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Message-Id: <DD7GCYCZU3P3.1KK174S7MQ5BW@nvidia.com>
Date: Thu, 02 Oct 2025 10:41:22 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Joel Fernandes" <joelagnelf@...dia.com>,
<linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>,
<dri-devel@...ts.freedesktop.org>, <dakr@...nel.org>, <acourbot@...dia.com>
Cc: "Alistair Popple" <apopple@...dia.com>, "Miguel Ojeda"
<ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng"
<boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
<bjorn3_gh@...tonmail.com>, "Benno Lossin" <lossin@...nel.org>, "Andreas
Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
"Trevor Gross" <tmgross@...ch.edu>, "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>, "John Hubbard"
<jhubbard@...dia.com>, "Timur Tabi" <ttabi@...dia.com>,
<joel@...lfernandes.org>, "Elle Rhumsaa" <elle@...thered-steel.dev>, "Yury
Norov" <yury.norov@...il.com>, "Daniel Almeida"
<daniel.almeida@...labora.com>, "Andrea Righi" <arighi@...dia.com>,
<nouveau@...ts.freedesktop.org>
Subject: Re: [PATCH v5 6/9] rust: bitfield: Add KUNIT tests for bitfield
On Tue Sep 30, 2025 at 11:45 PM JST, Joel Fernandes wrote:
> Add KUNIT tests to make sure the macro is working correctly.
>
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> ---
> rust/kernel/bitfield.rs | 321 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 321 insertions(+)
>
> diff --git a/rust/kernel/bitfield.rs b/rust/kernel/bitfield.rs
> index fed19918c3b9..9a20bcd2eb60 100644
> --- a/rust/kernel/bitfield.rs
> +++ b/rust/kernel/bitfield.rs
> @@ -402,3 +402,324 @@ fn default() -> Self {
> }
> };
> }
> +
> +#[::kernel::macros::kunit_tests(kernel_bitfield)]
> +mod tests {
> + use core::convert::TryFrom;
> +
> + // Enum types for testing => and ?=> conversions
> + #[derive(Debug, Clone, Copy, PartialEq)]
> + enum MemoryType {
> + Unmapped = 0,
> + Normal = 1,
> + Device = 2,
> + Reserved = 3,
> + }
> +
> + impl Default for MemoryType {
> + fn default() -> Self {
> + MemoryType::Unmapped
> + }
> + }
Tip: you can add `Default` to the `#[derive]` marker of `MemoryType` and
mark the variant you want as default with `#[default]` instead of
providing a full impl block:
#[derive(Debug, Default, Clone, Copy, PartialEq)]
enum MemoryType {
#[default]
Unmapped = 0,
Normal = 1,
Device = 2,
Reserved = 3,
}
> +
> + impl TryFrom<u8> for MemoryType {
> + type Error = u8;
> + fn try_from(value: u8) -> Result<Self, Self::Error> {
> + match value {
> + 0 => Ok(MemoryType::Unmapped),
> + 1 => Ok(MemoryType::Normal),
> + 2 => Ok(MemoryType::Device),
> + 3 => Ok(MemoryType::Reserved),
> + _ => Err(value),
> + }
> + }
> + }
> +
> + impl From<MemoryType> for u64 {
> + fn from(mt: MemoryType) -> u64 {
> + mt as u64
> + }
> + }
> +
> + #[derive(Debug, Clone, Copy, PartialEq)]
> + enum Priority {
> + Low = 0,
> + Medium = 1,
> + High = 2,
> + Critical = 3,
> + }
> +
> + impl Default for Priority {
> + fn default() -> Self {
> + Priority::Low
> + }
> + }
> +
> + impl From<u8> for Priority {
> + fn from(value: u8) -> Self {
> + match value & 0x3 {
> + 0 => Priority::Low,
> + 1 => Priority::Medium,
> + 2 => Priority::High,
> + _ => Priority::Critical,
> + }
> + }
> + }
> +
> + impl From<Priority> for u16 {
> + fn from(p: Priority) -> u16 {
> + p as u16
> + }
> + }
> +
> + bitfield! {
> + struct TestPageTableEntry(u64) {
> + 0:0 present as bool;
> + 1:1 writable as bool;
> + 11:9 available as u8;
> + 13:12 mem_type as u8 ?=> MemoryType;
> + 17:14 extended_type as u8 ?=> MemoryType; // For testing failures
> + 51:12 pfn as u64;
> + 51:12 pfn_overlap as u64;
> + 61:52 available2 as u16;
> + }
> + }
> +
> + bitfield! {
> + struct TestControlRegister(u16) {
> + 0:0 enable as bool;
> + 3:1 mode as u8;
> + 5:4 priority as u8 => Priority;
> + 7:4 priority_nibble as u8;
> + 15:8 channel as u8;
> + }
> + }
> +
> + bitfield! {
> + struct TestStatusRegister(u8) {
> + 0:0 ready as bool;
> + 1:1 error as bool;
> + 3:2 state as u8;
> + 7:4 reserved as u8;
> + 7:0 full_byte as u8; // For entire register
> + }
> + }
> +
> + #[test]
> + fn test_single_bits() {
> + let mut pte = TestPageTableEntry::default();
> +
> + assert!(!pte.present());
> + assert!(!pte.writable());
> +
> + pte = pte.set_present(true);
> + assert!(pte.present());
> +
> + pte = pte.set_writable(true);
> + assert!(pte.writable());
> +
> + pte = pte.set_writable(false);
> + assert!(!pte.writable());
> +
> + assert_eq!(pte.available(), 0);
> + pte = pte.set_available(0x5);
> + assert_eq!(pte.available(), 0x5);
I'd suggest testing the actual raw value of the register on top of
invoking the getter. That way you also test that:
- The right field is actually written (i.e. if the offset is off by one,
the getter will return the expected result even though the bitfield
has the wrong value),
- No other field has been affected.
So something like:
pte = pte.set_present(true);
assert!(pte.present());
assert(pte.into(), 0x1u64);
pte = pte.set_writable(true);
assert!(pte.writable());
assert(pte.into(), 0x3u64);
It might look a bit gross, but it is ok since these are not doctests
that users are going to take as a reference, so we case improve test
coverage at the detriment of readability.
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