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, 214 insertions, 0 deletions

diff --git a/drivers/gpu/ipu-v3/ipu-dmfc.c b/drivers/gpu/ipu-v3/ipu-dmfc.c
new file mode 100644
index 000000000..ae682084a
--- /dev/null
+++ b/drivers/gpu/ipu-v3/ipu-dmfc.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2010 Sascha Hauer <s.hauer@pengutronix.de>
+ * Copyright (C) 2005-2009 Freescale Semiconductor, Inc.
+ */
+#include <linux/export.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+
+#include <video/imx-ipu-v3.h>
+#include "ipu-prv.h"
+
+#define DMFC_RD_CHAN		0x0000
+#define DMFC_WR_CHAN		0x0004
+#define DMFC_WR_CHAN_DEF	0x0008
+#define DMFC_DP_CHAN		0x000c
+#define DMFC_DP_CHAN_DEF	0x0010
+#define DMFC_GENERAL1		0x0014
+#define DMFC_GENERAL2		0x0018
+#define DMFC_IC_CTRL		0x001c
+#define DMFC_WR_CHAN_ALT	0x0020
+#define DMFC_WR_CHAN_DEF_ALT	0x0024
+#define DMFC_DP_CHAN_ALT	0x0028
+#define DMFC_DP_CHAN_DEF_ALT	0x002c
+#define DMFC_GENERAL1_ALT	0x0030
+#define DMFC_STAT		0x0034
+
+#define DMFC_WR_CHAN_1_28		0
+#define DMFC_WR_CHAN_2_41		8
+#define DMFC_WR_CHAN_1C_42		16
+#define DMFC_WR_CHAN_2C_43		24
+
+#define DMFC_DP_CHAN_5B_23		0
+#define DMFC_DP_CHAN_5F_27		8
+#define DMFC_DP_CHAN_6B_24		16
+#define DMFC_DP_CHAN_6F_29		24
+
+struct dmfc_channel_data {
+	int		ipu_channel;
+	unsigned long	channel_reg;
+	unsigned long	shift;
+	unsigned	eot_shift;
+	unsigned	max_fifo_lines;
+};
+
+static const struct dmfc_channel_data dmfcdata[] = {
+	{
+		.ipu_channel	= IPUV3_CHANNEL_MEM_BG_SYNC,
+		.channel_reg	= DMFC_DP_CHAN,
+		.shift		= DMFC_DP_CHAN_5B_23,
+		.eot_shift	= 20,
+		.max_fifo_lines	= 3,
+	}, {
+		.ipu_channel	= 24,
+		.channel_reg	= DMFC_DP_CHAN,
+		.shift		= DMFC_DP_CHAN_6B_24,
+		.eot_shift	= 22,
+		.max_fifo_lines	= 1,
+	}, {
+		.ipu_channel	= IPUV3_CHANNEL_MEM_FG_SYNC,
+		.channel_reg	= DMFC_DP_CHAN,
+		.shift		= DMFC_DP_CHAN_5F_27,
+		.eot_shift	= 21,
+		.max_fifo_lines	= 2,
+	}, {
+		.ipu_channel	= IPUV3_CHANNEL_MEM_DC_SYNC,
+		.channel_reg	= DMFC_WR_CHAN,
+		.shift		= DMFC_WR_CHAN_1_28,
+		.eot_shift	= 16,
+		.max_fifo_lines	= 2,
+	}, {
+		.ipu_channel	= 29,
+		.channel_reg	= DMFC_DP_CHAN,
+		.shift		= DMFC_DP_CHAN_6F_29,
+		.eot_shift	= 23,
+		.max_fifo_lines	= 1,
+	},
+};
+
+#define DMFC_NUM_CHANNELS	ARRAY_SIZE(dmfcdata)
+
+struct ipu_dmfc_priv;
+
+struct dmfc_channel {
+	unsigned			slots;
+	struct ipu_soc			*ipu;
+	struct ipu_dmfc_priv		*priv;
+	const struct dmfc_channel_data	*data;
+};
+
+struct ipu_dmfc_priv {
+	struct ipu_soc *ipu;
+	struct device *dev;
+	struct dmfc_channel channels[DMFC_NUM_CHANNELS];
+	struct mutex mutex;
+	void __iomem *base;
+	int use_count;
+};
+
+int ipu_dmfc_enable_channel(struct dmfc_channel *dmfc)
+{
+	struct ipu_dmfc_priv *priv = dmfc->priv;
+	mutex_lock(&priv->mutex);
+
+	if (!priv->use_count)
+		ipu_module_enable(priv->ipu, IPU_CONF_DMFC_EN);
+
+	priv->use_count++;
+
+	mutex_unlock(&priv->mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ipu_dmfc_enable_channel);
+
+void ipu_dmfc_disable_channel(struct dmfc_channel *dmfc)
+{
+	struct ipu_dmfc_priv *priv = dmfc->priv;
+
+	mutex_lock(&priv->mutex);
+
+	priv->use_count--;
+
+	if (!priv->use_count)
+		ipu_module_disable(priv->ipu, IPU_CONF_DMFC_EN);
+
+	if (priv->use_count < 0)
+		priv->use_count = 0;
+
+	mutex_unlock(&priv->mutex);
+}
+EXPORT_SYMBOL_GPL(ipu_dmfc_disable_channel);
+
+void ipu_dmfc_config_wait4eot(struct dmfc_channel *dmfc, int width)
+{
+	struct ipu_dmfc_priv *priv = dmfc->priv;
+	u32 dmfc_gen1;
+
+	mutex_lock(&priv->mutex);
+
+	dmfc_gen1 = readl(priv->base + DMFC_GENERAL1);
+
+	if ((dmfc->slots * 64 * 4) / width > dmfc->data->max_fifo_lines)
+		dmfc_gen1 |= 1 << dmfc->data->eot_shift;
+	else
+		dmfc_gen1 &= ~(1 << dmfc->data->eot_shift);
+
+	writel(dmfc_gen1, priv->base + DMFC_GENERAL1);
+
+	mutex_unlock(&priv->mutex);
+}
+EXPORT_SYMBOL_GPL(ipu_dmfc_config_wait4eot);
+
+struct dmfc_channel *ipu_dmfc_get(struct ipu_soc *ipu, int ipu_channel)
+{
+	struct ipu_dmfc_priv *priv = ipu->dmfc_priv;
+	int i;
+
+	for (i = 0; i < DMFC_NUM_CHANNELS; i++)
+		if (dmfcdata[i].ipu_channel == ipu_channel)
+			return &priv->channels[i];
+	return ERR_PTR(-ENODEV);
+}
+EXPORT_SYMBOL_GPL(ipu_dmfc_get);
+
+void ipu_dmfc_put(struct dmfc_channel *dmfc)
+{
+}
+EXPORT_SYMBOL_GPL(ipu_dmfc_put);
+
+int ipu_dmfc_init(struct ipu_soc *ipu, struct device *dev, unsigned long base,
+		struct clk *ipu_clk)
+{
+	struct ipu_dmfc_priv *priv;
+	int i;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_ioremap(dev, base, PAGE_SIZE);
+	if (!priv->base)
+		return -ENOMEM;
+
+	priv->dev = dev;
+	priv->ipu = ipu;
+	mutex_init(&priv->mutex);
+
+	ipu->dmfc_priv = priv;
+
+	for (i = 0; i < DMFC_NUM_CHANNELS; i++) {
+		priv->channels[i].priv = priv;
+		priv->channels[i].ipu = ipu;
+		priv->channels[i].data = &dmfcdata[i];
+
+		if (dmfcdata[i].ipu_channel == IPUV3_CHANNEL_MEM_BG_SYNC ||
+		    dmfcdata[i].ipu_channel == IPUV3_CHANNEL_MEM_FG_SYNC ||
+		    dmfcdata[i].ipu_channel == IPUV3_CHANNEL_MEM_DC_SYNC)
+			priv->channels[i].slots = 2;
+	}
+
+	writel(0x00000050, priv->base + DMFC_WR_CHAN);
+	writel(0x00005654, priv->base + DMFC_DP_CHAN);
+	writel(0x202020f6, priv->base + DMFC_WR_CHAN_DEF);
+	writel(0x2020f6f6, priv->base + DMFC_DP_CHAN_DEF);
+	writel(0x00000003, priv->base + DMFC_GENERAL1);
+
+	return 0;
+}
+
+void ipu_dmfc_exit(struct ipu_soc *ipu)
+{
+}