From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda 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 Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- Documentation/input/devices/rotary-encoder.rst | 135 +++++++++++++++++++++++++ 1 file changed, 135 insertions(+) create mode 100644 Documentation/input/devices/rotary-encoder.rst (limited to 'Documentation/input/devices/rotary-encoder.rst') diff --git a/Documentation/input/devices/rotary-encoder.rst b/Documentation/input/devices/rotary-encoder.rst new file mode 100644 index 000000000..5865748c1 --- /dev/null +++ b/Documentation/input/devices/rotary-encoder.rst @@ -0,0 +1,135 @@ +============================================================ +rotary-encoder - a generic driver for GPIO connected devices +============================================================ + +:Author: Daniel Mack , Feb 2009 + +Function +-------- + +Rotary encoders are devices which are connected to the CPU or other +peripherals with two wires. The outputs are phase-shifted by 90 degrees +and by triggering on falling and rising edges, the turn direction can +be determined. + +Some encoders have both outputs low in stable states, others also have +a stable state with both outputs high (half-period mode) and some have +a stable state in all steps (quarter-period mode). + +The phase diagram of these two outputs look like this:: + + _____ _____ _____ + | | | | | | + Channel A ____| |_____| |_____| |____ + + : : : : : : : : : : : : + __ _____ _____ _____ + | | | | | | | + Channel B |_____| |_____| |_____| |__ + + : : : : : : : : : : : : + Event a b c d a b c d a b c d + + |<-------->| + one step + + |<-->| + one step (half-period mode) + + |<>| + one step (quarter-period mode) + +For more information, please see + https://en.wikipedia.org/wiki/Rotary_encoder + + +Events / state machine +---------------------- + +In half-period mode, state a) and c) above are used to determine the +rotational direction based on the last stable state. Events are reported in +states b) and d) given that the new stable state is different from the last +(i.e. the rotation was not reversed half-way). + +Otherwise, the following apply: + +a) Rising edge on channel A, channel B in low state + This state is used to recognize a clockwise turn + +b) Rising edge on channel B, channel A in high state + When entering this state, the encoder is put into 'armed' state, + meaning that there it has seen half the way of a one-step transition. + +c) Falling edge on channel A, channel B in high state + This state is used to recognize a counter-clockwise turn + +d) Falling edge on channel B, channel A in low state + Parking position. If the encoder enters this state, a full transition + should have happened, unless it flipped back on half the way. The + 'armed' state tells us about that. + +Platform requirements +--------------------- + +As there is no hardware dependent call in this driver, the platform it is +used with must support gpiolib. Another requirement is that IRQs must be +able to fire on both edges. + + +Board integration +----------------- + +To use this driver in your system, register a platform_device with the +name 'rotary-encoder' and associate the IRQs and some specific platform +data with it. Because the driver uses generic device properties, this can +be done either via device tree, ACPI, or using static board files, like in +example below: + +:: + + /* board support file example */ + + #include + #include + #include + + #define GPIO_ROTARY_A 1 + #define GPIO_ROTARY_B 2 + + static struct gpiod_lookup_table rotary_encoder_gpios = { + .dev_id = "rotary-encoder.0", + .table = { + GPIO_LOOKUP_IDX("gpio-0", + GPIO_ROTARY_A, NULL, 0, GPIO_ACTIVE_LOW), + GPIO_LOOKUP_IDX("gpio-0", + GPIO_ROTARY_B, NULL, 1, GPIO_ACTIVE_HIGH), + { }, + }, + }; + + static const struct property_entry rotary_encoder_properties[] = { + PROPERTY_ENTRY_U32("rotary-encoder,steps-per-period", 24), + PROPERTY_ENTRY_U32("linux,axis", ABS_X), + PROPERTY_ENTRY_U32("rotary-encoder,relative_axis", 0), + { }, + }; + + static const struct software_node rotary_encoder_node = { + .properties = rotary_encoder_properties, + }; + + static struct platform_device rotary_encoder_device = { + .name = "rotary-encoder", + .id = 0, + }; + + ... + + gpiod_add_lookup_table(&rotary_encoder_gpios); + device_add_software_node(&rotary_encoder_device.dev, &rotary_encoder_node); + platform_device_register(&rotary_encoder_device); + + ... + +Please consult device tree binding documentation to see all properties +supported by the driver. -- cgit v1.3.1