examples: linux: add rpmsg udev rules and scripts

examples/linux/rpmsg_udev_scripts/99-rpmsg.rules

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+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (C) 2026, Advanced Micro Devices, Inc.
+
+# Skip rpmsg_ctrl and rpmsg_ns devices by name using GOTO
+SUBSYSTEM=="rpmsg", ACTION=="add", \
+    KERNEL=="virtio*.rpmsg_ctrl.0.0", GOTO="rpmsg_end"
+
+SUBSYSTEM=="rpmsg", ACTION=="add", \
+    KERNEL=="virtio*.rpmsg_ns.53.53", GOTO="rpmsg_end"
+
+SUBSYSTEM=="rpmsg", ACTION=="add", \
+    KERNEL=="rpmsg_ctrl[0-9]*", GOTO="rpmsg_end"
+
+SUBSYSTEM=="rpmsg", ACTION=="remove", \
+    KERNEL=="rpmsg_ctrl[0-9]*", GOTO="rpmsg_end"
+
+# rpmsg endpoint creation rule
+SUBSYSTEM=="rpmsg", KERNEL=="rpmsg[0-9]*", ACTION=="add", \
+        GROUP="rpmsg", MODE="0660", \
+        RUN+="/usr/bin/rpmsg_add_ept_symlink.sh %k", GOTO="rpmsg_end"
+
+# rpmsg endpoint creation rule
+SUBSYSTEM=="rpmsg", KERNEL=="rpmsg[0-9]*", ACTION=="remove", \
+        RUN+="/usr/bin/rpmsg_remove_ept_symlink.sh %k", GOTO="rpmsg_end"
+
+# rpmsg channel creation rule
+SUBSYSTEM=="rpmsg", ACTION=="add", RUN+="/usr/bin/rpmsg_create_channel.sh %k"
+
+# ttyRPMSG device permission rule
+SUBSYSTEM=="tty", KERNEL=="ttyRPMSG[0-9]*", ACTION=="add", \
+    GROUP="rpmsg", MODE="0660"
+
+LABEL="rpmsg_end"

examples/linux/rpmsg_udev_scripts/Makefile

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+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (C) 2026, Advanced Micro Devices, Inc.
+
+prefix ?= /usr
+bindir ?= $(prefix)/bin
+udevdir ?= /etc/udev/rules.d
+
+INSTALL ?= install
+INSTALL_PROGRAM ?= $(INSTALL) -m 0755
+INSTALL_DATA ?= $(INSTALL) -m 0644
+
+SCRIPTS := \
+	rpmsg_add_ept_symlink.sh \
+	rpmsg_create_channel.sh \
+	rpmsg_remove_ept_symlink.sh
+
+UDEV_RULES := 99-rpmsg.rules
+
+.PHONY: all install uninstall clean
+
+all:
+
+install:
+	$(INSTALL) -d "$(DESTDIR)$(bindir)"
+	$(INSTALL) -d "$(DESTDIR)$(udevdir)"
+	$(INSTALL_PROGRAM) $(SCRIPTS) "$(DESTDIR)$(bindir)"
+	$(INSTALL_DATA) $(UDEV_RULES) "$(DESTDIR)$(udevdir)"
+
+uninstall:
+	$(RM) $(addprefix "$(DESTDIR)$(bindir)"/,$(SCRIPTS))
+	$(RM) $(addprefix "$(DESTDIR)$(udevdir)"/,$(UDEV_RULES))
+
+clean:

examples/linux/rpmsg_udev_scripts/README.md

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+# RPMsg udev Scripts
+
+Udev rules and helper scripts to automatically manage RPMsg endpoint devices.
+When an RPMsg channel is created by the remote processor, these scripts handle
+device permissions, symlink creation, and endpoint export automatically.
+
+## Files
+
+| File | Description |
+|------|-------------|
+| `99-rpmsg.rules` | udev rules — triggers scripts on RPMsg char device add/remove events |
+| `rpmsg_create_channel.sh` | Creates RPMsg endpoint for a new channel using `rpmsg_export_ept` |
+| `rpmsg_add_ept_symlink.sh` | Creates user-friendly symlinks and sets device permissions on endpoint add |
+| `rpmsg_remove_ept_symlink.sh` | Removes symlinks when endpoint is removed |
+
+## How It Works
+
+When the remote processor starts and establishes an RPMsg channel, the kernel
+creates devices under `/sys/bus/rpmsg/devices/`. The udev rules trigger the
+scripts in the following order:
+
+```
+Remote processor boots
+    ↓
+RPMsg channel created → virtio0.rpmsg-openamp-demo-channel.-1.1024
+    ↓ udev ACTION==add
+rpmsg_create_channel.sh  → creates /dev/rpmsg0 via rpmsg_export_ept
+    ↓ udev ACTION==add (rpmsg0 endpoint)
+rpmsg_add_ept_symlink.sh → creates symlink
+    └── /dev/rpmsg_rpmsg-openamp-demo-channel.-1.1024.rpmsg0  → /dev/rpmsg0
+```
+
+On endpoint removal:
+```
+udev ACTION==remove (rpmsg0)
+    ↓
+rpmsg_remove_ept_symlink.sh → removes symlink
+
+
+```
+When removing the symlink, we need to find out which rpmsgX device is mapped
+to which symlink. The symlink name ends with `.rpmsgX`, so the removal script
+removes links matching `/dev/rpmsg_*.rpmsgX`.
+
+## Installation
+```bash
+# Install scripts and udev rule on a target system
+sudo make install
+
+# Reload udev rules
+sudo udevadm control --reload-rules
+sudo udevadm trigger
+```
+
+For staged installs used by Yocto and other build systems:
+
+```bash
+make DESTDIR=<image-root> install
+```
+
+The Makefile supports the standard install variables:
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `DESTDIR` | empty | Staging root used by package/image builds |
+| `prefix` | `/usr` | Install prefix |
+| `bindir` | `$(prefix)/bin` | Directory for helper scripts |
+| `udevdir` | `/etc/udev/rules.d` | Directory for udev rules |
+
+Example:
+
+```bash
+make DESTDIR="${D}" prefix=/usr udevdir=/lib/udev/rules.d install
+```
+
+## User Group Setup
+
+The udev rule assigns `/dev/rpmsg*` devices to the `rpmsg` group with
+`MODE="0660"` — only members of the `rpmsg` group can read and write the
+devices.
+
+```bash
+# Create rpmsg group, or optionally can be created by default during rootfs build
+sudo groupadd rpmsg
+
+# Add user to the group
+sudo usermod -aG rpmsg <username>
+
+# Apply group membership without logout
+newgrp rpmsg
+```
+
+> **Note:** Users must be members of the `rpmsg` group to access `/dev/rpmsg*`
+> devices. Changes to group membership require logout/login or `newgrp rpmsg`
+> to take effect.
+
+## Symlink Naming Convention
+
+| Symlink | Example | Points to |
+|---------|---------|-----------|
+| `rpmsg_ept_name.src.dst.rpmsg_dev` | `/dev/rpmsg_rpmsg-openamp-demo-channel.-1.1024.rpmsg0` | `/dev/rpmsg0` |
+
+## udev Rule Logic
+
+```
+SUBSYSTEM=="rpmsg", ACTION=="add"
+    │
+    ├── KERNEL=="virtio*.rpmsg_ctrl.0.0"  → SKIP (control device)
+    ├── KERNEL=="virtio*.rpmsg_ns.53.53"  → SKIP (namespace device)
+    ├── KERNEL=="rpmsg_ctrl[0-9]*"        → SKIP (ctrl device)
+    ├── KERNEL=="rpmsg*[0-9]*"            → rpmsg_add_ept_symlink.sh
+    └── default                           → rpmsg_create_channel.sh
+```
+
+## Requirements
+
+- Linux kernel 6.18 or later (`rpmsg_add_ept_symlink.sh`)
+- `rpmsg_export_ept` utility available in `/usr/bin`
+- udev running on the target system
+
+## Debugging
+
+# Monitor udev events
+udevadm monitor --udev --subsystem-match=rpmsg
+
+# Test rule match without executing
+udevadm test /sys/bus/rpmsg/devices/<device>
+
+# Check udev logs
+journalctl -u systemd-udevd -f
+```

examples/linux/rpmsg_udev_scripts/rpmsg_add_ept_symlink.sh

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+#!/bin/bash
+
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (C) 2026, Advanced Micro Devices, Inc.
+
+# valid for kernel 6.18 and later
+rpmsg_dev=$1
+max_tries=10
+retry_delay=0.1
+try=1
+
+# find control device for this channel
+# e.g. /sys/bus/rpmsg/devices/virtio0.rpmsg_ctrl.0.0/rpmsg/rpmsg_ctrl0/rpmsg0
+while [ "$try" -le "$max_tries" ]; do
+	rpmsg_dev_dir=$(find -L /sys/bus/rpmsg/devices/ -maxdepth 4 -name "$rpmsg_dev" 2>/dev/null)
+
+	if [ -n "$rpmsg_dev_dir" ] &&
+	   [ -r "$rpmsg_dev_dir/name" ] &&
+	   [ -r "$rpmsg_dev_dir/src" ] &&
+	   [ -r "$rpmsg_dev_dir/dst" ]; then
+		ept_name=$(cat "$rpmsg_dev_dir/name")  # e.g. rpmsg-openamp-demo-channel
+		ept_src=$(cat "$rpmsg_dev_dir/src")    # e.g. -1
+		ept_dst=$(cat "$rpmsg_dev_dir/dst")    # e.g. 1024
+
+		if [ -n "$ept_name" ] &&
+		   [ -n "$ept_src" ] &&
+		   [ -n "$ept_dst" ]; then
+			break
+		fi
+	fi
+
+	if [ "$try" -eq "$max_tries" ]; then
+		echo "failed to find ready sysfs attributes for $rpmsg_dev" >&2
+		exit 1
+	fi
+
+	sleep "$retry_delay"
+	try=$((try + 1))
+done
+
+ept_symlink_name="rpmsg_$ept_name.$ept_src.$ept_dst.$rpmsg_dev"
+ept_dev_path="/dev/$rpmsg_dev"
+ept_symlink_path="/dev/$ept_symlink_name"
+
+# create user mode accessible symlink
+
+# create symlink for apps to use. /dev/rpmsg_rpmsg-openamp-demo-channel.-1.1024.rpmsg0
+if [ -L "$ept_symlink_path" ]; then
+	if [ "$(readlink "$ept_symlink_path")" = "$ept_dev_path" ]; then
+		exit 0
+	fi
+
+	unlink "$ept_symlink_path"
+elif [ -e "$ept_symlink_path" ]; then
+	echo "$ept_symlink_path exists and is not a symlink" >&2
+	exit 1
+fi
+
+ln -s "$ept_dev_path" "$ept_symlink_path"

examples/linux/rpmsg_udev_scripts/rpmsg_create_channel.sh

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+#!/bin/bash
+
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (C) 2026, Advanced Micro Devices, Inc.
+
+# e.g. virtio0.rpmsg-openamp-demo-channel.-1.1024
+rpmsg_dev=$1
+
+# Split from the end so channel names can contain dots.
+ch_dest="${rpmsg_dev##*.}"
+rpmsg_dev_rest="${rpmsg_dev%.*}"
+ch_src="${rpmsg_dev_rest##*.}"
+rpmsg_dev_rest="${rpmsg_dev_rest%.*}"
+virtio_name="${rpmsg_dev_rest%%.*}"
+ch_name="${rpmsg_dev_rest#*.}"
+
+#find control device for this channel e.g. /dev/rpmsg_ctrl0
+rpmsg_ctrl_dev=$(ls "/sys/bus/rpmsg/devices/$rpmsg_dev/subsystem/devices/$virtio_name.rpmsg_ctrl.0.0/rpmsg/")
+
+# create endpoint for this channel e.g. /dev/rpmsg0
+res=$(rpmsg_export_ept "/dev/$rpmsg_ctrl_dev" "$ch_name" "$ch_src" "$ch_dest")

examples/linux/rpmsg_udev_scripts/rpmsg_remove_ept_symlink.sh

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+#!/bin/bash
+
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (C) 2026, Advanced Micro Devices, Inc.
+
+set -e
+set +x
+
+# e.g. "rpmsg0"
+rpmsg_dev=$1
+
+set +e
+
+# remove symlink ending with this rpmsg device name
+for rpmsg_dev_symlink in /dev/rpmsg_*."$rpmsg_dev"; do
+	[ -L "$rpmsg_dev_symlink" ] || continue
+	unlink "$rpmsg_dev_symlink" 2>/dev/null
+done