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, 195 insertions, 0 deletions

diff --git a/drivers/gpu/host1x/mipi.c b/drivers/gpu/host1x/mipi.c
new file mode 100644
index 000000000..988681423
--- /dev/null
+++ b/drivers/gpu/host1x/mipi.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2013 NVIDIA Corporation
+ * Copyright (C) 2025 Svyatoslav Ryhel <clamor95@gmail.com>
+ */
+
+#include <linux/clk.h>
+#include <linux/io.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/tegra-mipi-cal.h>
+
+/* only need to support one provider */
+static struct {
+	struct device_node *np;
+	const struct tegra_mipi_ops *ops;
+} provider;
+
+/**
+ * tegra_mipi_enable - Enable the Tegra MIPI calibration device.
+ * @device: Handle to the Tegra MIPI calibration device.
+ *
+ * This calls the enable sequence for the Tegra MIPI calibration device.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int tegra_mipi_enable(struct tegra_mipi_device *device)
+{
+	if (device->ops->enable)
+		return device->ops->enable(device);
+
+	return 0;
+}
+EXPORT_SYMBOL(tegra_mipi_enable);
+
+/**
+ * tegra_mipi_disable - Disable the Tegra MIPI calibration device.
+ * @device: Handle to the Tegra MIPI calibration device.
+ *
+ * This calls the disable sequence for the Tegra MIPI calibration device.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int tegra_mipi_disable(struct tegra_mipi_device *device)
+{
+	if (device->ops->disable)
+		return device->ops->disable(device);
+
+	return 0;
+}
+EXPORT_SYMBOL(tegra_mipi_disable);
+
+/**
+ * tegra_mipi_start_calibration - Start the Tegra MIPI calibration sequence.
+ * @device: Handle to the Tegra MIPI calibration device.
+ *
+ * This initiates the calibration of CSI/DSI interfaces via the Tegra MIPI
+ * calibration device.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int tegra_mipi_start_calibration(struct tegra_mipi_device *device)
+{
+	if (device->ops->start_calibration)
+		return device->ops->start_calibration(device);
+
+	return 0;
+}
+EXPORT_SYMBOL(tegra_mipi_start_calibration);
+
+/**
+ * tegra_mipi_finish_calibration - Finish the Tegra MIPI calibration sequence.
+ * @device: Handle to the Tegra MIPI calibration device.
+ *
+ * This completes the calibration of CSI/DSI interfaces via the Tegra MIPI
+ * calibration device.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int tegra_mipi_finish_calibration(struct tegra_mipi_device *device)
+{
+	if (device->ops->finish_calibration)
+		return device->ops->finish_calibration(device);
+
+	return 0;
+}
+EXPORT_SYMBOL(tegra_mipi_finish_calibration);
+
+/**
+ * tegra_mipi_request - Request a Tegra MIPI calibration device.
+ * @device: Handle of the device requesting the MIPI calibration function.
+ * @np: Device node pointer of the device requesting the MIPI calibration
+ *	function.
+ *
+ * This function requests a reference to a Tegra MIPI calibration device.
+ *
+ * Returns a pointer to the Tegra MIPI calibration device on success,
+ * or an ERR_PTR-encoded error code on failure.
+ */
+struct tegra_mipi_device *tegra_mipi_request(struct device *device,
+					     struct device_node *np)
+{
+	struct tegra_mipi_device *mipidev;
+	struct of_phandle_args args;
+	int err;
+
+	err = of_parse_phandle_with_args(np, "nvidia,mipi-calibrate",
+					 "#nvidia,mipi-calibrate-cells", 0,
+					 &args);
+	if (err < 0)
+		return ERR_PTR(err);
+
+	if (provider.np != args.np) {
+		err = -ENODEV;
+		goto out;
+	}
+
+	mipidev = kzalloc_obj(*mipidev);
+	if (!mipidev) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	mipidev->pdev = of_find_device_by_node(args.np);
+	if (!mipidev->pdev) {
+		err = -ENODEV;
+		goto free;
+	}
+
+	of_node_put(args.np);
+
+	mipidev->ops = provider.ops;
+	mipidev->pads = args.args[0];
+
+	return mipidev;
+
+free:
+	kfree(mipidev);
+out:
+	of_node_put(args.np);
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL(tegra_mipi_request);
+
+/**
+ * tegra_mipi_free - Free a Tegra MIPI calibration device.
+ * @mipidev: Handle to the Tegra MIPI calibration device.
+ *
+ * This function releases a reference to a Tegra MIPI calibration device
+ * previously requested by tegra_mipi_request().
+ */
+void tegra_mipi_free(struct tegra_mipi_device *mipidev)
+{
+	platform_device_put(mipidev->pdev);
+	kfree(mipidev);
+}
+EXPORT_SYMBOL(tegra_mipi_free);
+
+static void tegra_mipi_remove_provider(void *data)
+{
+	provider.np = NULL;
+	provider.ops = NULL;
+}
+
+/**
+ * devm_tegra_mipi_add_provider - Managed registration of a Tegra MIPI
+ *				  calibration function provider.
+ * @device: Handle to the device providing the MIPI calibration function.
+ * @np: Device node pointer of the device providing the MIPI calibration
+ *	function.
+ * @ops: Operations supported by the MIPI calibration device.
+ *
+ * This registers a device that provides MIPI calibration functions.
+ * For Tegra20 and Tegra30, this is the CSI block, while Tegra114 and
+ * newer SoC generations have a dedicated hardware block for these
+ * functions.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int devm_tegra_mipi_add_provider(struct device *device, struct device_node *np,
+				 const struct tegra_mipi_ops *ops)
+{
+	if (provider.np)
+		return -EBUSY;
+
+	provider.np = np;
+	provider.ops = ops;
+
+	return devm_add_action_or_reset(device, tegra_mipi_remove_provider, NULL);
+}
+EXPORT_SYMBOL(devm_tegra_mipi_add_provider);