[PATCH v2 6/8] rust: pci: add bus callback sriov_configure(), to control SR-IOV from sysfs

[Zhi Wang <zhiw@nvidia.com>]

From: Peter Colberg <pcolberg@redhat.com>

Add an optional bus callback sriov_configure() to pci::Driver trait,
using the vtable attribute to query if the driver implements the
callback. The callback is invoked when a user-space application
writes the number of VFs to the sysfs file `sriov_numvfs` to
enable SR-IOV, or zero to disable SR-IOV for a PCI device.

Invoke the callback with zero before PF unbind so drivers can release
their SR-IOV resources, including runtime-PM references. Disable any
remaining VFs before releasing the PF driver data.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Peter Colberg <pcolberg@redhat.com>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 rust/kernel/pci.rs | 65 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index db0554f14afc..cb3ed2207075 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -84,6 +84,10 @@ unsafe fn register(
             (*pdrv.get()).probe = Some(Self::probe_callback);
             (*pdrv.get()).remove = Some(Self::remove_callback);
             (*pdrv.get()).id_table = T::ID_TABLE.as_ptr();
+            #[cfg(CONFIG_PCI_IOV)]
+            if T::HAS_SRIOV_CONFIGURE {
+                (*pdrv.get()).sriov_configure = Some(Self::sriov_configure_callback);
+            }
         }
 
         // SAFETY: `pdrv` is guaranteed to be a valid `DriverType`.
@@ -135,7 +139,13 @@ extern "C" fn remove_callback(pdev: *mut bindings::pci_dev) {
 
         // Keep PF data installed until all VF remove callbacks have completed.
         #[cfg(CONFIG_PCI_IOV)]
-        pdev.disable_sriov();
+        if pdev.num_vf() != 0 {
+            if T::HAS_SRIOV_CONFIGURE {
+                Self::sriov_configure_callback(pdev.as_raw(), 0);
+                crate::warn_on!(pdev.num_vf() != 0);
+            }
+            pdev.disable_sriov();
+        }
 
         // SAFETY: `remove_callback` is only ever called after a successful call to
         // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
@@ -144,6 +154,20 @@ extern "C" fn remove_callback(pdev: *mut bindings::pci_dev) {
 
         T::unbind(pdev, data);
     }
+
+    #[cfg(CONFIG_PCI_IOV)]
+    extern "C" fn sriov_configure_callback(
+        pdev: *mut bindings::pci_dev,
+        nr_virtfn: c_int,
+    ) -> c_int {
+        // SAFETY: The PCI bus only ever calls the sriov_configure callback with a valid pointer to
+        // a `struct pci_dev`.
+        //
+        // INVARIANT: `pdev` is valid for the duration of `sriov_configure_callback()`.
+        let pdev = unsafe { &*pdev.cast::<Device<device::CoreInternal<'_>>>() };
+
+        from_result(|| T::sriov_configure(pdev, nr_virtfn))
+    }
 }
 
 /// Declares a kernel module that exposes a single PCI driver.
@@ -330,6 +354,44 @@ fn probe<'bound>(
     fn unbind<'bound>(dev: &'bound Device<device::Core<'_>>, this: Pin<&Self::Data<'bound>>) {
         let _ = (dev, this);
     }
+
+    /// Single Root I/O Virtualization (SR-IOV) configure.
+    ///
+    /// Called when a user-space application enables or disables the SR-IOV capability for a
+    /// [`Device`] by writing the number of Virtual Functions (VF), `nr_virtfn` or zero to the
+    /// sysfs file `sriov_numvfs` for this device. Implementing this callback is optional.
+    ///
+    /// Further, and unlike for a PCI driver written in C, when a PF device with enabled VFs is
+    /// unbound from its bound [`Driver`], the `sriov_configure()` callback is invoked to disable
+    /// SR-IOV before the `unbind()` callback. This guarantees that when a VF device is bound to a
+    /// driver, the underlying PF device is bound to a driver, too.
+    ///
+    /// Upon success, this callback must return the number of VFs that were enabled, or zero if
+    /// SR-IOV was disabled.
+    ///
+    /// See [PCI Express I/O Virtualization].
+    ///
+    /// [PCI Express I/O Virtualization]: https://docs.kernel.org/PCI/pci-iov-howto.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use kernel::{device::Core, pci, prelude::*};
+    /// #[cfg(CONFIG_PCI_IOV)]
+    /// fn sriov_configure(dev: &pci::Device<Core<'_>>, nr_virtfn: i32) -> Result<i32> {
+    ///     if nr_virtfn == 0 {
+    ///         dev.disable_sriov();
+    ///     } else {
+    ///         dev.enable_sriov(nr_virtfn)?;
+    ///     }
+    ///     Ok(nr_virtfn)
+    /// }
+    /// ```
+    #[cfg(CONFIG_PCI_IOV)]
+    fn sriov_configure(dev: &Device<device::Core<'_>>, nr_virtfn: i32) -> Result<i32> {
+        let _ = (dev, nr_virtfn);
+        build_error!(crate::error::VTABLE_DEFAULT_ERROR)
+    }
 }
 
 /// The PCI device representation.
@@ -451,7 +513,6 @@ pub(crate) fn is_virtfn(&self) -> bool {
 
     /// Returns the number of Virtual Functions (VF) enabled for a Physical Function (PF).
     #[cfg(CONFIG_PCI_IOV)]
-    #[expect(dead_code)]
     pub(crate) fn num_vf(&self) -> i32 {
         // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`.
         unsafe { bindings::pci_num_vf(self.as_raw()) }
-- 
2.53.0