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, 249 insertions, 0 deletions

diff --git a/drivers/power/sequencing/pwrseq-thead-gpu.c b/drivers/power/sequencing/pwrseq-thead-gpu.c
new file mode 100644
index 000000000..a45318b4b
--- /dev/null
+++ b/drivers/power/sequencing/pwrseq-thead-gpu.c
@@ -0,0 +1,249 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * T-HEAD TH1520 GPU Power Sequencer Driver
+ *
+ * Copyright (c) 2025 Samsung Electronics Co., Ltd.
+ * Author: Michal Wilczynski <m.wilczynski@samsung.com>
+ *
+ * This driver implements the power sequence for the Imagination BXM-4-64
+ * GPU on the T-HEAD TH1520 SoC. The sequence requires coordinating resources
+ * from both the sequencer's parent device node (clkgen_reset) and the GPU's
+ * device node (clocks and core reset).
+ *
+ * The `match` function is used to acquire the GPU's resources when the
+ * GPU driver requests the "gpu-power" sequence target.
+ */
+
+#include <linux/auxiliary_bus.h>
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pwrseq/provider.h>
+#include <linux/reset.h>
+#include <linux/slab.h>
+
+#include <dt-bindings/power/thead,th1520-power.h>
+
+struct pwrseq_thead_gpu_ctx {
+	struct pwrseq_device *pwrseq;
+	struct reset_control *clkgen_reset;
+	struct device_node *aon_node;
+
+	/* Consumer resources */
+	struct device_node *consumer_node;
+	struct clk_bulk_data *clks;
+	int num_clks;
+	struct reset_control *gpu_reset;
+};
+
+static int pwrseq_thead_gpu_enable(struct pwrseq_device *pwrseq)
+{
+	struct pwrseq_thead_gpu_ctx *ctx = pwrseq_device_get_drvdata(pwrseq);
+	int ret;
+
+	if (!ctx->clks || !ctx->gpu_reset)
+		return -ENODEV;
+
+	ret = clk_bulk_prepare_enable(ctx->num_clks, ctx->clks);
+	if (ret)
+		return ret;
+
+	ret = reset_control_deassert(ctx->clkgen_reset);
+	if (ret)
+		goto err_disable_clks;
+
+	/*
+	 * According to the hardware manual, a delay of at least 32 clock
+	 * cycles is required between de-asserting the clkgen reset and
+	 * de-asserting the GPU reset. Assuming a worst-case scenario with
+	 * a very high GPU clock frequency, a delay of 1 microsecond is
+	 * sufficient to ensure this requirement is met across all
+	 * feasible GPU clock speeds.
+	 */
+	udelay(1);
+
+	ret = reset_control_deassert(ctx->gpu_reset);
+	if (ret)
+		goto err_assert_clkgen;
+
+	return 0;
+
+err_assert_clkgen:
+	reset_control_assert(ctx->clkgen_reset);
+err_disable_clks:
+	clk_bulk_disable_unprepare(ctx->num_clks, ctx->clks);
+	return ret;
+}
+
+static int pwrseq_thead_gpu_disable(struct pwrseq_device *pwrseq)
+{
+	struct pwrseq_thead_gpu_ctx *ctx = pwrseq_device_get_drvdata(pwrseq);
+	int ret = 0, err;
+
+	if (!ctx->clks || !ctx->gpu_reset)
+		return -ENODEV;
+
+	err = reset_control_assert(ctx->gpu_reset);
+	if (err)
+		ret = err;
+
+	err = reset_control_assert(ctx->clkgen_reset);
+	if (err && !ret)
+		ret = err;
+
+	clk_bulk_disable_unprepare(ctx->num_clks, ctx->clks);
+
+	/* ret stores values of the first error code */
+	return ret;
+}
+
+static const struct pwrseq_unit_data pwrseq_thead_gpu_unit = {
+	.name = "gpu-power-sequence",
+	.enable = pwrseq_thead_gpu_enable,
+	.disable = pwrseq_thead_gpu_disable,
+};
+
+static const struct pwrseq_target_data pwrseq_thead_gpu_target = {
+	.name = "gpu-power",
+	.unit = &pwrseq_thead_gpu_unit,
+};
+
+static const struct pwrseq_target_data *pwrseq_thead_gpu_targets[] = {
+	&pwrseq_thead_gpu_target,
+	NULL
+};
+
+static int pwrseq_thead_gpu_match(struct pwrseq_device *pwrseq,
+				  struct device *dev)
+{
+	struct pwrseq_thead_gpu_ctx *ctx = pwrseq_device_get_drvdata(pwrseq);
+	static const char *const clk_names[] = { "core", "sys" };
+	struct of_phandle_args pwr_spec;
+	int i, ret;
+
+	/* We only match the specific T-HEAD TH1520 GPU compatible */
+	if (!of_device_is_compatible(dev->of_node, "thead,th1520-gpu"))
+		return PWRSEQ_NO_MATCH;
+
+	ret = of_parse_phandle_with_args(dev->of_node, "power-domains",
+					 "#power-domain-cells", 0, &pwr_spec);
+	if (ret)
+		return PWRSEQ_NO_MATCH;
+
+	/* Additionally verify consumer device has AON as power-domain */
+	if (pwr_spec.np != ctx->aon_node || pwr_spec.args[0] != TH1520_GPU_PD) {
+		of_node_put(pwr_spec.np);
+		return PWRSEQ_NO_MATCH;
+	}
+
+	of_node_put(pwr_spec.np);
+
+	/* If a consumer is already bound, only allow a re-match from it */
+	if (ctx->consumer_node)
+		return ctx->consumer_node == dev->of_node ?
+				PWRSEQ_MATCH_OK : PWRSEQ_NO_MATCH;
+
+	ctx->num_clks = ARRAY_SIZE(clk_names);
+	ctx->clks = kzalloc_objs(*ctx->clks, ctx->num_clks);
+	if (!ctx->clks)
+		return -ENOMEM;
+
+	for (i = 0; i < ctx->num_clks; i++)
+		ctx->clks[i].id = clk_names[i];
+
+	ret = clk_bulk_get(dev, ctx->num_clks, ctx->clks);
+	if (ret)
+		goto err_free_clks;
+
+	ctx->gpu_reset = reset_control_get_shared(dev, NULL);
+	if (IS_ERR(ctx->gpu_reset)) {
+		ret = PTR_ERR(ctx->gpu_reset);
+		goto err_put_clks;
+	}
+
+	ctx->consumer_node = of_node_get(dev->of_node);
+
+	return PWRSEQ_MATCH_OK;
+
+err_put_clks:
+	clk_bulk_put(ctx->num_clks, ctx->clks);
+err_free_clks:
+	kfree(ctx->clks);
+	ctx->clks = NULL;
+
+	return ret;
+}
+
+static int pwrseq_thead_gpu_probe(struct auxiliary_device *adev,
+				  const struct auxiliary_device_id *id)
+{
+	struct device *dev = &adev->dev;
+	struct device *parent_dev = dev->parent;
+	struct pwrseq_thead_gpu_ctx *ctx;
+	struct pwrseq_config config = {};
+
+	ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->aon_node = parent_dev->of_node;
+
+	ctx->clkgen_reset =
+		devm_reset_control_get_exclusive(parent_dev, "gpu-clkgen");
+	if (IS_ERR(ctx->clkgen_reset))
+		return dev_err_probe(
+			dev, PTR_ERR(ctx->clkgen_reset),
+			"Failed to get GPU clkgen reset from parent\n");
+
+	config.parent = dev;
+	config.owner = THIS_MODULE;
+	config.drvdata = ctx;
+	config.match = pwrseq_thead_gpu_match;
+	config.targets = pwrseq_thead_gpu_targets;
+
+	ctx->pwrseq = devm_pwrseq_device_register(dev, &config);
+	if (IS_ERR(ctx->pwrseq))
+		return dev_err_probe(dev, PTR_ERR(ctx->pwrseq),
+				     "Failed to register power sequencer\n");
+
+	auxiliary_set_drvdata(adev, ctx);
+
+	return 0;
+}
+
+static void pwrseq_thead_gpu_remove(struct auxiliary_device *adev)
+{
+	struct pwrseq_thead_gpu_ctx *ctx = auxiliary_get_drvdata(adev);
+
+	if (ctx->gpu_reset)
+		reset_control_put(ctx->gpu_reset);
+
+	if (ctx->clks) {
+		clk_bulk_put(ctx->num_clks, ctx->clks);
+		kfree(ctx->clks);
+	}
+
+	if (ctx->consumer_node)
+		of_node_put(ctx->consumer_node);
+}
+
+static const struct auxiliary_device_id pwrseq_thead_gpu_id_table[] = {
+	{ .name = "th1520_pm_domains.pwrseq-gpu" },
+	{},
+};
+MODULE_DEVICE_TABLE(auxiliary, pwrseq_thead_gpu_id_table);
+
+static struct auxiliary_driver pwrseq_thead_gpu_driver = {
+	.driver = {
+		.name = "pwrseq-thead-gpu",
+	},
+	.probe = pwrseq_thead_gpu_probe,
+	.remove = pwrseq_thead_gpu_remove,
+	.id_table = pwrseq_thead_gpu_id_table,
+};
+module_auxiliary_driver(pwrseq_thead_gpu_driver);
+
+MODULE_AUTHOR("Michal Wilczynski <m.wilczynski@samsung.com>");
+MODULE_DESCRIPTION("T-HEAD TH1520 GPU power sequencer driver");
+MODULE_LICENSE("GPL");