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, 222 insertions, 0 deletions

diff --git a/drivers/nvmem/lan9662-otpc.c b/drivers/nvmem/lan9662-otpc.c
new file mode 100644
index 000000000..56fc19f09
--- /dev/null
+++ b/drivers/nvmem/lan9662-otpc.c
@@ -0,0 +1,222 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+#define OTP_OTP_PWR_DN(t)			(t + 0x00)
+#define OTP_OTP_PWR_DN_OTP_PWRDN_N		BIT(0)
+#define OTP_OTP_ADDR_HI(t)			(t + 0x04)
+#define OTP_OTP_ADDR_LO(t)			(t + 0x08)
+#define OTP_OTP_PRGM_DATA(t)			(t + 0x10)
+#define OTP_OTP_PRGM_MODE(t)			(t + 0x14)
+#define OTP_OTP_PRGM_MODE_OTP_PGM_MODE_BYTE	BIT(0)
+#define OTP_OTP_RD_DATA(t)			(t + 0x18)
+#define OTP_OTP_FUNC_CMD(t)			(t + 0x20)
+#define OTP_OTP_FUNC_CMD_OTP_PROGRAM		BIT(1)
+#define OTP_OTP_FUNC_CMD_OTP_READ		BIT(0)
+#define OTP_OTP_CMD_GO(t)			(t + 0x28)
+#define OTP_OTP_CMD_GO_OTP_GO			BIT(0)
+#define OTP_OTP_PASS_FAIL(t)			(t + 0x2c)
+#define OTP_OTP_PASS_FAIL_OTP_READ_PROHIBITED	BIT(3)
+#define OTP_OTP_PASS_FAIL_OTP_WRITE_PROHIBITED	BIT(2)
+#define OTP_OTP_PASS_FAIL_OTP_FAIL		BIT(0)
+#define OTP_OTP_STATUS(t)			(t + 0x30)
+#define OTP_OTP_STATUS_OTP_CPUMPEN		BIT(1)
+#define OTP_OTP_STATUS_OTP_BUSY			BIT(0)
+
+#define OTP_MEM_SIZE 8192
+#define OTP_SLEEP_US 10
+#define OTP_TIMEOUT_US 500000
+
+struct lan9662_otp {
+	struct device *dev;
+	void __iomem *base;
+};
+
+static int lan9662_otp_wait_flag_clear(void __iomem *reg, u32 flag)
+{
+	u32 val;
+
+	return readl_poll_timeout(reg, val, !(val & flag),
+				  OTP_SLEEP_US, OTP_TIMEOUT_US);
+}
+
+static int lan9662_otp_power(struct lan9662_otp *otp, bool up)
+{
+	void __iomem *pwrdn = OTP_OTP_PWR_DN(otp->base);
+
+	if (up) {
+		writel(readl(pwrdn) & ~OTP_OTP_PWR_DN_OTP_PWRDN_N, pwrdn);
+		if (lan9662_otp_wait_flag_clear(OTP_OTP_STATUS(otp->base),
+						OTP_OTP_STATUS_OTP_CPUMPEN))
+			return -ETIMEDOUT;
+	} else {
+		writel(readl(pwrdn) | OTP_OTP_PWR_DN_OTP_PWRDN_N, pwrdn);
+	}
+
+	return 0;
+}
+
+static int lan9662_otp_execute(struct lan9662_otp *otp)
+{
+	if (lan9662_otp_wait_flag_clear(OTP_OTP_CMD_GO(otp->base),
+					OTP_OTP_CMD_GO_OTP_GO))
+		return -ETIMEDOUT;
+
+	if (lan9662_otp_wait_flag_clear(OTP_OTP_STATUS(otp->base),
+					OTP_OTP_STATUS_OTP_BUSY))
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static void lan9662_otp_set_address(struct lan9662_otp *otp, u32 offset)
+{
+	writel(0xff & (offset >> 8), OTP_OTP_ADDR_HI(otp->base));
+	writel(0xff & offset, OTP_OTP_ADDR_LO(otp->base));
+}
+
+static int lan9662_otp_read_byte(struct lan9662_otp *otp, u32 offset, u8 *dst)
+{
+	u32 pass;
+	int rc;
+
+	lan9662_otp_set_address(otp, offset);
+	writel(OTP_OTP_FUNC_CMD_OTP_READ, OTP_OTP_FUNC_CMD(otp->base));
+	writel(OTP_OTP_CMD_GO_OTP_GO, OTP_OTP_CMD_GO(otp->base));
+	rc = lan9662_otp_execute(otp);
+	if (!rc) {
+		pass = readl(OTP_OTP_PASS_FAIL(otp->base));
+		if (pass & OTP_OTP_PASS_FAIL_OTP_READ_PROHIBITED)
+			return -EACCES;
+		*dst = (u8) readl(OTP_OTP_RD_DATA(otp->base));
+	}
+	return rc;
+}
+
+static int lan9662_otp_write_byte(struct lan9662_otp *otp, u32 offset, u8 data)
+{
+	u32 pass;
+	int rc;
+
+	lan9662_otp_set_address(otp, offset);
+	writel(OTP_OTP_PRGM_MODE_OTP_PGM_MODE_BYTE, OTP_OTP_PRGM_MODE(otp->base));
+	writel(data, OTP_OTP_PRGM_DATA(otp->base));
+	writel(OTP_OTP_FUNC_CMD_OTP_PROGRAM, OTP_OTP_FUNC_CMD(otp->base));
+	writel(OTP_OTP_CMD_GO_OTP_GO, OTP_OTP_CMD_GO(otp->base));
+
+	rc = lan9662_otp_execute(otp);
+	if (!rc) {
+		pass = readl(OTP_OTP_PASS_FAIL(otp->base));
+		if (pass & OTP_OTP_PASS_FAIL_OTP_WRITE_PROHIBITED)
+			return -EACCES;
+		if (pass & OTP_OTP_PASS_FAIL_OTP_FAIL)
+			return -EIO;
+	}
+	return rc;
+}
+
+static int lan9662_otp_read(void *context, unsigned int offset,
+			    void *_val, size_t bytes)
+{
+	struct lan9662_otp *otp = context;
+	u8 *val = _val;
+	uint8_t data;
+	int i, rc = 0;
+
+	lan9662_otp_power(otp, true);
+	for (i = 0; i < bytes; i++) {
+		rc = lan9662_otp_read_byte(otp, offset + i, &data);
+		if (rc < 0)
+			break;
+		*val++ = data;
+	}
+	lan9662_otp_power(otp, false);
+
+	return rc;
+}
+
+static int lan9662_otp_write(void *context, unsigned int offset,
+			     void *_val, size_t bytes)
+{
+	struct lan9662_otp *otp = context;
+	u8 *val = _val;
+	u8 data, newdata;
+	int i, rc = 0;
+
+	lan9662_otp_power(otp, true);
+	for (i = 0; i < bytes; i++) {
+		/* Skip zero bytes */
+		if (val[i]) {
+			rc = lan9662_otp_read_byte(otp, offset + i, &data);
+			if (rc < 0)
+				break;
+
+			newdata = data | val[i];
+			if (newdata == data)
+				continue;
+
+			rc = lan9662_otp_write_byte(otp, offset + i,
+						      newdata);
+			if (rc < 0)
+				break;
+		}
+	}
+	lan9662_otp_power(otp, false);
+
+	return rc;
+}
+
+static struct nvmem_config otp_config = {
+	.name = "lan9662-otp",
+	.stride = 1,
+	.word_size = 1,
+	.reg_read = lan9662_otp_read,
+	.reg_write = lan9662_otp_write,
+	.size = OTP_MEM_SIZE,
+};
+
+static int lan9662_otp_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct nvmem_device *nvmem;
+	struct lan9662_otp *otp;
+
+	otp = devm_kzalloc(&pdev->dev, sizeof(*otp), GFP_KERNEL);
+	if (!otp)
+		return -ENOMEM;
+
+	otp->dev = dev;
+	otp->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(otp->base))
+		return PTR_ERR(otp->base);
+
+	otp_config.priv = otp;
+	otp_config.dev = dev;
+
+	nvmem = devm_nvmem_register(dev, &otp_config);
+
+	return PTR_ERR_OR_ZERO(nvmem);
+}
+
+static const struct of_device_id lan9662_otp_match[] = {
+	{ .compatible = "microchip,lan9662-otpc", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, lan9662_otp_match);
+
+static struct platform_driver lan9662_otp_driver = {
+	.probe = lan9662_otp_probe,
+	.driver = {
+		.name = "lan9662-otp",
+		.of_match_table = lan9662_otp_match,
+	},
+};
+module_platform_driver(lan9662_otp_driver);
+
+MODULE_AUTHOR("Horatiu Vultur <horatiu.vultur@microchip.com>");
+MODULE_DESCRIPTION("lan9662 OTP driver");
+MODULE_LICENSE("GPL");