[PATCH v1 01/12] rust: pci: add resource_flags accessor

[Joel Fernandes <joelagnelf@nvidia.com>]

Add a `Device::resource_flags()` method to the PCI Rust abstraction,
wrapping the C-side static inline `pci_resource_flags()`.

The flags returned correspond to the `IORESOURCE` bitmask carried by a
PCI BAR's `struct resource`.

The immediate motivation is BAR layout discovery on NVIDIA GPUs: a
64-bit BAR consumes two consecutive Linux PCI resource slots (the lower
32 bits at index N and the upper 32 bits at index N+1, with the latter
having no flags or size of its own).

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
 rust/helpers/pci.c         |  6 ++++++
 rust/kernel/io/resource.rs |  8 ++++++++
 rust/kernel/pci.rs         | 14 ++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/rust/helpers/pci.c b/rust/helpers/pci.c
index e44905317d75..51148987618a 100644
--- a/rust/helpers/pci.c
+++ b/rust/helpers/pci.c
@@ -19,6 +19,12 @@ __rust_helper resource_size_t rust_helper_pci_resource_len(struct pci_dev *pdev,
 	return pci_resource_len(pdev, bar);
 }
 
+__rust_helper unsigned long rust_helper_pci_resource_flags(const struct pci_dev *pdev,
+							   int bar)
+{
+	return pci_resource_flags(pdev, bar);
+}
+
 __rust_helper bool rust_helper_dev_is_pci(const struct device *dev)
 {
 	return dev_is_pci(dev);
diff --git a/rust/kernel/io/resource.rs b/rust/kernel/io/resource.rs
index b7ac9faf141d..78f353d1605b 100644
--- a/rust/kernel/io/resource.rs
+++ b/rust/kernel/io/resource.rs
@@ -226,10 +226,18 @@ impl Flags {
     /// Resource represents a memory region that must be ioremaped using `ioremap_np`.
     pub const IORESOURCE_MEM_NONPOSTED: Flags = Flags::new(bindings::IORESOURCE_MEM_NONPOSTED);
 
+    /// Memory region uses a 64-bit address (consumes two consecutive PCI resource slots).
+    pub const IORESOURCE_MEM_64: Flags = Flags::new(bindings::IORESOURCE_MEM_64);
+
     // Always inline to optimize out error path of `build_assert`.
     #[inline(always)]
     const fn new(value: u32) -> Self {
         crate::build_assert!(value as u64 <= c_ulong::MAX as u64);
         Flags(value as c_ulong)
     }
+
+    /// Wrap a raw `c_ulong` value returned by a C API into [`Flags`].
+    pub(crate) const fn from_raw(value: c_ulong) -> Self {
+        Flags(value)
+    }
 }
diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index af74ddff6114..d76a1377195e 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -17,6 +17,7 @@
         from_result,
         to_result, //
     },
+    io::resource,
     prelude::*,
     str::CStr,
     types::Opaque,
@@ -437,6 +438,19 @@ pub fn resource_len(&self, bar: u32) -> Result<bindings::resource_size_t> {
         Ok(unsafe { bindings::pci_resource_len(self.as_raw(), bar.try_into()?) })
     }
 
+    /// Returns the resource flags (`IORESOURCE_*`) of the given PCI BAR.
+    pub fn resource_flags(&self, bar: u32) -> Result<resource::Flags> {
+        if !Bar::index_is_valid(bar) {
+            return Err(EINVAL);
+        }
+
+        // SAFETY:
+        // - `bar` is a valid bar number, as guaranteed by the above call to `Bar::index_is_valid`,
+        // - by its type invariant `self.as_raw` is always a valid pointer to a `struct pci_dev`.
+        let raw = unsafe { bindings::pci_resource_flags(self.as_raw(), bar.try_into()?) };
+        Ok(resource::Flags::from_raw(raw))
+    }
+
     /// Returns the PCI class as a `Class` struct.
     #[inline]
     pub fn pci_class(&self) -> Class {
-- 
2.34.1