID_FLOAT;
+	case 'B':
+		return ground ? INTEL_USB_ID_FLOAT : INTEL_USB_ID_GND;
+	}
+
+	/* Unknown or unsupported type */
+	return INTEL_USB_ID_FLOAT;
+}
+
+static int mrfld_extcon_role_detect(struct mrfld_extcon_data *data)
+{
+	unsigned int id;
+	bool usb_host;
+	int ret;
+
+	ret = mrfld_extcon_get_id(data);
+	if (ret < 0)
+		return ret;
+
+	id = ret;
+
+	usb_host = (id == INTEL_USB_ID_GND) || (id == INTEL_USB_RID_A);
+	extcon_set_state_sync(data->edev, EXTCON_USB_HOST, usb_host);
+
+	return 0;
+}
+
+static int mrfld_extcon_cable_detect(struct mrfld_extcon_data *data)
+{
+	struct regmap *regmap = data->regmap;
+	unsigned int status, change;
+	int ret;
+
+	/*
+	 * It seems SCU firmware clears the content of BCOVE_CHGRIRQ1
+	 * and makes it useless for OS. Instead we compare a previously
+	 * stored status to the current one, provided by BCOVE_SCHGRIRQ1.
+	 */
+	ret = regmap_read(regmap, BCOVE_SCHGRIRQ1, &status);
+	if (ret)
+		return ret;
+
+	change = status ^ data->status;
+	if (!change)
+		return -ENODATA;
+
+	if (change & BCOVE_CHGRIRQ_USBIDDET) {
+		ret = mrfld_extcon_role_detect(data);
+		if (ret)
+			return ret;
+	}
+
+	data->status = status;
+
+	return 0;
+}
+
+static irqreturn_t mrfld_extcon_interrupt(int irq, void *dev_id)
+{
+	struct mrfld_extcon_data *data = dev_id;
+	int ret;
+
+	ret = mrfld_extcon_cable_detect(data);
+
+	mrfld_extcon_clear(data, BCOVE_MIRQLVL1, BCOVE_LVL1_CHGR);
+
+	return ret ? IRQ_NONE: IRQ_HANDLED;
+}
+
+static int mrfld_extcon_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct intel_soc_pmic *pmic = dev_get_drvdata(dev->parent);
+	struct regmap *regmap = pmic->regmap;
+	struct mrfld_extcon_data *data;
+	unsigned int status;
+	unsigned int id;
+	int irq, ret;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->dev = dev;
+	data->regmap = regmap;
+
+	data->edev = devm_extcon_dev_allocate(dev, mrfld_extcon_cable);
+	if (IS_ERR(data->edev))
+		return PTR_ERR(data->edev);
+
+	ret = devm_extcon_dev_register(dev, data->edev);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "can't register extcon device\n");
+
+	ret = devm_request_threaded_irq(dev, irq, NULL, mrfld_extcon_interrupt,
+					IRQF_ONESHOT | IRQF_SHARED, pdev->name,
+					data);
+	if (ret)
+		return dev_err_probe(dev, ret, "can't register IRQ handler\n");
+
+	ret = regmap_read(regmap, BCOVE_ID, &id);
+	if (ret)
+		return dev_err_probe(dev, ret, "can't read PMIC ID\n");
+
+	data->id = id;
+
+	ret = mrfld_extcon_sw_control(data, true);
+	if (ret)
+		return ret;
+
+	/* Get initial state */
+	mrfld_extcon_role_detect(data);
+
+	/*
+	 * Cached status value is used for cable detection, see comments
+	 * in mrfld_extcon_cable_detect(), we need to sync cached value
+	 * with a real state of the hardware.
+	 */
+	regmap_read(regmap, BCOVE_SCHGRIRQ1, &status);
+	data->status = status;
+
+	mrfld_extcon_clear(data, BCOVE_MIRQLVL1, BCOVE_LVL1_CHGR);
+	mrfld_extcon_clear(data, BCOVE_MCHGRIRQ1, BCOVE_CHGRIRQ_ALL);
+
+	mrfld_extcon_set(data, BCOVE_USBIDCTRL, BCOVE_USBIDCTRL_ALL);
+
+	platform_set_drvdata(pdev, data);
+
+	return 0;
+}
+
+static void mrfld_extcon_remove(struct platform_device *pdev)
+{
+	struct mrfld_extcon_data *data = platform_get_drvdata(pdev);
+
+	mrfld_extcon_sw_control(data, false);
+}
+
+static const struct platform_device_id mrfld_extcon_id_table[] = {
+	{ .name = "mrfld_bcove_pwrsrc" },
+	{}
+};
+MODULE_DEVICE_TABLE(platform, mrfld_extcon_id_table);
+
+static struct platform_driver mrfld_extcon_driver = {
+	.driver = {
+		.name	= "mrfld_bcove_pwrsrc",
+	},
+	.probe		= mrfld_extcon_probe,
+	.remove		= mrfld_extcon_remove,
+	.id_table	= mrfld_extcon_id_table,
+};
+module_platform_driver(mrfld_extcon_driver);
+
+MODULE_AUTHOR("Andy Shevchenko <andriy.shevchenko@linux.intel.com>");
+MODULE_DESCRIPTION("extcon driver for Intel Merrifield Basin Cove PMIC");
+MODULE_LICENSE("GPL v2");