CV-Bowen opened a new pull request, #18248:
URL: https://github.com/apache/nuttx/pull/18248
## Summary
This PR improves shared memory buffer utilization in RPMSG communication by
allowing endpoints to release RX buffers early within their callback functions.
### Why is this change needed?
In the current RPMSG implementation, RX buffers are released after the
endpoint callback returns. This means the buffer remains occupied during the
entire callback execution, even if the callback has already copied the data to
its own private buffer. In scenarios with limited shared memory or
high-frequency message exchanges, this can lead to buffer exhaustion and
communication stalls.
### What does this PR do?
1. **OpenAMP patch (Commit 1)**: Adds support for early RX buffer release in
`rpmsg_virtio`:
- Introduces `RPMSG_SUCCESS_BUFFER_RELEASED` return code (-1000) to
indicate the buffer has been released by the callback
- Modifies `rpmsg_virtio_rx_callback()` to skip buffer release if
callback returns `RPMSG_SUCCESS_BUFFER_RELEASED`
- Updates `rpmsg_virtio_ns_callback()` (name service) to copy the message
to a local variable and release the RX buffer immediately, then return
`RPMSG_SUCCESS_BUFFER_RELEASED`
2. **NuttX rpmsg_port driver (Commit 2)**: Extends the same early release
support to `rpmsg_port`:
- Updates `rpmsg_port_rx_callback()` to check for
`RPMSG_SUCCESS_BUFFER_RELEASED` return code
- Skips automatic buffer release when callback indicates it has already
released the buffer
### Files Changed
| File | Changes |
|------|---------|
| `openamp/0016-lib-rpmsg_virtio-support-release-the-name-service-me.patch`
| New patch file for OpenAMP |
| `openamp/open-amp.cmake` | Add new patch to CMake build |
| `openamp/open-amp.defs` | Add new patch to Make build |
| `drivers/rpmsg/rpmsg_port.c` | Support early buffer release in rpmsg_port |
## Impact
- **Stability**: No impact. The change is backward compatible - existing
callbacks that don't use early release continue to work as before.
- **Compatibility**: Fully backward compatible. Callbacks can optionally
return `RPMSG_SUCCESS_BUFFER_RELEASED` to indicate early release.
- **Performance**: Improves shared memory utilization, especially beneficial
for:
- Systems with limited shared memory
- High-frequency message exchanges
- Name service operations (now releases buffer immediately after copying)
## Testing
### Build Verification
```bash
# Build for QEMU ARMv8-A dual-core configuration
cmake -B cmake_out/v8a_server -DBOARD_CONFIG=qemu-armv8a:rpserver -GNinja
cmake --build cmake_out/v8a_server
cmake -B cmake_out/v8a_proxy -DBOARD_CONFIG=qemu-armv8a:rpproxy -GNinja
cmake --build cmake_out/v8a_proxy
```
### Runtime Testing
Tested on QEMU ARMv8-A with dual-core RPMSG communication via ivshmem:
**Terminal 1 (Server):**
```bash
qemu-system-aarch64 -cpu cortex-a53 -nographic \
-machine virt,virtualization=on,gic-version=3 \
-chardev stdio,id=con,mux=on -serial chardev:con \
-object
memory-backend-file,discard-data=on,id=shmmem-shmem0,mem-path=/dev/shm/my_shmem0,size=4194304,share=yes
\
-device ivshmem-plain,id=shmem0,memdev=shmmem-shmem0,addr=0xb \
-device virtio-serial-device,bus=virtio-mmio-bus.0 \
-chardev socket,path=/tmp/rpmsg_port_uart_socket,server=on,wait=off,id=foo \
-device virtconsole,chardev=foo \
-mon chardev=con,mode=readline -kernel ./nuttx/cmake_out/v8a_server/nuttx \
-gdb tcp::7775
```
**Terminal 2 (Proxy):**
```bash
qemu-system-aarch64 -cpu cortex-a53 -nographic \
-machine virt,virtualization=on,gic-version=3 \
-chardev stdio,id=con,mux=on -serial chardev:con \
-object
memory-backend-file,discard-data=on,id=shmmem-shmem0,mem-path=/dev/shm/my_shmem0,size=4194304,share=yes
\
-device ivshmem-plain,id=shmem0,memdev=shmmem-shmem0,addr=0xb \
-device virtio-serial-device,bus=virtio-mmio-bus.0 \
-chardev socket,path=/tmp/rpmsg_port_uart_socket,server=off,id=foo \
-device virtconsole,chardev=foo \
-mon chardev=con,mode=readline -kernel ./nuttx/cmake_out/v8a_proxy/nuttx \
-gdb tcp::7776
```
**Test Results:**
```c
❯ qemu-system-aarch64 -cpu cortex-a53 -nographic \
-machine virt,virtualization=on,gic-version=3 \
-chardev stdio,id=con,mux=on -serial chardev:con \
-object
memory-backend-file,discard-data=on,id=shmmem-shmem0,mem-path=/dev/shm/my_shmem0,size\
-device ivshmem-plain,id=shmem0,memdev=shmmem-shmem0,addr=0xb \
-device virtio-serial-device,bus=virtio-mmio-bus.0 \
-chardev socket,path=/tmp/rpmsg_port_uart_socket,server=on,wait=off,id=foo \
-device virtconsole,chardev=foo \
-mon chardev=con,mode=readline -kernel ./nuttx/cmake_out/v8a_server/nuttx \
-gdb tcp::7775
[ 0.000000] [ 0] [ INFO] [server] pci_register_rptun_ivshmem_driver:
Register ivshmem dri1
[ 0.000000] [ 3] [ INFO] [server] pci_scan_bus: pci_scan_bus for bus 0
[ 0.000000] [ 3] [ INFO] [server] pci_scan_bus: class = 00000600,
hdr_type = 00000000
[ 0.000000] [ 3] [ INFO] [server] pci_scan_bus: 00:00 [1b36:0008]
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar0 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar1 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar2 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar3 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar4 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar5 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_scan_bus: class = 00000200,
hdr_type = 00000000
[ 0.000000] [ 3] [ INFO] [server] pci_scan_bus: 00:08 [1af4:1000]
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar0:
mask64=fffffffe 32bytes
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar1:
mask64=fffffff0 4096bytes
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar2 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar3 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar4:
mask64=fffffffffffffff0 16384bs
[ 0.000000] [ 3] [ INFO] [server] pci_scan_bus: class = 00000500,
hdr_type = 00000000
[ 0.000000] [ 3] [ INFO] [server] pci_scan_bus: 00:58 [1af4:1110]
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar0:
mask64=fffffff0 256bytes
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar1 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar2:
mask64=fffffffffffffff0 419430s
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar4 set bad mask
[ 0.000000] [ 3] [ INFO] [server] pci_setup_device: pbar5 set bad mask
[ 0.000000] [ 3] [ INFO] [server] ivshmem_probe: shmem addr=0x10400000
size=4194304 reg=00
[ 0.000000] [ 3] [ INFO] [server] rptun_ivshmem_probe: shmem
addr=0x10400000 size=4194304
NuttShell (NSH) NuttX-12.10.0
server>
server>
server> [ 0.000000] [ 0] [ INFO] [proxy]
pci_register_rptun_ivshmem_driver: Register ivsh0
[ 0.000000] [ 3] [ INFO] [proxy] pci_scan_bus: pci_scan_bus for bus 0
[ 0.000000] [ 3] [ INFO] [proxy] pci_scan_bus: class = 00000600,
hdr_type = 00000000
[ 0.000000] [ 3] [ INFO] [proxy] pci_scan_bus: 00:00 [1b36:0008]
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar0 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar1 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar2 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar3 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar4 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar5 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_scan_bus: class = 00000200,
hdr_type = 00000000
[ 0.000000] [ 3] [ INFO] [proxy] pci_scan_bus: 00:08 [1af4:1000]
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar0:
mask64=fffffffe 32bytes
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar1:
mask64=fffffff0 4096bytes
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar2 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar3 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar4:
mask64=fffffffffffffff0 16384bys
[ 0.000000] [ 3] [ INFO] [proxy] pci_scan_bus: class = 00000500,
hdr_type = 00000000
[ 0.000000] [ 3] [ INFO] [proxy] pci_scan_bus: 00:58 [1af4:1110]
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar0:
mask64=fffffff0 256bytes
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar1 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar2:
mask64=fffffffffffffff0 4194304s
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar4 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] pci_setup_device: pbar5 set bad mask
[ 0.000000] [ 3] [ INFO] [proxy] ivshmem_probe: shmem addr=0x10400000
size=4194304 reg=0x0
[ 0.000000] [ 3] [ INFO] [proxy] rptun_ivshmem_probe: shmem
addr=0x10400000 size=4194304
[ 0.000000] [ 3] [ INFO] [proxy] rptun_ivshmem_probe: Start the wdog
server>
server>
server>
server> ps
TID PID PPID PRI POLICY TYPE NPX STATE EVENT SIGMASK
STACK USED
0 0 0 0 FIFO Kthread - Ready
0000000000000000 0008144 000179k
1 0 0 192 FIFO Kthread - Waiting Semaphore
0000000000000000 0008080 0001320
2 0 0 100 FIFO Kthread - Waiting Semaphore
0000000000000000 0008080 0001320
5 0 0 224 FIFO Kthread - Waiting Semaphore
0000000000000000 0008080 0002088
6 0 0 224 FIFO Kthread - Waiting Event
0000000000000000 0008080 0001968
7 7 0 100 FIFO Task - Running
0000000000000000 0008112 000417n
8 0 0 224 FIFO Kthread - Waiting Semaphore
0000000000000000 0008080 0001878
server> rpmsg dump all
[ 0.000000] [ 7] [ EMERG] [server] Local: server Remote: proxy Headrx 7
[ 0.000000] [ 7] [ EMERG] [server] Dump rpmsg info between cpu (master:
yes)server <==> pr:
[ 0.000000] [ 7] [ EMERG] [server] rpmsg vq RX:
[ 0.000000] [ 7] [ EMERG] [server] rpmsg vq TX:
[ 0.000000] [ 7] [ EMERG] [server] rpmsg ept list:
[ 0.000000] [ 7] [ EMERG] [server] ept NS
[ 0.000000] [ 7] [ EMERG] [server] ept rpmsg-sensor
[ 0.000000] [ 7] [ EMERG] [server] ept rpmsg-ping
[ 0.000000] [ 7] [ EMERG] [server] ept rpmsg-syslog
[ 0.000000] [ 7] [ EMERG] [server] rpmsg buffer list:
[ 0.000000] [ 7] [ EMERG] [server] RX buffer, total 8, pending 0
[ 0.000000] [ 7] [ EMERG] [server] TX buffer, total 8, pending 0
[ 0.000000] [ 7] [ EMERG] [server] Remote: proxy2 state: 1
[ 0.000000] [ 7] [ EMERG] [server] ept NS
[ 0.000000] [ 7] [ EMERG] [server] ept rpmsg-sensor
[ 0.000000] [ 7] [ EMERG] [server] ept rpmsg-ping
[ 0.000000] [ 7] [ EMERG] [server] rpmsg_port queue RX: {used: 0, avail:
8}
[ 0.000000] [ 7] [ EMERG] [server] rpmsg buffer list:
[ 0.000000] [ 7] [ EMERG] [server] rpmsg_port queue TX: {used: 0, avail:
8}
[ 0.000000] [ 7] [ EMERG] [server] rpmsg buffer list:
[ 0.000000] [ 7] [ ALERT] [server] sched_dumpstack: backtrace| 5:
0x00000000402a8500 0x0004
[ 0.000000] [ 7] [ ALERT] [server] sched_dumpstack: backtrace| 5:
0x00000000402ace74
[ 0.000000] [ 7] [ ALERT] [server] sched_dumpstack: backtrace| 6:
0x00000000402a8920 0x0004
server> rpmsg ping all 1 1 1 1
[ 0.000000] [ 7] [ EMERG] [server] ping times: 1
[ 0.000000] [ 7] [ EMERG] [server] buffer_len: 1520, send_len: 17
[ 0.000000] [ 7] [ EMERG] [server] avg: 0 s, 19725360 ns
[ 0.000000] [ 7] [ EMERG] [server] min: 0 s, 19725360 ns
[ 0.000000] [ 7] [ EMERG] [server] max: 0 s, 19725360 ns
[ 0.000000] [ 7] [ EMERG] [server] rate: 0.006894 Mbits/sec
[ 0.000000] [ 7] [ EMERG] [server] ping times: 1
[ 0.000000] [ 7] [ EMERG] [server] buffer_len: 2024, send_len: 17
[ 0.000000] [ 7] [ EMERG] [server] avg: 0 s, 13472656 ns
[ 0.000000] [ 7] [ EMERG] [server] min: 0 s, 13472656 ns
[ 0.000000] [ 7] [ EMERG] [server] max: 0 s, 13472656 ns
[ 0.000000] [ 7] [ EMERG] [server] rate: 0.010094 Mbits/sec
server> uname -a
NuttX server 12.10.0 8a84813cd59 Jan 28 2026 21:59:29 arm64 qemu-armv8a
server>
```
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