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, 188 insertions, 0 deletions

diff --git a/drivers/soundwire/master.c b/drivers/soundwire/master.c
new file mode 100644
index 000000000..440bfc52c
--- /dev/null
+++ b/drivers/soundwire/master.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright(c) 2019-2020 Intel Corporation.
+
+#include <linux/device.h>
+#include <linux/acpi.h>
+#include <linux/pm_runtime.h>
+#include <linux/soundwire/sdw.h>
+#include <linux/soundwire/sdw_type.h>
+#include "bus.h"
+
+/*
+ * The 3s value for autosuspend will only be used if there are no
+ * devices physically attached on a bus segment. In practice enabling
+ * the bus operation will result in children devices become active and
+ * the master device will only suspend when all its children are no
+ * longer active.
+ */
+#define SDW_MASTER_SUSPEND_DELAY_MS 3000
+
+/*
+ * The sysfs for properties reflects the MIPI description as given
+ * in the MIPI DisCo spec
+ *
+ * Base file is:
+ *	sdw-master-N
+ *      |---- revision
+ *      |---- clk_stop_modes
+ *      |---- max_clk_freq
+ *      |---- clk_freq
+ *      |---- clk_gears
+ *      |---- default_row
+ *      |---- default_col
+ *      |---- dynamic_shape
+ *      |---- err_threshold
+ */
+
+#define sdw_master_attr(field, format_string)				\
+static ssize_t field##_show(struct device *dev,				\
+			    struct device_attribute *attr,		\
+			    char *buf)					\
+{									\
+	struct sdw_master_device *md = dev_to_sdw_master_device(dev);	\
+	return sprintf(buf, format_string, md->bus->prop.field);	\
+}									\
+static DEVICE_ATTR_RO(field)
+
+sdw_master_attr(revision, "0x%x\n");
+sdw_master_attr(clk_stop_modes, "0x%x\n");
+sdw_master_attr(max_clk_freq, "%d\n");
+sdw_master_attr(default_row, "%d\n");
+sdw_master_attr(default_col, "%d\n");
+sdw_master_attr(default_frame_rate, "%d\n");
+sdw_master_attr(dynamic_frame, "%d\n");
+sdw_master_attr(err_threshold, "%d\n");
+
+static ssize_t clock_frequencies_show(struct device *dev,
+				      struct device_attribute *attr, char *buf)
+{
+	struct sdw_master_device *md = dev_to_sdw_master_device(dev);
+	ssize_t size = 0;
+	int i;
+
+	for (i = 0; i < md->bus->prop.num_clk_freq; i++)
+		size += sprintf(buf + size, "%8d ",
+				md->bus->prop.clk_freq[i]);
+	size += sprintf(buf + size, "\n");
+
+	return size;
+}
+static DEVICE_ATTR_RO(clock_frequencies);
+
+static ssize_t clock_gears_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct sdw_master_device *md = dev_to_sdw_master_device(dev);
+	ssize_t size = 0;
+	int i;
+
+	for (i = 0; i < md->bus->prop.num_clk_gears; i++)
+		size += sprintf(buf + size, "%8d ",
+				md->bus->prop.clk_gears[i]);
+	size += sprintf(buf + size, "\n");
+
+	return size;
+}
+static DEVICE_ATTR_RO(clock_gears);
+
+static struct attribute *master_node_attrs[] = {
+	&dev_attr_revision.attr,
+	&dev_attr_clk_stop_modes.attr,
+	&dev_attr_max_clk_freq.attr,
+	&dev_attr_default_row.attr,
+	&dev_attr_default_col.attr,
+	&dev_attr_default_frame_rate.attr,
+	&dev_attr_dynamic_frame.attr,
+	&dev_attr_err_threshold.attr,
+	&dev_attr_clock_frequencies.attr,
+	&dev_attr_clock_gears.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(master_node);
+
+static void sdw_master_device_release(struct device *dev)
+{
+	struct sdw_master_device *md = dev_to_sdw_master_device(dev);
+
+	kfree(md);
+}
+
+static const struct dev_pm_ops master_dev_pm = {
+	SET_RUNTIME_PM_OPS(pm_generic_runtime_suspend,
+			   pm_generic_runtime_resume, NULL)
+};
+
+const struct device_type sdw_master_type = {
+	.name =		"soundwire_master",
+	.release =	sdw_master_device_release,
+	.pm = &master_dev_pm,
+};
+
+/**
+ * sdw_master_device_add() - create a Linux Master Device representation.
+ * @bus: SDW bus instance
+ * @parent: parent device
+ * @fwnode: firmware node handle
+ */
+int sdw_master_device_add(struct sdw_bus *bus, struct device *parent,
+			  struct fwnode_handle *fwnode)
+{
+	struct sdw_master_device *md;
+	int ret;
+
+	if (!parent)
+		return -EINVAL;
+
+	md = kzalloc_obj(*md);
+	if (!md)
+		return -ENOMEM;
+
+	md->dev.bus = &sdw_bus_type;
+	md->dev.type = &sdw_master_type;
+	md->dev.parent = parent;
+	md->dev.groups = master_node_groups;
+	md->dev.of_node = parent->of_node;
+	md->dev.fwnode = fwnode;
+	md->dev.dma_mask = parent->dma_mask;
+
+	dev_set_name(&md->dev, "sdw-master-%d-%d", bus->controller_id, bus->link_id);
+
+	ret = device_register(&md->dev);
+	if (ret) {
+		dev_err(parent, "Failed to add master: ret %d\n", ret);
+		/*
+		 * On err, don't free but drop ref as this will be freed
+		 * when release method is invoked.
+		 */
+		put_device(&md->dev);
+		goto device_register_err;
+	}
+
+	/* add shortcuts to improve code readability/compactness */
+	md->bus = bus;
+	bus->dev = &md->dev;
+	bus->md = md;
+
+	pm_runtime_set_autosuspend_delay(&bus->md->dev, SDW_MASTER_SUSPEND_DELAY_MS);
+	pm_runtime_use_autosuspend(&bus->md->dev);
+	pm_runtime_mark_last_busy(&bus->md->dev);
+	pm_runtime_set_active(&bus->md->dev);
+	pm_runtime_enable(&bus->md->dev);
+	pm_runtime_idle(&bus->md->dev);
+device_register_err:
+	return ret;
+}
+
+/**
+ * sdw_master_device_del() - delete a Linux Master Device representation.
+ * @bus: bus handle
+ *
+ * This function is the dual of sdw_master_device_add()
+ */
+int sdw_master_device_del(struct sdw_bus *bus)
+{
+	pm_runtime_disable(&bus->md->dev);
+	device_unregister(bus->dev);
+
+	return 0;
+}