linux-kernel - Re: [PATCH v2 07/19] gpu: nova-core: register: move OFFSET declaration to I/O impl block

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Message-Id: <856B6814-1782-4FB0-9DD1-BD46C8FE935C@collabora.com>
Date: Fri, 25 Jul 2025 14:03:09 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alexandre Courbot <acourbot@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>,
 David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>,
 Beata Michalska <beata.michalska@....com>,
 nouveau@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org,
 rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 07/19] gpu: nova-core: register: move OFFSET
 declaration to I/O impl block



> On 18 Jul 2025, at 04:26, Alexandre Courbot <acourbot@...dia.com> wrote:
> 
> The OFFSET const is an I/O property, and having to pass it to the
> @common rule makes it impossible to make I/O optional, as we want to get
> to eventually.
> 
> Thus, move OFFSET to the I/O impl block so it is not needed by the
> @common rule anymore.
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
> drivers/gpu/nova-core/regs/macros.rs | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/nova-core/regs/macros.rs b/drivers/gpu/nova-core/regs/macros.rs
> index 742afd3ae1a3c798817bbf815945889077ce10d0..4da897787c065e69657ce65327e3290af403a615 100644
> --- a/drivers/gpu/nova-core/regs/macros.rs
> +++ b/drivers/gpu/nova-core/regs/macros.rs
> @@ -92,7 +92,7 @@ macro_rules! register {
>             $($fields:tt)*
>         }
>     ) => {
> -        register!(@common $name @ $offset $(, $comment)?);
> +        register!(@common $name $(, $comment)?);
>         register!(@field_accessors $name { $($fields)* });
>         register!(@io $name @ $offset);
>     };
> @@ -103,7 +103,7 @@ macro_rules! register {
>             $($fields:tt)*
>         }
>     ) => {
> -        register!(@common $name @ $alias::OFFSET $(, $comment)?);
> +        register!(@common $name $(, $comment)?);
>         register!(@field_accessors $name { $($fields)* });
>         register!(@io $name @ $alias::OFFSET);
>     };
> @@ -114,7 +114,7 @@ macro_rules! register {
>             $($fields:tt)*
>         }
>     ) => {
> -        register!(@common $name @ $offset $(, $comment)?);
> +        register!(@common $name $(, $comment)?);
>         register!(@field_accessors $name { $($fields)* });
>         register!(@io $name @ + $offset);
>     };
> @@ -125,7 +125,7 @@ macro_rules! register {
>             $($fields:tt)*
>         }
>     ) => {
> -        register!(@common $name @ $alias::OFFSET $(, $comment)?);
> +        register!(@common $name $(, $comment)?);
>         register!(@field_accessors $name { $($fields)* });
>         register!(@io $name @ + $alias::OFFSET);
>     };
> @@ -134,7 +134,7 @@ macro_rules! register {
> 
>     // Defines the wrapper `$name` type, as well as its relevant implementations (`Debug`, `BitOr`,
>     // and conversion to regular `u32`).
> -    (@common $name:ident @ $offset:expr $(, $comment:literal)?) => {
> +    (@common $name:ident $(, $comment:literal)?) => {
>         $(
>         #[doc=$comment]
>         )?
> @@ -142,11 +142,6 @@ macro_rules! register {
>         #[derive(Clone, Copy, Default)]
>         pub(crate) struct $name(u32);
> 
> -        #[allow(dead_code)]
> -        impl $name {
> -            pub(crate) const OFFSET: usize = $offset;
> -        }
> -
>         // TODO[REGA]: display the raw hex value, then the value of all the fields. This requires
>         // matching the fields, which will complexify the syntax considerably...
>         impl ::core::fmt::Debug for $name {
> @@ -319,6 +314,8 @@ pub(crate) fn [<set_ $field>](mut self, value: $to_type) -> Self {
>     (@io $name:ident @ $offset:expr) => {
>         #[allow(dead_code)]
>         impl $name {
> +            pub(crate) const OFFSET: usize = $offset;
> +

Minor suggestion, have you ever though about somehow making this a const
generic? This saves the space needed to store the actual constant in the
binary.

Again, not sure whether this is feasible.


>             #[inline]
>             pub(crate) fn read<const SIZE: usize, T>(io: &T) -> Self where
>                 T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
> @@ -351,6 +348,8 @@ pub(crate) fn alter<const SIZE: usize, T, F>(
>     (@io $name:ident @ + $offset:literal) => {
>         #[allow(dead_code)]
>         impl $name {
> +            pub(crate) const OFFSET: usize = $offset;
> +
>             #[inline]
>             pub(crate) fn read<const SIZE: usize, T>(
>                 io: &T,
> 
> -- 
> 2.50.1
> 

Reviewed-by: Daniel Almeida <daniel.almeida@...labora.com>