* [PATCH v3 1/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs
2025-12-09 2:57 [PATCH v3 0/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs Alexandre Courbot
@ 2025-12-09 2:57 ` Alexandre Courbot
2025-12-09 12:14 ` Benno Lossin
2025-12-09 2:58 ` [PATCH v3 2/2] gpu: nova-core: gsp: use () as message type for GspInitDone message Alexandre Courbot
2025-12-09 12:18 ` [PATCH v3 0/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs Gary Guo
2 siblings, 1 reply; 6+ messages in thread
From: Alexandre Courbot @ 2025-12-09 2:57 UTC (permalink / raw)
To: Miguel Ojeda, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Danilo Krummrich
Cc: John Hubbard, Alistair Popple, Joel Fernandes, Timur Tabi,
Edwin Peer, Eliot Courtney, rust-for-linux, linux-kernel,
Alexandre Courbot
This is useful when using types that may or may not be empty in generic
code relying on these traits. It is also safe because technically a
no-op.
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
rust/kernel/transmute.rs | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
index be5dbf3829e2..a888a312e7ff 100644
--- a/rust/kernel/transmute.rs
+++ b/rust/kernel/transmute.rs
@@ -170,6 +170,10 @@ macro_rules! impl_frombytes {
}
impl_frombytes! {
+ // SAFETY: Inhabited ZSTs only have one possible bit pattern.
+ (),
+ {<T>} core::marker::PhantomData<T>,
+
// SAFETY: All bit patterns are acceptable values of the types below.
u8, u16, u32, u64, usize,
i8, i16, i32, i64, isize,
@@ -230,6 +234,10 @@ macro_rules! impl_asbytes {
}
impl_asbytes! {
+ // SAFETY: Inhabited ZSTs only have one possible bit pattern.
+ (),
+ {<T>} core::marker::PhantomData<T>,
+
// SAFETY: Instances of the following types have no uninitialized portions.
u8, u16, u32, u64, usize,
i8, i16, i32, i64, isize,
--
2.52.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v3 1/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs
2025-12-09 2:57 ` [PATCH v3 1/2] " Alexandre Courbot
@ 2025-12-09 12:14 ` Benno Lossin
2025-12-11 1:21 ` Alice Ryhl
0 siblings, 1 reply; 6+ messages in thread
From: Benno Lossin @ 2025-12-09 12:14 UTC (permalink / raw)
To: Alexandre Courbot, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Danilo Krummrich
Cc: John Hubbard, Alistair Popple, Joel Fernandes, Timur Tabi,
Edwin Peer, Eliot Courtney, rust-for-linux, linux-kernel
On Tue Dec 9, 2025 at 3:57 AM CET, Alexandre Courbot wrote:
> This is useful when using types that may or may not be empty in generic
> code relying on these traits. It is also safe because technically a
> no-op.
>
> Reviewed-by: Alistair Popple <apopple@nvidia.com>
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
> rust/kernel/transmute.rs | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
> index be5dbf3829e2..a888a312e7ff 100644
> --- a/rust/kernel/transmute.rs
> +++ b/rust/kernel/transmute.rs
> @@ -170,6 +170,10 @@ macro_rules! impl_frombytes {
> }
>
> impl_frombytes! {
> + // SAFETY: Inhabited ZSTs only have one possible bit pattern.
Even inhabited ZSTs cannot just be conjured out of thin air, since there
might be safety invariants on the creation of such a type. Now these
two concrete ones do not have any, so this is fine, but should still be
mentioned in the comment IMO.
Cheers,
Benno
> + (),
> + {<T>} core::marker::PhantomData<T>,
> +
> // SAFETY: All bit patterns are acceptable values of the types below.
> u8, u16, u32, u64, usize,
> i8, i16, i32, i64, isize,
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v3 1/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs
2025-12-09 12:14 ` Benno Lossin
@ 2025-12-11 1:21 ` Alice Ryhl
0 siblings, 0 replies; 6+ messages in thread
From: Alice Ryhl @ 2025-12-11 1:21 UTC (permalink / raw)
To: Benno Lossin
Cc: Alexandre Courbot, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Andreas Hindborg, Trevor Gross,
Danilo Krummrich, John Hubbard, Alistair Popple, Joel Fernandes,
Timur Tabi, Edwin Peer, Eliot Courtney, rust-for-linux,
linux-kernel
On Tue, Dec 09, 2025 at 01:14:08PM +0100, Benno Lossin wrote:
> On Tue Dec 9, 2025 at 3:57 AM CET, Alexandre Courbot wrote:
> > This is useful when using types that may or may not be empty in generic
> > code relying on these traits. It is also safe because technically a
> > no-op.
> >
> > Reviewed-by: Alistair Popple <apopple@nvidia.com>
> > Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> > ---
> > rust/kernel/transmute.rs | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/rust/kernel/transmute.rs b/rust/kernel/transmute.rs
> > index be5dbf3829e2..a888a312e7ff 100644
> > --- a/rust/kernel/transmute.rs
> > +++ b/rust/kernel/transmute.rs
> > @@ -170,6 +170,10 @@ macro_rules! impl_frombytes {
> > }
> >
> > impl_frombytes! {
> > + // SAFETY: Inhabited ZSTs only have one possible bit pattern.
>
> Even inhabited ZSTs cannot just be conjured out of thin air, since there
> might be safety invariants on the creation of such a type. Now these
> two concrete ones do not have any, so this is fine, but should still be
> mentioned in the comment IMO.
I think we can say "it has no invariants".
Alice
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v3 2/2] gpu: nova-core: gsp: use () as message type for GspInitDone message
2025-12-09 2:57 [PATCH v3 0/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs Alexandre Courbot
2025-12-09 2:57 ` [PATCH v3 1/2] " Alexandre Courbot
@ 2025-12-09 2:58 ` Alexandre Courbot
2025-12-09 12:18 ` [PATCH v3 0/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs Gary Guo
2 siblings, 0 replies; 6+ messages in thread
From: Alexandre Courbot @ 2025-12-09 2:58 UTC (permalink / raw)
To: Miguel Ojeda, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Danilo Krummrich
Cc: John Hubbard, Alistair Popple, Joel Fernandes, Timur Tabi,
Edwin Peer, Eliot Courtney, rust-for-linux, linux-kernel,
Alexandre Courbot
`GspInitDone` has no payload whatsoever, so the unit type `()` is the
correct way to represent its message content. We can use it now that
`()` implements `FromBytes`.
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
---
drivers/gpu/nova-core/gsp/commands.rs | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index 0425c65b5d6f..2050771f9b53 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -142,7 +142,7 @@ fn init_variable_payload(
}
/// Message type for GSP initialization done notification.
-struct GspInitDone {}
+struct GspInitDone;
// SAFETY: `GspInitDone` is a zero-sized type with no bytes, therefore it
// trivially has no uninitialized bytes.
@@ -151,13 +151,13 @@ unsafe impl FromBytes for GspInitDone {}
impl MessageFromGsp for GspInitDone {
const FUNCTION: MsgFunction = MsgFunction::GspInitDone;
type InitError = Infallible;
- type Message = GspInitDone;
+ type Message = ();
fn read(
_msg: &Self::Message,
_sbuffer: &mut SBufferIter<array::IntoIter<&[u8], 2>>,
) -> Result<Self, Self::InitError> {
- Ok(GspInitDone {})
+ Ok(GspInitDone)
}
}
--
2.52.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH v3 0/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs
2025-12-09 2:57 [PATCH v3 0/2] rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs Alexandre Courbot
2025-12-09 2:57 ` [PATCH v3 1/2] " Alexandre Courbot
2025-12-09 2:58 ` [PATCH v3 2/2] gpu: nova-core: gsp: use () as message type for GspInitDone message Alexandre Courbot
@ 2025-12-09 12:18 ` Gary Guo
2 siblings, 0 replies; 6+ messages in thread
From: Gary Guo @ 2025-12-09 12:18 UTC (permalink / raw)
To: Alexandre Courbot
Cc: Miguel Ojeda, Boqun Feng, Björn Roy Baron, Benno Lossin,
Andreas Hindborg, Alice Ryhl, Trevor Gross, Danilo Krummrich,
John Hubbard, Alistair Popple, Joel Fernandes, Timur Tabi,
Edwin Peer, Eliot Courtney, rust-for-linux, linux-kernel
On Tue, 09 Dec 2025 11:57:58 +0900
Alexandre Courbot <acourbot@nvidia.com> wrote:
> This is useful in Nova's GSP message handling, as some messages are
> empty and we currently need to explicitly use an empty structure for
> them.
>
> If accepted, I would like to merge it through `drm-rust-next` so Nova
> code can start using this feature quickly.
>
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
> ---
> Changes in v3:
> - Use better safety statement. (thanks Gary!)
> - Also add `PhantomData`. (thanks Gary!)
> - Link to v2: https://patch.msgid.link/20251208-transmute_unit-v2-0-aa17a6848afb@nvidia.com
>
> Changes in v2:
> - Make use of new feature in Nova.
> - Link to v1: https://patch.msgid.link/20251208-transmute_unit-v1-1-680c7386b5d9@nvidia.com
>
> ---
> Alexandre Courbot (2):
> rust: transmute: implement FromBytes and AsBytes for inhabited ZSTs
> gpu: nova-core: gsp: use () as message type for GspInitDone message
>
> drivers/gpu/nova-core/gsp/commands.rs | 6 +++---
> rust/kernel/transmute.rs | 8 ++++++++
> 2 files changed, 11 insertions(+), 3 deletions(-)
> ---
> base-commit: ba65a4e7120a616d9c592750d9147f6dcafedffa
> change-id: 20251208-transmute_unit-78ab58ba9e6e
>
> Best regards,
^ permalink raw reply [flat|nested] 6+ messages in thread