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, 278 insertions, 0 deletions

diff --git a/drivers/base/regmap/regmap-sdw-mbq.c b/drivers/base/regmap/regmap-sdw-mbq.c
new file mode 100644
index 000000000..b0312f57c
--- /dev/null
+++ b/drivers/base/regmap/regmap-sdw-mbq.c
@@ -0,0 +1,278 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright(c) 2020 Intel Corporation.
+
+#include <linux/bits.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/soundwire/sdw.h>
+#include <linux/soundwire/sdw_registers.h>
+#include <sound/sdca_function.h>
+#include "internal.h"
+
+struct regmap_mbq_context {
+	struct device *dev;
+	struct sdw_slave *sdw;
+
+	bool (*readable_reg)(struct device *dev, unsigned int reg);
+
+	struct regmap_sdw_mbq_cfg cfg;
+
+	int val_size;
+};
+
+static int regmap_sdw_mbq_size(struct regmap_mbq_context *ctx, unsigned int reg)
+{
+	int size = ctx->val_size;
+
+	if (ctx->cfg.mbq_size) {
+		size = ctx->cfg.mbq_size(ctx->dev, reg);
+		if (!size || size > ctx->val_size)
+			return -EINVAL;
+	}
+
+	return size;
+}
+
+static bool regmap_sdw_mbq_deferrable(struct regmap_mbq_context *ctx, unsigned int reg)
+{
+	if (ctx->cfg.deferrable)
+		return ctx->cfg.deferrable(ctx->dev, reg);
+
+	return false;
+}
+
+static int regmap_sdw_mbq_poll_busy(struct sdw_slave *slave, unsigned int reg,
+				    struct regmap_mbq_context *ctx)
+{
+	struct device *dev = ctx->dev;
+	int val, ret = 0;
+
+	dev_dbg(dev, "Deferring transaction for 0x%x\n", reg);
+
+	reg = SDW_SDCA_CTL(SDW_SDCA_CTL_FUNC(reg), 0,
+			   SDCA_CTL_ENTITY_0_FUNCTION_STATUS, 0);
+
+	if (!ctx->readable_reg || ctx->readable_reg(dev, reg)) {
+		ret = read_poll_timeout(sdw_read_no_pm, val,
+					val < 0 || !(val & SDCA_CTL_ENTITY_0_FUNCTION_BUSY),
+					ctx->cfg.retry_us, ctx->cfg.timeout_us,
+					false, slave, reg);
+		if (val < 0)
+			return val;
+		if (ret)
+			dev_err(dev, "Function busy timed out 0x%x: %d\n", reg, val);
+	} else {
+		fsleep(ctx->cfg.timeout_us);
+	}
+
+	return ret;
+}
+
+static int regmap_sdw_mbq_write_impl(struct sdw_slave *slave,
+				     unsigned int reg, unsigned int val,
+				     int mbq_size)
+{
+	int shift = mbq_size * BITS_PER_BYTE;
+	int ret;
+
+	while (--mbq_size > 0) {
+		shift -= BITS_PER_BYTE;
+
+		ret = sdw_write_no_pm(slave, SDW_SDCA_MBQ_CTL(reg),
+				      (val >> shift) & 0xff);
+		if (ret < 0)
+			return ret;
+	}
+
+	return sdw_write_no_pm(slave, reg, val & 0xff);
+}
+
+static int regmap_sdw_mbq_write(void *context, unsigned int reg, unsigned int val)
+{
+	struct regmap_mbq_context *ctx = context;
+	struct sdw_slave *slave = ctx->sdw;
+	struct device *dev = ctx->dev;
+	bool deferrable = regmap_sdw_mbq_deferrable(ctx, reg);
+	int mbq_size = regmap_sdw_mbq_size(ctx, reg);
+	int ret;
+
+	if (mbq_size < 0)
+		return mbq_size;
+
+	/*
+	 * Technically the spec does allow a device to set itself to busy for
+	 * internal reasons, but since it doesn't provide any information on
+	 * how to handle timeouts in that case, for now the code will only
+	 * process a single wait/timeout on function busy and a single retry
+	 * of the transaction.
+	 */
+	ret = regmap_sdw_mbq_write_impl(slave, reg, val, mbq_size);
+	if (ret == -ENODATA) {
+		if (!deferrable)
+			dev_warn(dev, "Defer on undeferrable control: %x\n", reg);
+
+		ret = regmap_sdw_mbq_poll_busy(slave, reg, ctx);
+		if (ret)
+			return ret;
+
+		ret = regmap_sdw_mbq_write_impl(slave, reg, val, mbq_size);
+	}
+
+	return ret;
+}
+
+static int regmap_sdw_mbq_read_impl(struct sdw_slave *slave,
+				    unsigned int reg, unsigned int *val,
+				    int mbq_size)
+{
+	int shift = BITS_PER_BYTE;
+	int read;
+
+	read = sdw_read_no_pm(slave, reg);
+	if (read < 0)
+		return read;
+
+	*val = read;
+
+	while (--mbq_size > 0) {
+		read = sdw_read_no_pm(slave, SDW_SDCA_MBQ_CTL(reg));
+		if (read < 0)
+			return read;
+
+		*val |= read << shift;
+		shift += BITS_PER_BYTE;
+	}
+
+	return 0;
+}
+
+static int regmap_sdw_mbq_read(void *context, unsigned int reg, unsigned int *val)
+{
+	struct regmap_mbq_context *ctx = context;
+	struct sdw_slave *slave = ctx->sdw;
+	struct device *dev = ctx->dev;
+	bool deferrable = regmap_sdw_mbq_deferrable(ctx, reg);
+	int mbq_size = regmap_sdw_mbq_size(ctx, reg);
+	int ret;
+
+	if (mbq_size < 0)
+		return mbq_size;
+
+	/*
+	 * Technically the spec does allow a device to set itself to busy for
+	 * internal reasons, but since it doesn't provide any information on
+	 * how to handle timeouts in that case, for now the code will only
+	 * process a single wait/timeout on function busy and a single retry
+	 * of the transaction.
+	 */
+	ret = regmap_sdw_mbq_read_impl(slave, reg, val, mbq_size);
+	if (ret == -ENODATA) {
+		if (!deferrable)
+			dev_warn(dev, "Defer on undeferrable control: %x\n", reg);
+
+		ret = regmap_sdw_mbq_poll_busy(slave, reg, ctx);
+		if (ret)
+			return ret;
+
+		ret = regmap_sdw_mbq_read_impl(slave, reg, val, mbq_size);
+	}
+
+	return ret;
+}
+
+static const struct regmap_bus regmap_sdw_mbq = {
+	.reg_read = regmap_sdw_mbq_read,
+	.reg_write = regmap_sdw_mbq_write,
+	.reg_format_endian_default = REGMAP_ENDIAN_LITTLE,
+	.val_format_endian_default = REGMAP_ENDIAN_LITTLE,
+};
+
+static int regmap_sdw_mbq_config_check(const struct regmap_config *config)
+{
+	if (config->val_bits > (sizeof(unsigned int) * BITS_PER_BYTE))
+		return -ENOTSUPP;
+
+	/* Registers are 32 bits wide */
+	if (config->reg_bits != 32)
+		return -ENOTSUPP;
+
+	if (config->pad_bits != 0)
+		return -ENOTSUPP;
+
+	return 0;
+}
+
+static struct regmap_mbq_context *
+regmap_sdw_mbq_gen_context(struct device *dev,
+			   struct sdw_slave *sdw,
+			   const struct regmap_config *config,
+			   const struct regmap_sdw_mbq_cfg *mbq_config)
+{
+	struct regmap_mbq_context *ctx;
+
+	ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+
+	ctx->dev = dev;
+	ctx->sdw = sdw;
+
+	if (mbq_config)
+		ctx->cfg = *mbq_config;
+
+	ctx->val_size = config->val_bits / BITS_PER_BYTE;
+	ctx->readable_reg = config->readable_reg;
+
+	return ctx;
+}
+
+struct regmap *__regmap_init_sdw_mbq(struct device *dev, struct sdw_slave *sdw,
+				     const struct regmap_config *config,
+				     const struct regmap_sdw_mbq_cfg *mbq_config,
+				     struct lock_class_key *lock_key,
+				     const char *lock_name)
+{
+	struct regmap_mbq_context *ctx;
+	int ret;
+
+	ret = regmap_sdw_mbq_config_check(config);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ctx = regmap_sdw_mbq_gen_context(dev, sdw, config, mbq_config);
+	if (IS_ERR(ctx))
+		return ERR_CAST(ctx);
+
+	return __regmap_init(dev, &regmap_sdw_mbq, ctx,
+			     config, lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__regmap_init_sdw_mbq);
+
+struct regmap *__devm_regmap_init_sdw_mbq(struct device *dev, struct sdw_slave *sdw,
+					  const struct regmap_config *config,
+					  const struct regmap_sdw_mbq_cfg *mbq_config,
+					  struct lock_class_key *lock_key,
+					  const char *lock_name)
+{
+	struct regmap_mbq_context *ctx;
+	int ret;
+
+	ret = regmap_sdw_mbq_config_check(config);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ctx = regmap_sdw_mbq_gen_context(dev, sdw, config, mbq_config);
+	if (IS_ERR(ctx))
+		return ERR_CAST(ctx);
+
+	return __devm_regmap_init(dev, &regmap_sdw_mbq, ctx,
+				  config, lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_sdw_mbq);
+
+MODULE_DESCRIPTION("regmap SoundWire MBQ Module");
+MODULE_LICENSE("GPL");