[PATCH] rust: pci: add resource_flags accessor

[PATCH] rust: pci: add resource_flags accessor

[Eliot Courtney]

From: 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>
Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
---
This is patch 1 of Joel's nova-core mm prerequisites series [1],
reposted with no code changes. The rest of that series was folded into
the PRAMIN series [2], which is now in drm-rust-next and didn't carry
this patch. The upcoming nova-core memory management changes still need
resource_flags().

This is based on drm-rust-next.

[1] https://lore.kernel.org/all/20260518180342.2387845-2-joelagnelf@nvidia.com/
[2] https://lore.kernel.org/all/20260827-pramin-split-v3-0-24b24d7afc52@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 a714cc2bfb7a..3686e405160d 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 17b0c174cfc5..0d3b34f83334 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 {
         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 3ec897709e89..19a219847c17 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,
@@ -439,6 +440,19 @@ 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 {

---
base-commit: e6a2c988ed96a5a3af51ed97ecba980521bf2fc0
change-id: 20260907-pci-resource-flags-b7addba0b34f

Best regards,
--  
Eliot Courtney <ecourtney@nvidia.com>

Re: [PATCH] rust: pci: add resource_flags accessor

[Danilo Krummrich]

On 9/8/26 9:51 AM, Eliot Courtney wrote:
> From: 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>
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
> ---
> This is patch 1 of Joel's nova-core mm prerequisites series [1],
> reposted with no code changes. The rest of that series was folded into
> the PRAMIN series [2], which is now in drm-rust-next and didn't carry
> this patch. The upcoming nova-core memory management changes still need
> resource_flags().
> 
> This is based on drm-rust-next.

Acked-by: Danilo Krummrich <dakr@kernel.org>

Re: [PATCH] rust: pci: add resource_flags accessor

[Alexandre Courbot]

On Tue Sep 8, 2026 at 4:51 PM JST, Eliot Courtney wrote:
> From: 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>
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

Re: [PATCH] rust: pci: add resource_flags accessor

[Eliot Courtney]

On Tue Sep 8, 2026 at 4:51 PM JST, Eliot Courtney wrote:
> From: 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>
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
> ---
> This is patch 1 of Joel's nova-core mm prerequisites series [1],
> reposted with no code changes. The rest of that series was folded into
> the PRAMIN series [2], which is now in drm-rust-next and didn't carry
> this patch. The upcoming nova-core memory management changes still need
> resource_flags().
>
> This is based on drm-rust-next.
>
> [1] https://lore.kernel.org/all/20260518180342.2387845-2-joelagnelf@nvidia.com/
> [2] https://lore.kernel.org/all/20260827-pramin-split-v3-0-24b24d7afc52@nvidia.com/
> ---

Applied to drm-rust-next, thanks!

[1/1] rust: pci: add resource_flags accessor
      commit: 3f1e12fce16f6e88fbaab3404df33f65c8f4df87

Re: [PATCH] rust: pci: add resource_flags accessor

[Miguel Ojeda]

On Tue, 08 Sep 2026 16:51:48 +0900 Eliot Courtney <ecourtney@nvidia.com> wrote:
>
> +    /// 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)
> +    }

In linux-next (next-20261022), on UML x86_64, I am seeing:

    error: associated function `from_raw` is never used
       --> rust/kernel/io/resource.rs:240:25
        |
    216 | impl Flags {
        | ---------- associated function in this implementation
    ...
    240 |     pub(crate) const fn from_raw(value: c_ulong) -> Self {
        |                         ^^^^^^^^
        |
        = note: `-D dead-code` implied by `-D warnings`
        = help: to override `-D warnings` add `#[allow(dead_code)]`

`kernel::io::resource` is always built, but the only user of `from_raw`
is under `CONFIG_PCI`.

I hope that helps.

Cheers,
Miguel