[PATCH 5/7] drivers: greybus: Add software SVC implementation

A Greybus network requires an SVC (Supervisory Controller) to bring
interfaces up, assign device IDs and connect CPorts to the AP. On a
UniPro network the SVC is a real entity on the bus, but transports that
merely carry Greybus messages - a UART, an I2C bus, a network link -
have no such entity, so every host driver for those transports ends up
open-coding an SVC emulation of its own.

Add gb-softsvc, a Rust implementation of the SVC that lives in the
kernel and registers itself as a Greybus host device. It answers the
SVC-side operations the core expects during interface bring-up and
teardown.

Host drivers use it through a small in-kernel interface. A driver
implements the NodeOps trait to send data towards its node and then
calls module_insert() to announce a new node, submit_message() to hand
incoming Greybus messages back to the core, and module_remove() on
disconnect. Interface IDs are allocated by the SVC and returned from
module_insert().

Connection create/destroy and interface activate/resume currently just
acknowledge the request; callbacks into NodeOps can be added later if
transports need to act on them.

gb_softsvc_exports.c exports the Rust symbols for dependent modules, as
the build system does not yet support Rust cross-module dependencies
natively. This hack is taken from nova-core [0].

[0]: https://lore.kernel.org/all/[email protected]/

Signed-off-by: Ayush Singh <[email protected]>
---
 MAINTAINERS                          |   6 +
 drivers/greybus/Kconfig              |  12 +
 drivers/greybus/Makefile             |   2 +
 drivers/greybus/gb_softsvc.rs        | 472 +++++++++++++++++++++++++++++++++++
 drivers/greybus/gb_softsvc_exports.c |  15 ++
 5 files changed, 507 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 80247a031353..3ba56cdbf056 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11328,6 +11328,12 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/net/ti,cc1352p7.yaml
 F:	drivers/greybus/gb-beagleplay.c
 
+GREYBUS SOFTSVC DRIVERS
+M:	Ayush Singh <[email protected]>
+L:	[email protected] (moderated for non-subscribers)
+S:	Maintained
+F:	drivers/greybus/gb_softsvc.rs
+
 GREYBUS SUBSYSTEM
 M:	Johan Hovold <[email protected]>
 M:	Alex Elder <[email protected]>
diff --git a/drivers/greybus/Kconfig b/drivers/greybus/Kconfig
index c3f056d28b01..30bc491841e1 100644
--- a/drivers/greybus/Kconfig
+++ b/drivers/greybus/Kconfig
@@ -41,5 +41,17 @@ config GREYBUS_ES2
 	  To compile this code as a module, choose M here: the module
 	  will be called gb-es2.ko
 
+config GREYBUS_SOFTSVC
+	tristate "Greybus software SVC"
+	depends on RUST
+	help
+	  Select this option to enable a software implementation of the
+	  Greybus SVC (Supervisory Controller) running in the kernel. It can
+	  be used by host drivers that talk to a Greybus network which does
+	  not provide an SVC of its own.
+
+	  To compile this code as a module, choose M here: the module
+	  will be called gb-softsvc.ko
+
 endif	# GREYBUS
 
diff --git a/drivers/greybus/Makefile b/drivers/greybus/Makefile
index d986e94f8897..e6f594128802 100644
--- a/drivers/greybus/Makefile
+++ b/drivers/greybus/Makefile
@@ -25,4 +25,6 @@ gb-es2-y := es2.o
 
 obj-$(CONFIG_GREYBUS_ES2)	+= gb-es2.o
 
+obj-$(CONFIG_GREYBUS_SOFTSVC)	+= gb-softsvc.o
+gb-softsvc-y			+= gb_softsvc.o gb_softsvc_exports.o
 
diff --git a/drivers/greybus/gb_softsvc.rs b/drivers/greybus/gb_softsvc.rs
new file mode 100644
index 000000000000..0d125a1a2cc8
--- /dev/null
+++ b/drivers/greybus/gb_softsvc.rs
@@ -0,0 +1,472 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Greybus software SVC.
+//!
+//! A Greybus network needs an SVC to bring interfaces up and to connect their CPorts to the AP.
+//! Transports that carry Greybus without one - a UART or an I2C bus rather than a UniPro network -
+//! have to provide it themselves.
+//!
+//! This module implements that SVC in software.
+
+use kernel::error::code;
+use kernel::greybus::{self, hd, protocols, CPORT_ID_MAX, GB_OPERATION_SIZE_MAX};
+use kernel::id_pool::IdPool;
+use kernel::sync::{Arc, Mutex, SpinLock};
+use kernel::transmute::AsBytes;
+use kernel::{c_str, faux, prelude::*, sync::aref::ARef};
+use kernel::{new_mutex, new_spinlock};
+use pin_init::init_array_from_fn;
+
+const SVC_VERSION_MAJOR: u8 = 0;
+const SVC_VERSION_MINOR: u8 = 1;
+const ENDO_ID: u16 = u16::from_le(0x4755);
+const AP_INF_ID: u8 = 0;
+
+const MAX_INTF_ID: u8 = u8::MAX;
+const INTF_ID_START: u8 = 1;
+const INTF_MAP_LEN: usize = (MAX_INTF_ID - INTF_ID_START) as usize;
+
+#[repr(C, packed)]
+struct Msg<P> {
+    hdr: protocols::GbOperationMsgHdr,
+    payload: P,
+}
+
+// SAFETY: `Msg` is a POD type with no padding and no interior mutability.
+unsafe impl<P> kernel::transmute::AsBytes for Msg<P> {}
+
+impl<P> Msg<P> {
+    const GB_SIZE: u16 = size_of::<Self>() as u16;
+
+    /// Builds a request of type `ty`.
+    ///
+    /// An `operation_id` of zero marks a unidirectional request, for which the AP sends no
+    /// response.
+    const fn request(operation_id: u16, ty: u8, payload: P) -> Self {
+        Self {
+            hdr: protocols::GbOperationMsgHdr::new(Self::GB_SIZE, operation_id, ty, 0),
+            payload,
+        }
+    }
+
+    /// Builds the response to `request`, carrying `result`.
+    const fn response(request: &protocols::GbOperationMsgHdr, result: u8, payload: P) -> Self {
+        Self {
+            hdr: protocols::GbOperationMsgHdr::new(
+                Self::GB_SIZE,
+                request.operation_id(),
+                request.msg_type() | protocols::MESSAGE_TYPE_RESPONSE,
+                result,
+            ),
+            payload,
+        }
+    }
+}
+
+const _: () = assert!(size_of::<Msg<()>>() == size_of::<protocols::GbOperationMsgHdr>());
+
+module! {
+    type: GreybusSoftSvc,
+    name: "gb_softsvc",
+    authors: ["Ayush Singh <[email protected]>"],
+    description: "Greybus software SVC implementation",
+    license: "GPL",
+}
+
+kernel::sync::global_lock! {
+    unsafe(uninit) static GLOBAL_STATE: Mutex<Option<GlobalState>> = None;
+}
+
+struct GlobalState {
+    svc: Arc<Svc>,
+    gb_hd: ARef<hd::Device>,
+}
+
+impl GlobalState {
+    fn new(svc: Arc<Svc>, gb_hd: ARef<hd::Device>) -> Self {
+        Self { svc, gb_hd }
+    }
+}
+
+#[pin_data]
+struct Svc {
+    #[pin]
+    svc_operation_id: SpinLock<IdPool>,
+    // Pos 0 = INTF_ID_START
+    #[pin]
+    intf_map: Mutex<[Option<Arc<dyn InterfaceOps>>; INTF_MAP_LEN]>,
+}
+
+impl Svc {
+    fn new() -> impl PinInit<Self, Error> {
+        pin_init!(Self {
+            intf_map <- new_mutex!(init_array_from_fn(|_| None)),
+            svc_operation_id <- new_spinlock!(IdPool::with_capacity(u16::MAX.into(), GFP_KERNEL)?)
+        }? Error)
+    }
+
+    fn new_operation_id(&self) -> Result<u16> {
+        let mut ida = self.svc_operation_id.lock();
+        let res = ida.find_unused_id(1).ok_or(code::EOVERFLOW)?.acquire() as u16;
+
+        Ok(res)
+    }
+
+    fn release_operation_id(&self, id: u16) {
+        let mut ida = self.svc_operation_id.lock();
+        ida.release_id(id as usize);
+    }
+
+    fn map_insert(&self, intfs: &[Arc<dyn InterfaceOps>]) -> Result<u8> {
+        fn inner(
+            intf_map: &[Option<Arc<dyn InterfaceOps>>; INTF_MAP_LEN],
+            count: usize,
+        ) -> Result<u8> {
+            for (id, window) in intf_map.windows(count).enumerate() {
+                if window.iter().all(|x| x.is_none()) {
+                    return Ok(id as u8);
+                }
+            }
+
+            Err(code::EOVERFLOW)
+        }
+
+        let mut guard = self.intf_map.lock();
+
+        let pos = inner(&guard, intfs.len())?;
+        for (i, intf) in intfs.iter().cloned().enumerate() {
+            guard[usize::from(pos) + i] = Some(intf);
+        }
+
+        Ok(pos + INTF_ID_START)
+    }
+
+    fn map_remove(&self, primary_id: u8, intf_count: u8) {
+        let id = primary_id - INTF_ID_START;
+        let mut guard = self.intf_map.lock();
+
+        for i in 0..intf_count {
+            let _ = guard[usize::from(id + i)].take();
+        }
+    }
+
+    fn intf_by_id(&self, id: u8) -> Result<Arc<dyn InterfaceOps>> {
+        let id = id - INTF_ID_START;
+        let guard = self.intf_map.lock();
+
+        guard
+            .get(usize::from(id))
+            .ok_or(code::ENODEV)?
+            .as_ref()
+            .ok_or(code::ENODEV)
+            .cloned()
+    }
+
+    fn send_request<P>(&self, hd: &hd::Device, ty: u8, payload: P) -> Result<()> {
+        let msg = Msg::request(self.new_operation_id()?, ty, payload);
+        hd.data_rcvd(protocols::GB_SVC_CPORT_ID, msg.as_bytes());
+        Ok(())
+    }
+
+    fn module_insert(&self, hd: &hd::Device, intfs: &[Arc<dyn InterfaceOps>]) -> Result<u8> {
+        let intf_id = self.map_insert(intfs)?;
+        let payload = protocols::GbSvcModuleInsertedRequest::new(intf_id, 1, 0);
+        self.send_request(hd, protocols::GB_SVC_TYPE_MODULE_INSERTED, payload)?;
+
+        Ok(intf_id)
+    }
+
+    fn module_remove(&self, hd: &hd::Device, intf_id: u8, intf_count: u8) -> Result<()> {
+        self.map_remove(intf_id, intf_count);
+        let payload = protocols::GbSvcModuleRemovedRequest::new(intf_id);
+        self.send_request(hd, protocols::GB_SVC_TYPE_MODULE_REMOVED, payload)?;
+
+        Ok(())
+    }
+
+    fn send_version(&self, hd: &hd::Device) -> Result<()> {
+        dev_info!(hd.as_ref(), "Sending SVC version request");
+
+        let payload = protocols::GbSvcVersionRequest::new(SVC_VERSION_MAJOR, SVC_VERSION_MINOR);
+        self.send_request(hd, protocols::GB_SVC_TYPE_PROTOCOL_VERSION, payload)?;
+
+        Ok(())
+    }
+
+    fn send_svc_hello(&self, hd: &hd::Device) -> Result<()> {
+        dev_info!(hd.as_ref(), "Sending SVC Hello request");
+
+        let payload = protocols::GbSvcHelloRequest::new(ENDO_ID, AP_INF_ID);
+        self.send_request(hd, protocols::GB_SVC_TYPE_SVC_HELLO, payload)?;
+
+        Ok(())
+    }
+
+    fn send_response<P>(&self, hd: &hd::Device, msg: &protocols::GbOperationMsgHdr, payload: P) {
+        let msg = Msg::response(msg, 0, payload);
+        hd.data_rcvd(protocols::GB_SVC_CPORT_ID, msg.as_bytes());
+    }
+
+    fn intf_set_pwrm(&self, hd: &hd::Device, msg: &greybus::Message) -> Result<()> {
+        let req_msg: &protocols::GbSvcIntfSetPwrmRequest = msg.payload().ok_or(code::EINVAL)?;
+        let result_code = if req_msg.tx_mode() == protocols::GB_SVC_UNIPRO_HIBERNATE_MODE
+            && req_msg.rx_mode() == protocols::GB_SVC_UNIPRO_HIBERNATE_MODE
+        {
+            protocols::GB_SVC_SETPWRM_PWR_OK
+        } else {
+            protocols::GB_SVC_SETPWRM_PWR_LOCAL
+        };
+
+        let payload = protocols::GbSvcIntfSetPwrmResponse::new(result_code);
+        self.send_response(hd, msg.header(), payload);
+
+        Ok(())
+    }
+
+    fn dme_peer_get(&self, hd: &hd::Device, hdr: &protocols::GbOperationMsgHdr) {
+        let payload = protocols::GbSvcDmePeerGetResponse::new(0, u32::from_le(0x0126));
+        self.send_response(hd, hdr, payload);
+    }
+
+    fn dme_peer_set(&self, hd: &hd::Device, hdr: &protocols::GbOperationMsgHdr) {
+        let payload = protocols::GbSvcDmePeerSetResponse::new(0);
+        self.send_response(hd, hdr, payload);
+    }
+
+    fn pwrmon_rail_count_get(&self, hd: &hd::Device, hdr: &protocols::GbOperationMsgHdr) {
+        let payload = protocols::GbSvcPwrmonRailCountGetResponse::new(0);
+        self.send_response(hd, hdr, payload);
+    }
+
+    fn intf_vsys_enable_disable(&self, hd: &hd::Device, hdr: &protocols::GbOperationMsgHdr) {
+        let payload = protocols::GbSvcIntfVsysResponse::new(protocols::GB_SVC_INTF_VSYS_OK);
+        self.send_response(hd, hdr, payload);
+    }
+
+    fn intf_refclk_enable_disable(&self, hd: &hd::Device, hdr: &protocols::GbOperationMsgHdr) {
+        let payload = protocols::GbSvcIntfRefclkResponse::new(protocols::GB_SVC_INTF_VSYS_OK);
+        self.send_response(hd, hdr, payload);
+    }
+
+    fn intf_unipro_enable_disable(&self, hd: &hd::Device, hdr: &protocols::GbOperationMsgHdr) {
+        let payload = protocols::GbSvcIntfUniproResponse::new(protocols::GB_SVC_INTF_UNIPRO_OK);
+        self.send_response(hd, hdr, payload);
+    }
+
+    fn intf_activate(&self, hd: &hd::Device, msg: &greybus::Message) {
+        let payload = protocols::GbSvcIntfActivateResponse::new(
+            protocols::GB_SVC_OP_SUCCESS,
+            protocols::GB_SVC_INTF_TYPE_GREYBUS,
+        );
+
+        // TODO: Maybe call a callback?
+
+        self.send_response(hd, msg.header(), payload);
+    }
+
+    fn intf_resume(&self, hd: &hd::Device, msg: &greybus::Message) {
+        let payload = protocols::GbSvcIntfResumeResponse::new(protocols::GB_SVC_OP_SUCCESS);
+
+        // TODO: Maybe call a callback?
+
+        self.send_response(hd, msg.header(), payload);
+    }
+
+    fn conn_create(&self, hd: &hd::Device, msg: &greybus::Message) -> Result<()> {
+        // TODO: Evaluate if we need to add callback to NodeOps
+        self.send_response(hd, msg.header(), ());
+
+        Ok(())
+    }
+
+    fn conn_destroy(&self, hd: &hd::Device, msg: &greybus::Message) -> Result<()> {
+        // TODO: Evaluate if we need to add callback to NodeOps
+        self.send_response(hd, msg.header(), ());
+
+        Ok(())
+    }
+
+    fn handler(&self, msg: &greybus::Message) -> Result<()> {
+        let hdr = msg.header();
+        let hd = msg.operation().connection().host_device();
+
+        if hdr.is_response() {
+            self.release_operation_id(hdr.operation_id());
+        }
+
+        match (hdr.is_response(), hdr.request_type()) {
+            (
+                false,
+                protocols::GB_SVC_TYPE_INTF_DEVICE_ID
+                | protocols::GB_SVC_TYPE_ROUTE_CREATE
+                | protocols::GB_SVC_TYPE_ROUTE_DESTROY
+                | protocols::GB_SVC_TYPE_PING,
+            ) => self.send_response(hd, hdr, ()),
+            (false, protocols::GB_SVC_TYPE_CONN_CREATE) => self.conn_create(hd, msg)?,
+            (false, protocols::GB_SVC_TYPE_CONN_DESTROY) => self.conn_destroy(hd, msg)?,
+            (false, protocols::GB_SVC_TYPE_DME_PEER_GET) => self.dme_peer_get(hd, hdr),
+            (false, protocols::GB_SVC_TYPE_DME_PEER_SET) => self.dme_peer_set(hd, hdr),
+            (false, protocols::GB_SVC_TYPE_INTF_SET_PWRM) => self.intf_set_pwrm(hd, msg)?,
+            (false, protocols::GB_SVC_TYPE_PWRMON_RAIL_COUNT_GET) => {
+                self.pwrmon_rail_count_get(hd, hdr)
+            }
+            (
+                false,
+                protocols::GB_SVC_TYPE_INTF_VSYS_ENABLE | protocols::GB_SVC_TYPE_INTF_VSYS_DISABLE,
+            ) => self.intf_vsys_enable_disable(hd, hdr),
+            (
+                false,
+                protocols::GB_SVC_TYPE_INTF_REFCLK_ENABLE
+                | protocols::GB_SVC_TYPE_INTF_REFCLK_DISABLE,
+            ) => self.intf_refclk_enable_disable(hd, hdr),
+            (
+                false,
+                protocols::GB_SVC_TYPE_INTF_UNIPRO_ENABLE
+                | protocols::GB_SVC_TYPE_INTF_UNIPRO_DISABLE,
+            ) => self.intf_unipro_enable_disable(hd, hdr),
+            (false, protocols::GB_SVC_TYPE_INTF_ACTIVATE) => self.intf_activate(hd, msg),
+            (false, protocols::GB_SVC_TYPE_INTF_RESUME) => self.intf_resume(hd, msg),
+            (true, protocols::GB_SVC_TYPE_PROTOCOL_VERSION) => self.send_svc_hello(hd)?,
+            (
+                true,
+                protocols::GB_SVC_TYPE_MODULE_INSERTED
+                | protocols::GB_SVC_TYPE_SVC_HELLO
+                | protocols::GB_SVC_TYPE_MODULE_REMOVED,
+            ) => {}
+            _ => return Err(code::ENOTSUPP),
+        };
+
+        Ok(())
+    }
+}
+
+struct GbHdDriver(Arc<Svc>);
+
+impl GbHdDriver {
+    fn message_send_inner(&self, dest_cport_id: u16, msg: &greybus::Message) -> Result {
+        if dest_cport_id == protocols::GB_SVC_CPORT_ID {
+            self.0.handler(msg)
+        } else {
+            let conn = msg.operation().connection();
+            let intf = self.0.intf_by_id(conn.interface().unwrap().id())?;
+
+            let mut buf = KVec::with_capacity(msg.header().size().into(), GFP_KERNEL)?;
+
+            buf.extend_from_slice(msg.header().as_bytes(), GFP_KERNEL)?;
+            buf.extend_from_slice(msg.payload_bytes(), GFP_KERNEL)?;
+
+            intf.write(&buf, conn.intf_cport_id())
+        }
+    }
+}
+
+#[vtable]
+impl hd::HdDriver for GbHdDriver {
+    fn message_send(data: &Self, dest_cport_id: u16, msg: greybus::Message) -> Result {
+        let res = data.message_send_inner(dest_cport_id, &msg);
+        msg.sent(0);
+
+        res
+    }
+
+    fn message_cancel(_msg: greybus::Message) {}
+}
+
+struct GreybusSoftSvc {
+    _hd: hd::Registration<GbHdDriver>,
+    _faux: faux::Registration,
+}
+
+impl kernel::Module for GreybusSoftSvc {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        pr_info!("gb_softsvc (init)\n");
+
+        // SAFETY: This runs once at module init, before anything else can reach `GLOBAL_STATE`.
+        unsafe { GLOBAL_STATE.init() };
+
+        let faux = faux::Registration::new(c_str!("gb-softsvc"), None)?;
+        let svc = Arc::pin_init(Svc::new(), GFP_KERNEL)?;
+        let data = GbHdDriver(svc.clone());
+
+        let dev = faux.as_ref().as_ref();
+        let hd = hd::Registration::new(dev, GB_OPERATION_SIZE_MAX, CPORT_ID_MAX + 1, Ok(data))?;
+
+        let global_state = GlobalState::new(svc.clone(), hd.as_ref().into());
+        let _ = GLOBAL_STATE.lock().replace(global_state);
+
+        svc.send_version(hd.as_ref())?;
+
+        Ok(GreybusSoftSvc {
+            _hd: hd,
+            _faux: faux,
+        })
+    }
+}
+
+impl Drop for GreybusSoftSvc {
+    fn drop(&mut self) {
+        let _ = GLOBAL_STATE.lock().take();
+        pr_info!("gb_softsvc (exit)\n");
+    }
+}
+
+/// The operations a Greybus interface provides.
+///
+/// A node is whatever sits behind an interface — a real transport, an in-kernel emulation, or
+/// anything else that can accept Greybus traffic. This module does not care which.
+pub trait InterfaceOps: Send + Sync {
+    /// Delivers `data` to the node's `cport`.
+    fn write(&self, data: &[u8], cport: u16) -> Result<()>;
+}
+
+/// A module attached to the Greybus network.
+pub struct Module {
+    id: u8,
+    intf_count: u8,
+    gb_hd: ARef<hd::Device>,
+    svc: Arc<Svc>,
+}
+
+impl Module {
+    /// Attaches `node` as a new module and returns the interface id assigned to it.
+    pub fn new(intfs: &[Arc<dyn InterfaceOps>]) -> Result<Self> {
+        let Ok(intf_count) = u8::try_from(intfs.len()) else {
+            return Err(code::E2BIG);
+        };
+
+        let guard = GLOBAL_STATE.lock();
+        let state = guard.as_ref().ok_or(code::EAGAIN)?;
+        let id = state.svc.module_insert(&state.gb_hd, intfs)?;
+
+        Ok(Self {
+            id,
+            intf_count,
+            gb_hd: state.gb_hd.clone(),
+            svc: state.svc.clone(),
+        })
+    }
+
+    /// Delivers `msg`, received from interface `id` on its `cport`, to the Greybus core.
+    ///
+    /// `cport` is the interface-side CPort id.
+    ///
+    /// Fails with `EINVAL` if no connection is bound to that pair, or `EAGAIN` if the
+    /// host device has not been brought up yet.
+    pub fn submit_message(&self, cport: u16, msg: &[u8]) -> Result<()> {
+        let intf = self
+            .gb_hd
+            .find_connection_by_intf(self.id, cport)
+            .ok_or(code::EINVAL)?;
+        self.gb_hd.data_rcvd(intf.hd_cport_id(), msg);
+
+        Ok(())
+    }
+}
+
+impl Drop for Module {
+    fn drop(&mut self) {
+        let _ = self
+            .svc
+            .module_remove(&self.gb_hd, self.id, self.intf_count);
+    }
+}
diff --git a/drivers/greybus/gb_softsvc_exports.c b/drivers/greybus/gb_softsvc_exports.c
new file mode 100644
index 000000000000..38b99c4de6ee
--- /dev/null
+++ b/drivers/greybus/gb_softsvc_exports.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+
+/*
+ * Exports Rust symbols from the `nova_core` crate for use by dependent modules.
+ *
+ * This is a workaround until the build system supports Rust cross-module
+ * dependencies natively.
+ */
+
+#include <linux/export.h>
+
+#define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym)
+
+#include "exports_gb_softsvc_generated.h"

-- 
2.55.0