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, 376 insertions, 0 deletions

diff --git a/drivers/gpu/ipu-v3/ipu-dp.c b/drivers/gpu/ipu-v3/ipu-dp.c
new file mode 100644
index 000000000..6a558205d
--- /dev/null
+++ b/drivers/gpu/ipu-v3/ipu-dp.c
@@ -0,0 +1,376 @@
+// 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/kernel.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+#include <linux/err.h>
+
+#include <drm/drm_color_mgmt.h>
+#include <video/imx-ipu-v3.h>
+#include "ipu-prv.h"
+
+#define DP_SYNC 0
+#define DP_ASYNC0 0x60
+#define DP_ASYNC1 0xBC
+
+#define DP_COM_CONF		0x0
+#define DP_GRAPH_WIND_CTRL	0x0004
+#define DP_FG_POS		0x0008
+#define DP_CSC_A_0		0x0044
+#define DP_CSC_A_1		0x0048
+#define DP_CSC_A_2		0x004C
+#define DP_CSC_A_3		0x0050
+#define DP_CSC_0		0x0054
+#define DP_CSC_1		0x0058
+
+#define DP_COM_CONF_FG_EN		(1 << 0)
+#define DP_COM_CONF_GWSEL		(1 << 1)
+#define DP_COM_CONF_GWAM		(1 << 2)
+#define DP_COM_CONF_GWCKE		(1 << 3)
+#define DP_COM_CONF_CSC_DEF_MASK	(3 << 8)
+#define DP_COM_CONF_CSC_DEF_OFFSET	8
+#define DP_COM_CONF_CSC_DEF_FG		(3 << 8)
+#define DP_COM_CONF_CSC_DEF_BG		(2 << 8)
+#define DP_COM_CONF_CSC_DEF_BOTH	(1 << 8)
+
+#define IPUV3_NUM_FLOWS		3
+
+struct ipu_dp_priv;
+
+struct ipu_dp {
+	u32 flow;
+	bool in_use;
+	bool foreground;
+	enum ipu_color_space in_cs;
+};
+
+struct ipu_flow {
+	struct ipu_dp foreground;
+	struct ipu_dp background;
+	enum ipu_color_space out_cs;
+	void __iomem *base;
+	struct ipu_dp_priv *priv;
+};
+
+struct ipu_dp_priv {
+	struct ipu_soc *ipu;
+	struct device *dev;
+	void __iomem *base;
+	struct ipu_flow flow[IPUV3_NUM_FLOWS];
+	struct mutex mutex;
+	int use_count;
+};
+
+static u32 ipu_dp_flow_base[] = {DP_SYNC, DP_ASYNC0, DP_ASYNC1};
+
+static inline struct ipu_flow *to_flow(struct ipu_dp *dp)
+{
+	if (dp->foreground)
+		return container_of(dp, struct ipu_flow, foreground);
+	else
+		return container_of(dp, struct ipu_flow, background);
+}
+
+int ipu_dp_set_global_alpha(struct ipu_dp *dp, bool enable,
+		u8 alpha, bool bg_chan)
+{
+	struct ipu_flow *flow = to_flow(dp);
+	struct ipu_dp_priv *priv = flow->priv;
+	u32 reg;
+
+	mutex_lock(&priv->mutex);
+
+	reg = readl(flow->base + DP_COM_CONF);
+	if (bg_chan)
+		reg &= ~DP_COM_CONF_GWSEL;
+	else
+		reg |= DP_COM_CONF_GWSEL;
+	writel(reg, flow->base + DP_COM_CONF);
+
+	if (enable) {
+		reg = readl(flow->base + DP_GRAPH_WIND_CTRL) & 0x00FFFFFFL;
+		writel(reg | ((u32) alpha << 24),
+			     flow->base + DP_GRAPH_WIND_CTRL);
+
+		reg = readl(flow->base + DP_COM_CONF);
+		writel(reg | DP_COM_CONF_GWAM, flow->base + DP_COM_CONF);
+	} else {
+		reg = readl(flow->base + DP_COM_CONF);
+		writel(reg & ~DP_COM_CONF_GWAM, flow->base + DP_COM_CONF);
+	}
+
+	ipu_srm_dp_update(priv->ipu, true);
+
+	mutex_unlock(&priv->mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ipu_dp_set_global_alpha);
+
+int ipu_dp_set_window_pos(struct ipu_dp *dp, u16 x_pos, u16 y_pos)
+{
+	struct ipu_flow *flow = to_flow(dp);
+	struct ipu_dp_priv *priv = flow->priv;
+
+	writel((x_pos << 16) | y_pos, flow->base + DP_FG_POS);
+
+	ipu_srm_dp_update(priv->ipu, true);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ipu_dp_set_window_pos);
+
+static void ipu_dp_csc_init(struct ipu_flow *flow,
+		enum drm_color_encoding ycbcr_enc,
+		enum drm_color_range range,
+		enum ipu_color_space in,
+		enum ipu_color_space out,
+		u32 place)
+{
+	u32 reg;
+
+	reg = readl(flow->base + DP_COM_CONF);
+	reg &= ~DP_COM_CONF_CSC_DEF_MASK;
+
+	if (in == out) {
+		writel(reg, flow->base + DP_COM_CONF);
+		return;
+	}
+
+	if (in == IPUV3_COLORSPACE_RGB && out == IPUV3_COLORSPACE_YUV) {
+		writel(0x099 | (0x12d << 16), flow->base + DP_CSC_A_0);
+		writel(0x03a | (0x3a9 << 16), flow->base + DP_CSC_A_1);
+		writel(0x356 | (0x100 << 16), flow->base + DP_CSC_A_2);
+		writel(0x100 | (0x329 << 16), flow->base + DP_CSC_A_3);
+		writel(0x3d6 | (0x0000 << 16) | (2 << 30),
+				flow->base + DP_CSC_0);
+		writel(0x200 | (2 << 14) | (0x200 << 16) | (2 << 30),
+				flow->base + DP_CSC_1);
+	} else if (ycbcr_enc == DRM_COLOR_YCBCR_BT709) {
+		/* Rec.709 limited range */
+		writel(0x095 | (0x000 << 16), flow->base + DP_CSC_A_0);
+		writel(0x0e5 | (0x095 << 16), flow->base + DP_CSC_A_1);
+		writel(0x3e5 | (0x3bc << 16), flow->base + DP_CSC_A_2);
+		writel(0x095 | (0x10e << 16), flow->base + DP_CSC_A_3);
+		writel(0x000 | (0x3e10 << 16) | (1 << 30),
+				flow->base + DP_CSC_0);
+		writel(0x09a | (1 << 14) | (0x3dbe << 16) | (1 << 30),
+				flow->base + DP_CSC_1);
+	} else {
+		/* BT.601 limited range */
+		writel(0x095 | (0x000 << 16), flow->base + DP_CSC_A_0);
+		writel(0x0cc | (0x095 << 16), flow->base + DP_CSC_A_1);
+		writel(0x3ce | (0x398 << 16), flow->base + DP_CSC_A_2);
+		writel(0x095 | (0x0ff << 16), flow->base + DP_CSC_A_3);
+		writel(0x000 | (0x3e42 << 16) | (1 << 30),
+				flow->base + DP_CSC_0);
+		writel(0x10a | (1 << 14) | (0x3dd6 << 16) | (1 << 30),
+				flow->base + DP_CSC_1);
+	}
+
+	reg |= place;
+
+	writel(reg, flow->base + DP_COM_CONF);
+}
+
+int ipu_dp_setup_channel(struct ipu_dp *dp,
+		enum drm_color_encoding ycbcr_enc,
+		enum drm_color_range range,
+		enum ipu_color_space in,
+		enum ipu_color_space out)
+{
+	struct ipu_flow *flow = to_flow(dp);
+	struct ipu_dp_priv *priv = flow->priv;
+
+	mutex_lock(&priv->mutex);
+
+	dp->in_cs = in;
+
+	if (!dp->foreground)
+		flow->out_cs = out;
+
+	if (flow->foreground.in_cs == flow->background.in_cs) {
+		/*
+		 * foreground and background are of same colorspace, put
+		 * colorspace converter after combining unit.
+		 */
+		ipu_dp_csc_init(flow, ycbcr_enc, range,
+				flow->foreground.in_cs, flow->out_cs,
+				DP_COM_CONF_CSC_DEF_BOTH);
+	} else {
+		if (flow->foreground.in_cs == IPUV3_COLORSPACE_UNKNOWN ||
+		    flow->foreground.in_cs == flow->out_cs)
+			/*
+			 * foreground identical to output, apply color
+			 * conversion on background
+			 */
+			ipu_dp_csc_init(flow, ycbcr_enc, range,
+					flow->background.in_cs,
+					flow->out_cs, DP_COM_CONF_CSC_DEF_BG);
+		else
+			ipu_dp_csc_init(flow, ycbcr_enc, range,
+					flow->foreground.in_cs,
+					flow->out_cs, DP_COM_CONF_CSC_DEF_FG);
+	}
+
+	ipu_srm_dp_update(priv->ipu, true);
+
+	mutex_unlock(&priv->mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ipu_dp_setup_channel);
+
+int ipu_dp_enable(struct ipu_soc *ipu)
+{
+	struct ipu_dp_priv *priv = ipu->dp_priv;
+
+	mutex_lock(&priv->mutex);
+
+	if (!priv->use_count)
+		ipu_module_enable(priv->ipu, IPU_CONF_DP_EN);
+
+	priv->use_count++;
+
+	mutex_unlock(&priv->mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ipu_dp_enable);
+
+int ipu_dp_enable_channel(struct ipu_dp *dp)
+{
+	struct ipu_flow *flow = to_flow(dp);
+	struct ipu_dp_priv *priv = flow->priv;
+	u32 reg;
+
+	if (!dp->foreground)
+		return 0;
+
+	mutex_lock(&priv->mutex);
+
+	reg = readl(flow->base + DP_COM_CONF);
+	reg |= DP_COM_CONF_FG_EN;
+	writel(reg, flow->base + DP_COM_CONF);
+
+	ipu_srm_dp_update(priv->ipu, true);
+
+	mutex_unlock(&priv->mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(ipu_dp_enable_channel);
+
+void ipu_dp_disable_channel(struct ipu_dp *dp, bool sync)
+{
+	struct ipu_flow *flow = to_flow(dp);
+	struct ipu_dp_priv *priv = flow->priv;
+	u32 reg, csc;
+
+	dp->in_cs = IPUV3_COLORSPACE_UNKNOWN;
+
+	if (!dp->foreground)
+		return;
+
+	mutex_lock(&priv->mutex);
+
+	reg = readl(flow->base + DP_COM_CONF);
+	csc = reg & DP_COM_CONF_CSC_DEF_MASK;
+	reg &= ~DP_COM_CONF_CSC_DEF_MASK;
+	if (csc == DP_COM_CONF_CSC_DEF_BOTH || csc == DP_COM_CONF_CSC_DEF_BG)
+		reg |= DP_COM_CONF_CSC_DEF_BG;
+
+	reg &= ~DP_COM_CONF_FG_EN;
+	writel(reg, flow->base + DP_COM_CONF);
+
+	writel(0, flow->base + DP_FG_POS);
+	ipu_srm_dp_update(priv->ipu, sync);
+
+	mutex_unlock(&priv->mutex);
+}
+EXPORT_SYMBOL_GPL(ipu_dp_disable_channel);
+
+void ipu_dp_disable(struct ipu_soc *ipu)
+{
+	struct ipu_dp_priv *priv = ipu->dp_priv;
+
+	mutex_lock(&priv->mutex);
+
+	priv->use_count--;
+
+	if (!priv->use_count)
+		ipu_module_disable(priv->ipu, IPU_CONF_DP_EN);
+
+	if (priv->use_count < 0)
+		priv->use_count = 0;
+
+	mutex_unlock(&priv->mutex);
+}
+EXPORT_SYMBOL_GPL(ipu_dp_disable);
+
+struct ipu_dp *ipu_dp_get(struct ipu_soc *ipu, unsigned int flow)
+{
+	struct ipu_dp_priv *priv = ipu->dp_priv;
+	struct ipu_dp *dp;
+
+	if ((flow >> 1) >= IPUV3_NUM_FLOWS)
+		return ERR_PTR(-EINVAL);
+
+	if (flow & 1)
+		dp = &priv->flow[flow >> 1].foreground;
+	else
+		dp = &priv->flow[flow >> 1].background;
+
+	if (dp->in_use)
+		return ERR_PTR(-EBUSY);
+
+	dp->in_use = true;
+
+	return dp;
+}
+EXPORT_SYMBOL_GPL(ipu_dp_get);
+
+void ipu_dp_put(struct ipu_dp *dp)
+{
+	dp->in_use = false;
+}
+EXPORT_SYMBOL_GPL(ipu_dp_put);
+
+int ipu_dp_init(struct ipu_soc *ipu, struct device *dev, unsigned long base)
+{
+	struct ipu_dp_priv *priv;
+	int i;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	priv->dev = dev;
+	priv->ipu = ipu;
+
+	ipu->dp_priv = priv;
+
+	priv->base = devm_ioremap(dev, base, PAGE_SIZE);
+	if (!priv->base)
+		return -ENOMEM;
+
+	mutex_init(&priv->mutex);
+
+	for (i = 0; i < IPUV3_NUM_FLOWS; i++) {
+		priv->flow[i].background.in_cs = IPUV3_COLORSPACE_UNKNOWN;
+		priv->flow[i].foreground.in_cs = IPUV3_COLORSPACE_UNKNOWN;
+		priv->flow[i].foreground.foreground = true;
+		priv->flow[i].base = priv->base + ipu_dp_flow_base[i];
+		priv->flow[i].priv = priv;
+	}
+
+	return 0;
+}
+
+void ipu_dp_exit(struct ipu_soc *ipu)
+{
+}