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, 81 insertions, 0 deletions

diff --git a/Documentation/driver-api/backlight/lp855x-driver.rst b/Documentation/driver-api/backlight/lp855x-driver.rst
new file mode 100644
index 000000000..1e0b224fc
--- /dev/null
+++ b/Documentation/driver-api/backlight/lp855x-driver.rst
@@ -0,0 +1,81 @@
+====================
+Kernel driver lp855x
+====================
+
+Backlight driver for LP855x ICs
+
+Supported chips:
+
+	Texas Instruments LP8550, LP8551, LP8552, LP8553, LP8555, LP8556 and
+	LP8557
+
+Author: Milo(Woogyom) Kim <milo.kim@ti.com>
+
+Description
+-----------
+
+* Brightness control
+
+  Brightness can be controlled by the pwm input or the i2c command.
+  The lp855x driver supports both cases.
+
+* Device attributes
+
+  1) bl_ctl_mode
+
+  Backlight control mode.
+
+  Value: pwm based or register based
+
+  2) chip_id
+
+  The lp855x chip id.
+
+  Value: lp8550/lp8551/lp8552/lp8553/lp8555/lp8556/lp8557
+
+Platform data for lp855x
+------------------------
+
+For supporting platform specific data, the lp855x platform data can be used.
+
+* name:
+	Backlight driver name. If it is not defined, default name is set.
+* device_control:
+	Value of DEVICE CONTROL register.
+* initial_brightness:
+	Initial value of backlight brightness.
+* period_ns:
+	Platform specific PWM period value. unit is nano.
+	Only valid when brightness is pwm input mode.
+* size_program:
+	Total size of lp855x_rom_data.
+* rom_data:
+	List of new eeprom/eprom registers.
+
+Examples
+========
+
+1) lp8552 platform data: i2c register mode with new eeprom data::
+
+    #define EEPROM_A5_ADDR	0xA5
+    #define EEPROM_A5_VAL	0x4f	/* EN_VSYNC=0 */
+
+    static struct lp855x_rom_data lp8552_eeprom_arr[] = {
+	{EEPROM_A5_ADDR, EEPROM_A5_VAL},
+    };
+
+    static struct lp855x_platform_data lp8552_pdata = {
+	.name = "lcd-bl",
+	.device_control = I2C_CONFIG(LP8552),
+	.initial_brightness = INITIAL_BRT,
+	.size_program = ARRAY_SIZE(lp8552_eeprom_arr),
+	.rom_data = lp8552_eeprom_arr,
+    };
+
+2) lp8556 platform data: pwm input mode with default rom data::
+
+    static struct lp855x_platform_data lp8556_pdata = {
+	.device_control = PWM_CONFIG(LP8556),
+	.initial_brightness = INITIAL_BRT,
+	.period_ns = 1000000,
+    };