Re: [PATCH v10 5/6] gpu: nova-core: create debugfs root in module init

["Alexandre Courbot" <acourbot@nvidia.com>]

On Wed Mar 18, 2026 at 8:54 AM JST, Timur Tabi wrote:
> Create the 'nova_core' root debugfs entry when the driver loads.
>
> Normally, non-const global variables need to be protected by a
> mutex.  Instead, we use unsafe code, as we know the entry is never
> modified after the driver is loaded.  This solves the lifetime
> issue of the mutex guard, which would otherwise have required the
> use of `pin_init_scope`.
>
> Signed-off-by: Timur Tabi <ttabi@nvidia.com>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Tested-by: John Hubbard <jhubbard@nvidia.com>
> Tested-by: Eliot Courtney <ecourtney@nvidia.com>
> ---

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

With a few nitty nits below.

>  drivers/gpu/nova-core/nova_core.rs | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/drivers/gpu/nova-core/nova_core.rs b/drivers/gpu/nova-core/nova_core.rs
> index 0114a59825aa..b7e6c6274aa8 100644
> --- a/drivers/gpu/nova-core/nova_core.rs
> +++ b/drivers/gpu/nova-core/nova_core.rs
> @@ -3,6 +3,7 @@
>  //! Nova Core GPU Driver
>  
>  use kernel::{
> +    debugfs,
>      driver::Registration,
>      pci,
>      prelude::*,
> @@ -27,16 +28,40 @@
>  
>  pub(crate) const MODULE_NAME: &core::ffi::CStr = <LocalModule as kernel::ModuleMetadata>::NAME;
>  
> +// FIXME: Move this into per-module data once that exists

I'd change this to do `TODO:` for easier discovery.

> +static mut DEBUGFS_ROOT: Option<debugfs::Dir> = None;
> +
> +/// Guard that clears DEBUGFS_ROOT when dropped.

Item names need `` quotes.

> +struct DebugfsRootGuard;
> +
> +impl Drop for DebugfsRootGuard {
> +    fn drop(&mut self) {
> +        // SAFETY: This guard is dropped after _driver (due to field order),
> +        // so the driver is unregistered and no probe() can be running.

Here as well (even if it's not a doccomment).

> +        unsafe { DEBUGFS_ROOT = None };
> +    }
> +}
> +
>  #[pin_data]
>  struct NovaCoreModule {
> +    // Fields are dropped in declaration order, so _driver is dropped first,
> +    // then _debugfs_guard clears DEBUGFS_ROOT.

And here.