[PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[Eliot Courtney]

The current implementation does not actually set the default values for
the fields in the bitfield.

Fixes: 3fa145bef533 ("gpu: nova-core: register: generate correct `Default` implementation")
Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
---
It doesn't actually set the default values for each field. I know that
bitfields are being moved soon, so maybe this fix is unnecessary but I
saw it and it's a simple fix.
---
Changes in v2:
- add "Fixes"
- remove test
- Link to v1: https://patch.msgid.link/20260331-fix-bitfield-v1-1-ebe1a72b4fae@nvidia.com
---
 drivers/gpu/nova-core/bitfield.rs | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/nova-core/bitfield.rs b/drivers/gpu/nova-core/bitfield.rs
index 16e143658c51..02efdcf78d89 100644
--- a/drivers/gpu/nova-core/bitfield.rs
+++ b/drivers/gpu/nova-core/bitfield.rs
@@ -314,12 +314,11 @@ fn fmt(&self, f: &mut ::kernel::fmt::Formatter<'_>) -> ::kernel::fmt::Result {
         /// Returns a value for the bitfield where all fields are set to their default value.
         impl ::core::default::Default for $name {
             fn default() -> Self {
-                #[allow(unused_mut)]
-                let mut value = Self(Default::default());
+                let value = Self(Default::default());
 
                 ::kernel::macros::paste!(
                 $(
-                value.[<set_ $field>](Default::default());
+                let value = value.[<set_ $field>](Default::default());
                 )*
                 );
 

---
base-commit: 7c50d748b4a635bc39802ea3f6b120e66b1b9067
change-id: 20260331-fix-bitfield-a03f6d1b9e00

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

Re: [PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[Alexandre Courbot]

On Wed Apr 1, 2026 at 10:42 AM JST, Eliot Courtney wrote:
> The current implementation does not actually set the default values for
> the fields in the bitfield.
>
> Fixes: 3fa145bef533 ("gpu: nova-core: register: generate correct `Default` implementation")
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>

Don't forget to collect the tags you received on v1 (I use b4 which will
do it anyway so no biggie, but not everybody does).

> ---
> It doesn't actually set the default values for each field. I know that
> bitfields are being moved soon, so maybe this fix is unnecessary but I
> saw it and it's a simple fix.

Fixing it is the correct course imho - the common bitfield macro still
needs to undergo extensive review, and we might hit some hard-to-debug
issue in Nova because of this bug. I'll apply it as soon as
drm-rust-next reopens, thanks!

Re: [PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[Gary Guo]

On Wed Apr 1, 2026 at 5:26 AM BST, Alexandre Courbot wrote:
> On Wed Apr 1, 2026 at 10:42 AM JST, Eliot Courtney wrote:
>> The current implementation does not actually set the default values for
>> the fields in the bitfield.
>>
>> Fixes: 3fa145bef533 ("gpu: nova-core: register: generate correct `Default` implementation")
>> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
>
> Don't forget to collect the tags you received on v1 (I use b4 which will
> do it anyway so no biggie, but not everybody does).
>
>> ---
>> It doesn't actually set the default values for each field. I know that
>> bitfields are being moved soon, so maybe this fix is unnecessary but I
>> saw it and it's a simple fix.
>
> Fixing it is the correct course imho - the common bitfield macro still
> needs to undergo extensive review, and we might hit some hard-to-debug
> issue in Nova because of this bug. I'll apply it as soon as
> drm-rust-next reopens, thanks!

This could go via drm-rust-fixes?

Best,
Gary

Re: [PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[Danilo Krummrich]

On 4/1/26 5:35 PM, Gary Guo wrote:
> This could go via drm-rust-fixes?

It seems there's nothing actually broken due to that, so no need to take it
through -fixes. But we can pick it up before drm-rust-next opens for new
features as I will send another -next PR for the unsoundness fix anyways.

Re: [PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[Eliot Courtney]

On Thu Apr 2, 2026 at 12:44 AM JST, Danilo Krummrich wrote:
> On 4/1/26 5:35 PM, Gary Guo wrote:
>> This could go via drm-rust-fixes?
>
> It seems there's nothing actually broken due to that, so no need to take it
> through -fixes. But we can pick it up before drm-rust-next opens for new
> features as I will send another -next PR for the unsoundness fix anyways.

Yes, nothing actually broken from this right now.

Thanks all

Re: [PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[Danilo Krummrich]

On Wed Apr 1, 2026 at 3:42 AM CEST, Eliot Courtney wrote:
> The current implementation does not actually set the default values for
> the fields in the bitfield.
>
> Fixes: 3fa145bef533 ("gpu: nova-core: register: generate correct `Default` implementation")
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>

Applied to drm-rust-next, thanks!

Re: [PATCH v2] gpu: nova-core: bitfield: fix broken Default implementation

[Danilo Krummrich]

On Wed Apr 1, 2026 at 3:42 AM CEST, Eliot Courtney wrote:
> The current implementation does not actually set the default values for
> the fields in the bitfield.
>
> Fixes: 3fa145bef533 ("gpu: nova-core: register: generate correct `Default` implementation")
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>

Due to [1] I dropped this one as well for now; I will pick it up once -rc1 is
out.

Thanks,
Danilo

[1] https://lore.kernel.org/all/DHJXK4PAD7V0.3UYK35FDHRNIK@kernel.org/