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, 134 insertions, 0 deletions

diff --git a/Documentation/usb/chipidea.rst b/Documentation/usb/chipidea.rst
new file mode 100644
index 000000000..d9920c24e
--- /dev/null
+++ b/Documentation/usb/chipidea.rst
@@ -0,0 +1,134 @@
+==============================================
+ChipIdea Highspeed Dual Role Controller Driver
+==============================================
+
+1. How to test OTG FSM(HNP and SRP)
+-----------------------------------
+
+To show how to demo OTG HNP and SRP functions via sys input files
+with 2 Freescale i.MX6Q sabre SD boards.
+
+1.1 How to enable OTG FSM
+-------------------------
+
+1.1.1 Select CONFIG_USB_OTG_FSM in menuconfig, rebuild kernel
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Image and modules. If you want to check some internal
+variables for otg fsm, mount debugfs, there are 2 files
+which can show otg fsm variables and some controller registers value::
+
+	cat /sys/kernel/debug/ci_hdrc.0/otg
+	cat /sys/kernel/debug/ci_hdrc.0/registers
+
+1.1.2 Add below entries in your dts file for your controller node
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+::
+
+	otg-rev = <0x0200>;
+	adp-disable;
+
+1.2 Test operations
+-------------------
+
+1) Power up 2 Freescale i.MX6Q sabre SD boards with gadget class driver loaded
+   (e.g. g_mass_storage).
+
+2) Connect 2 boards with usb cable: one end is micro A plug, the other end
+   is micro B plug.
+
+   The A-device (with micro A plug inserted) should enumerate B-device.
+
+3) Role switch
+
+   On B-device::
+
+	echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req
+
+   B-device should take host role and enumerate A-device.
+
+4) A-device switch back to host.
+
+   On B-device::
+
+	echo 0 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req
+
+   or, by introducing HNP polling, B-Host can know when A-peripheral wishes to
+   be in the host role, so this role switch also can be triggered in
+   A-peripheral side by answering the polling from B-Host. This can be done on
+   A-device::
+
+	echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_req
+
+   A-device should switch back to host and enumerate B-device.
+
+5) Remove B-device (unplug micro B plug) and insert again in 10 seconds;
+   A-device should enumerate B-device again.
+
+6) Remove B-device (unplug micro B plug) and insert again after 10 seconds;
+   A-device should NOT enumerate B-device.
+
+   if A-device wants to use bus:
+
+   On A-device::
+
+	echo 0 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_drop
+	echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_req
+
+   if B-device wants to use bus:
+
+   On B-device::
+
+	echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req
+
+7) A-device power down the bus.
+
+   On A-device::
+
+	echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_drop
+
+   A-device should disconnect with B-device and power down the bus.
+
+8) B-device does data pulse for SRP.
+
+   On B-device::
+
+	echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req
+
+   A-device should resume usb bus and enumerate B-device.
+
+1.3 Reference document
+----------------------
+"On-The-Go and Embedded Host Supplement to the USB Revision 2.0 Specification
+July 27, 2012 Revision 2.0 version 1.1a"
+
+2. How to enable USB as system wakeup source
+--------------------------------------------
+Below is the example for how to enable USB as system wakeup source
+on an imx6 platform.
+
+2.1 Enable core's wakeup::
+
+	echo enabled > /sys/bus/platform/devices/ci_hdrc.0/power/wakeup
+
+2.2 Enable glue layer's wakeup::
+
+	echo enabled > /sys/bus/platform/devices/2184000.usb/power/wakeup
+
+2.3 Enable PHY's wakeup (optional)::
+
+	echo enabled > /sys/bus/platform/devices/20c9000.usbphy/power/wakeup
+
+2.4 Enable roothub's wakeup::
+
+	echo enabled > /sys/bus/usb/devices/usb1/power/wakeup
+
+2.5 Enable related device's wakeup::
+
+	echo enabled > /sys/bus/usb/devices/1-1/power/wakeup
+
+If the system has only one usb port, and you want usb wakeup at this port, you
+can use the below script to enable usb wakeup::
+
+	for i in $(find /sys -name wakeup | grep usb);do echo enabled > $i;done;