From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2510CCA0EFA for ; Tue, 26 Aug 2025 07:42:50 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2A6D410E5CB; Tue, 26 Aug 2025 07:42:43 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=weathered-steel.dev header.i=@weathered-steel.dev header.b="Kw7HvHkO"; dkim-atps=neutral Received: from mail-4327.protonmail.ch (mail-4327.protonmail.ch [185.70.43.27]) by gabe.freedesktop.org (Postfix) with ESMTPS id E56AB10E5A4 for ; Mon, 25 Aug 2025 23:20:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=weathered-steel.dev; s=protonmail3; t=1756164027; x=1756423227; bh=dbfxHDr+4prCVmBev/sJiog2Lc66l2bjBKk57p6NvnI=; h=Date:From:To:Cc:Subject:Message-ID:References:In-Reply-To:From:To: Cc:Date:Subject:Reply-To:Feedback-ID:Message-ID:BIMI-Selector; b=Kw7HvHkOW/t/7aBcbbaxEWgJIAosTbK9FiF/6CDyQESX2BXBlTRAFBUsx8tZMfYAr db6I272BNYVLGhyhLUyUt86/sxo7RmXvwpjm8C+Jjkr6JyInW0/IQOAJVfpeF90Zzj 5+nWo4hHFKRADJMvcZTjlkhAKamuNUw58vSUs7fVOJwNUZ+ypNoX6ybtgrOTqt75Yx yea2VWK69D3FhqUjpwyABmkcfz2XUDQq1VoKse3WnJus3t53cG1bvF/aEuAhTVNkiR BfCPH2IfwZzREM40vUa2Qc7C0DylCv6VtERKOBfbExqguu0BHpwvtB36zuKpOjPWJ6 8cI9ZlrrjiWNA== X-Pm-Submission-Id: 4c9mx60wYnz1DDLJ Date: Mon, 25 Aug 2025 23:20:22 +0000 From: Elle Rhumsaa To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, Danilo Krummrich , Alexandre Courbot , David Airlie , Simona Vetter , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , John Hubbard , Alistair Popple , nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org Subject: Re: [PATCH 1/2] nova-core: Add a library for bitfields in Rust structs Message-ID: References: <20250824135954.2243774-1-joelagnelf@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250824135954.2243774-1-joelagnelf@nvidia.com> X-Mailman-Approved-At: Tue, 26 Aug 2025 07:42:42 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Sun, Aug 24, 2025 at 09:59:52AM -0400, Joel Fernandes wrote: > Add a minimal bitfield library for defining in Rust structures (called > bitstruct), similar in concept to bit fields in C structs. This will be used > for defining page table entries and other structures in nova-core. > > Signed-off-by: Joel Fernandes > --- > drivers/gpu/nova-core/bitstruct.rs | 149 +++++++++++++++++++++++++++++ > drivers/gpu/nova-core/nova_core.rs | 1 + > 2 files changed, 150 insertions(+) > create mode 100644 drivers/gpu/nova-core/bitstruct.rs > > diff --git a/drivers/gpu/nova-core/bitstruct.rs b/drivers/gpu/nova-core/bitstruct.rs > new file mode 100644 > index 000000000000..661a75da0a9c > --- /dev/null > +++ b/drivers/gpu/nova-core/bitstruct.rs > @@ -0,0 +1,149 @@ > +// SPDX-License-Identifier: GPL-2.0 > +// > +// bitstruct.rs — C-style library for bitfield-packed Rust structures > +// > +// A library that provides support for defining bit fields in Rust > +// structures to circumvent lack of native language support for this. > +// > +// Similar usage syntax to the register! macro. > + > +use kernel::prelude::*; > + > +/// Macro for defining bitfield-packed structures in Rust. > +/// The size of the underlying storage type is specified with #[repr(TYPE)]. > +/// > +/// # Example (just for illustration) > +/// ```rust > +/// bitstruct! { > +/// #[repr(u64)] > +/// pub struct PageTableEntry { > +/// 0:0 present as bool, > +/// 1:1 writable as bool, > +/// 11:9 available as u8, > +/// 51:12 pfn as u64, > +/// 62:52 available2 as u16, > +/// 63:63 nx as bool, > +/// } > +/// } > +/// ``` > +/// > +/// This generates a struct with methods: > +/// - Constructor: `default()` sets all bits to zero. > +/// - Field accessors: `present()`, `pfn()`, etc. > +/// - Field setters: `set_present()`, `set_pfn()`, etc. > +/// - Builder methods: `with_present()`, `with_pfn()`, etc. > +/// - Raw conversion: `from_raw()`, `into_raw()` > +#[allow(unused_macros)] > +macro_rules! bitstruct { > + ( > + #[repr($storage:ty)] > + $vis:vis struct $name:ident { > + $( > + $hi:literal : $lo:literal $field:ident as $field_type:tt > + ),* $(,)? > + } > + ) => { > + #[repr(transparent)] > + #[derive(Copy, Clone, Default)] > + $vis struct $name($storage); > + > + impl $name { > + /// Create from raw value > + #[inline(always)] > + $vis const fn from_raw(val: $storage) -> Self { > + Self(val) > + } > + > + /// Get raw value > + #[inline(always)] > + $vis const fn into_raw(self) -> $storage { > + self.0 > + } > + } > + > + impl core::fmt::Debug for $name { > + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { > + write!(f, "{}({:#x})", stringify!($name), self.0) > + } > + } > + > + // Generate all field methods > + $( > + bitstruct_field_impl!($vis, $name, $storage, $hi, $lo, $field as $field_type); > + )* > + }; > +} > + > +/// Helper to calculate mask for bit fields > +#[allow(unused_macros)] > +macro_rules! bitstruct_mask { > + ($hi:literal, $lo:literal, $storage:ty) => {{ > + let width = ($hi - $lo + 1) as usize; > + let storage_bits = 8 * core::mem::size_of::<$storage>(); > + if width >= storage_bits { > + <$storage>::MAX > + } else { > + ((1 as $storage) << width) - 1 > + } > + }}; > +} > + > +#[allow(unused_macros)] > +macro_rules! bitstruct_field_impl { > + ($vis:vis, $struct_name:ident, $storage:ty, $hi:literal, $lo:literal, $field:ident as $field_type:tt) => { > + impl $struct_name { > + #[inline(always)] > + $vis const fn $field(&self) -> $field_type { > + let field_val = (self.0 >> $lo) & bitstruct_mask!($hi, $lo, $storage); > + bitstruct_cast_value!(field_val, $field_type) > + } > + } > + bitstruct_make_setters!($vis, $struct_name, $storage, $hi, $lo, $field, $field_type); > + }; > +} > + > +/// Helper macro to convert extracted value to target type > +/// > +/// Special handling for bool types is required because the `as` keyword > +/// cannot be used to convert to bool in Rust. For bool fields, we check > +/// if the extracted value is non-zero. For all other types, we use the > +/// standard `as` conversion. > +#[allow(unused_macros)] > +macro_rules! bitstruct_cast_value { > + ($field_val:expr, bool) => { > + $field_val != 0 > + }; > + ($field_val:expr, $field_type:tt) => { > + $field_val as $field_type > + }; > +} > + > +#[allow(unused_macros)] > +macro_rules! bitstruct_write_bits { > + ($raw:expr, $hi:literal, $lo:literal, $val:expr, $storage:ty) => {{ > + let mask = bitstruct_mask!($hi, $lo, $storage); > + ($raw & !(mask << $lo)) | ((($val as $storage) & mask) << $lo) > + }}; > +} > + > +#[allow(unused_macros)] > +macro_rules! bitstruct_make_setters { > + ($vis:vis, $struct_name:ident, $storage:ty, $hi:literal, $lo:literal, $field:ident, $field_type:tt) => { > + ::kernel::macros::paste! { > + impl $struct_name { > + #[inline(always)] > + #[allow(dead_code)] > + $vis fn [](&mut self, val: $field_type) { > + self.0 = bitstruct_write_bits!(self.0, $hi, $lo, val, $storage); > + } > + > + #[inline(always)] > + #[allow(dead_code)] > + $vis const fn [](mut self, val: $field_type) -> Self { > + self.0 = bitstruct_write_bits!(self.0, $hi, $lo, val, $storage); > + self > + } > + } > + } > + }; > +} This is awesome. Is there a place for this to live outside of `nova-core`? I would think this would be extremely useful as a general helper for bitfield struct definitions. > diff --git a/drivers/gpu/nova-core/nova_core.rs b/drivers/gpu/nova-core/nova_core.rs > index cb2bbb30cba1..54505cad4a73 100644 > --- a/drivers/gpu/nova-core/nova_core.rs > +++ b/drivers/gpu/nova-core/nova_core.rs > @@ -2,6 +2,7 @@ > > //! Nova Core GPU Driver > > +mod bitstruct; > mod dma; > mod driver; > mod falcon; > -- > 2.34.1 Reviewed-by: Elle Rhumsaa