Re: [PATCH v4 17/27] rust: pci: make Bar lifetime-parameterized

[Eliot Courtney]

On Fri May 22, 2026 at 8:34 AM JST, Danilo Krummrich wrote:
> Convert pci::Bar<SIZE> to pci::Bar<'a, SIZE>, storing &'a Device<Bound>
> to tie the BAR mapping lifetime to the device.
>
> iomap_region_sized() now returns Result<Bar<'a, SIZE>> directly instead
> of impl PinInit<Devres<Bar<SIZE>>, Error>.
>
> Add Bar::into_devres() to consume the bar and register it as a
> device-managed resource, returning Devres<Bar<'static, SIZE>>. The
> lifetime is erased to 'static because Devres guarantees the bar does not
> actually outlive the device -- access is revoked on unbind.
>
> Reviewed-by: Eliot Courtney <ecourtney@xxxxxxxxxx>
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> ---
>  drivers/gpu/nova-core/driver.rs |  7 +++--
>  rust/kernel/devres.rs           |  2 +-
>  rust/kernel/pci/io.rs           | 50 ++++++++++++++++++---------------
>  samples/rust/rust_driver_pci.rs |  5 ++--
>  4 files changed, 35 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
> index 6ad1a856694c..7dbec0470c26 100644
> --- a/drivers/gpu/nova-core/driver.rs
> +++ b/drivers/gpu/nova-core/driver.rs
> @@ -45,7 +45,7 @@ pub(crate) struct NovaCore {
>  // DMA addresses. These systems should be quite rare.
>  const GPU_DMA_BITS: u32 = 47;
>  
> -pub(crate) type Bar0 = pci::Bar<BAR0_SIZE>;
> +pub(crate) type Bar0 = pci::Bar<'static, BAR0_SIZE>;
>  
>  kernel::pci_device_table!(
>      PCI_TABLE,
> @@ -92,8 +92,9 @@ fn probe<'bound>(
>              // other threads of execution.
>              unsafe { pdev.dma_set_mask_and_coherent(DmaMask::new::<GPU_DMA_BITS>())? };
>  
> -            let bar = Arc::pin_init(
> -                pdev.iomap_region_sized::<BAR0_SIZE>(0, c"nova-core/bar0"),
> +            let bar = Arc::new(
> +                pdev.iomap_region_sized::<BAR0_SIZE>(0, c"nova-core/bar0")?
> +                    .into_devres()?,
>                  GFP_KERNEL,
>              )?;
>  
> diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
> index fd4633f977f6..82cbd8b969fb 100644
> --- a/rust/kernel/devres.rs
> +++ b/rust/kernel/devres.rs
> @@ -304,7 +304,7 @@ pub fn device(&self) -> &Device {
>      ///     pci, //
>      /// };
>      ///
> -    /// fn from_core(dev: &pci::Device<Core<'_>>, devres: Devres<pci::Bar<0x4>>) -> Result {
> +    /// fn from_core(dev: &pci::Device<Core<'_>>, devres: Devres<pci::Bar<'_, 0x4>>) -> Result {
>      ///     let bar = devres.access(dev.as_ref())?;
>      ///
>      ///     let _ = bar.read32(0x0);
> diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
> index ae78676c927f..6116c55412bc 100644
> --- a/rust/kernel/pci/io.rs
> +++ b/rust/kernel/pci/io.rs
> @@ -14,8 +14,7 @@
>          Mmio,
>          MmioRaw, //
>      },
> -    prelude::*,
> -    sync::aref::ARef, //
> +    prelude::*, //
>  };
>  use core::{
>      marker::PhantomData,
> @@ -146,14 +145,14 @@ impl<'a, S: ConfigSpaceKind> IoKnownSize for ConfigSpace<'a, S> {
>  ///
>  /// `Bar` always holds an `IoRaw` instance that holds a valid pointer to the start of the I/O
>  /// memory mapped PCI BAR and its size.
> -pub struct Bar<const SIZE: usize = 0> {
> -    pdev: ARef<Device>,
> +pub struct Bar<'a, const SIZE: usize = 0> {
> +    pdev: &'a Device<device::Bound>,
>      io: MmioRaw<SIZE>,
>      num: i32,
>  }
>  
> -impl<const SIZE: usize> Bar<SIZE> {
> -    pub(super) fn new(pdev: &Device, num: u32, name: &CStr) -> Result<Self> {
> +impl<'a, const SIZE: usize> Bar<'a, SIZE> {
> +    pub(super) fn new(pdev: &'a Device<device::Bound>, num: u32, name: &CStr) -> Result<Self> {

I think Sashiko's comment w.r.t. &CStrs in this patch looks accurate
and they should be 'static or at least 'a ish.

still
Reviewed-by: Eliot Courtney <ecourtney@xxxxxxxxxx>