From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001
From: Miguel Ojeda <ojeda@kernel.org>
Date: Sun, 16 Aug 2026 15:32:33 +0200
Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers

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>
---
 drivers/video/fbdev/n411.c | 208 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 208 insertions(+)
 create mode 100644 drivers/video/fbdev/n411.c

(limited to 'drivers/video/fbdev/n411.c')

diff --git a/drivers/video/fbdev/n411.c b/drivers/video/fbdev/n411.c
new file mode 100644
index 000000000..a36773133
--- /dev/null
+++ b/drivers/video/fbdev/n411.c
@@ -0,0 +1,208 @@
+/*
+ * linux/drivers/video/n411.c -- Platform device for N411 EPD kit
+ *
+ * Copyright (C) 2008, Jaya Kumar
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file COPYING in the main directory of this archive for
+ * more details.
+ *
+ * Layout is based on skeletonfb.c by James Simmons and Geert Uytterhoeven.
+ *
+ * This driver is written to be used with the Hecuba display controller
+ * board, and tested with the EInk 800x600 display in 1 bit mode.
+ * The interface between Hecuba and the host is TTL based GPIO. The
+ * GPIO requirements are 8 writable data lines and 6 lines for control.
+ * Only 4 of the controls are actually used here but 6 for future use.
+ * The driver requires the IO addresses for data and control GPIO at
+ * load time. It is also possible to use this display with a standard
+ * PC parallel port.
+ *
+ * General notes:
+ * - User must set dio_addr=0xIOADDR cio_addr=0xIOADDR c2io_addr=0xIOADDR
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/fb.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/uaccess.h>
+#include <linux/irq.h>
+
+#include <video/hecubafb.h>
+
+static unsigned long dio_addr;
+static unsigned long cio_addr;
+static unsigned long c2io_addr;
+static unsigned long splashval;
+static unsigned int nosplash;
+static unsigned char ctl;
+
+static void n411_set_ctl(struct hecubafb_par *par, unsigned char bit, unsigned
+							char state)
+{
+	switch (bit) {
+	case HCB_CD_BIT:
+		if (state)
+			ctl &= ~(HCB_CD_BIT);
+		else
+			ctl |= HCB_CD_BIT;
+		break;
+	case HCB_DS_BIT:
+		if (state)
+			ctl &= ~(HCB_DS_BIT);
+		else
+			ctl |= HCB_DS_BIT;
+		break;
+	}
+	outb(ctl, cio_addr);
+}
+
+static unsigned char n411_get_ctl(struct hecubafb_par *par)
+{
+	return inb(c2io_addr);
+}
+
+static void n411_set_data(struct hecubafb_par *par, unsigned char value)
+{
+	outb(value, dio_addr);
+}
+
+static void n411_wait_for_ack(struct hecubafb_par *par, int clear)
+{
+	int timeout;
+	unsigned char tmp;
+
+	timeout = 500;
+	do {
+		tmp = n411_get_ctl(par);
+		if ((tmp & HCB_ACK_BIT) && (!clear))
+			return;
+		else if (!(tmp & HCB_ACK_BIT) && (clear))
+			return;
+		udelay(1);
+	} while (timeout--);
+	printk(KERN_ERR "timed out waiting for ack\n");
+}
+
+static int n411_init_control(struct hecubafb_par *par)
+{
+	unsigned char tmp;
+	/* for init, we want the following setup to be set:
+	WUP = lo
+	ACK = hi
+	DS = hi
+	RW = hi
+	CD = lo
+	*/
+
+	/* write WUP to lo, DS to hi, RW to hi, CD to lo */
+	ctl = HCB_WUP_BIT | HCB_RW_BIT | HCB_CD_BIT ;
+	n411_set_ctl(par, HCB_DS_BIT, 1);
+
+	/* check ACK is not lo */
+	tmp = n411_get_ctl(par);
+	if (tmp & HCB_ACK_BIT) {
+		printk(KERN_ERR "Fail because ACK is already low\n");
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+
+static int n411_init_board(struct hecubafb_par *par)
+{
+	int retval;
+
+	retval = n411_init_control(par);
+	if (retval)
+		return retval;
+
+	par->send_command(par, APOLLO_INIT_DISPLAY);
+	par->send_data(par, 0x81);
+
+	/* have to wait while display resets */
+	udelay(1000);
+
+	/* if we were told to splash the screen, we just clear it */
+	if (!nosplash) {
+		par->send_command(par, APOLLO_ERASE_DISPLAY);
+		par->send_data(par, splashval);
+	}
+
+	return 0;
+}
+
+static struct hecuba_board n411_board = {
+	.owner			= THIS_MODULE,
+	.init			= n411_init_board,
+	.set_ctl		= n411_set_ctl,
+	.set_data		= n411_set_data,
+	.wait_for_ack		= n411_wait_for_ack,
+};
+
+static struct platform_device *n411_device;
+static int __init n411_init(void)
+{
+	int ret;
+	if (!dio_addr || !cio_addr || !c2io_addr) {
+		printk(KERN_WARNING "no IO addresses supplied\n");
+		return -EINVAL;
+	}
+
+	/* request our platform independent driver */
+	request_module("hecubafb");
+
+	n411_device = platform_device_alloc("hecubafb", -1);
+	if (!n411_device)
+		return -ENOMEM;
+
+	ret = platform_device_add_data(n411_device, &n411_board,
+				       sizeof(n411_board));
+	if (ret)
+		goto put_plat_device;
+
+	/* this _add binds hecubafb to n411. hecubafb refcounts n411 */
+	ret = platform_device_add(n411_device);
+
+	if (ret)
+		goto put_plat_device;
+
+	return 0;
+
+put_plat_device:
+	platform_device_put(n411_device);
+	return ret;
+}
+
+static void __exit n411_exit(void)
+{
+	platform_device_unregister(n411_device);
+}
+
+module_init(n411_init);
+module_exit(n411_exit);
+
+module_param(nosplash, uint, 0);
+MODULE_PARM_DESC(nosplash, "Disable doing the splash screen");
+module_param_hw(dio_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(dio_addr, "IO address for data, eg: 0x480");
+module_param_hw(cio_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(cio_addr, "IO address for control, eg: 0x400");
+module_param_hw(c2io_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(c2io_addr, "IO address for secondary control, eg: 0x408");
+module_param(splashval, ulong, 0);
+MODULE_PARM_DESC(splashval, "Splash pattern: 0x00 is black, 0x01 is white");
+
+MODULE_DESCRIPTION("board driver for n411 hecuba/apollo epd kit");
+MODULE_AUTHOR("Jaya Kumar");
+MODULE_LICENSE("GPL");
+
-- 
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