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[180.34.120.7]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7a25f41ad15sm493996b3a.41.2025.10.21.02.27.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Oct 2025 02:27:56 -0700 (PDT) From: FUJITA Tomonori To: dakr@kernel.org, aliceryhl@google.com, daniel.almeida@collabora.com, a.hindborg@kernel.org, alex.gaynor@gmail.com, ojeda@kernel.org Cc: anna-maria@linutronix.de, bjorn3_gh@protonmail.com, boqun.feng@gmail.com, frederic@kernel.org, gary@garyguo.net, jstultz@google.com, linux-kernel@vger.kernel.org, lossin@kernel.org, lyude@redhat.com, rust-for-linux@vger.kernel.org, sboyd@kernel.org, tglx@linutronix.de, tmgross@umich.edu Subject: [PATCH v2 1/2] rust: add udelay() function Date: Tue, 21 Oct 2025 16:11:45 +0900 Message-ID: <20251021071146.2357069-2-fujita.tomonori@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251021071146.2357069-1-fujita.tomonori@gmail.com> References: <20251021071146.2357069-1-fujita.tomonori@gmail.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add udelay() function, inserts a delay based on microseconds with busy waiting, in preparation for supporting read_poll_count_atomic(). Signed-off-by: FUJITA Tomonori --- rust/helpers/time.c | 5 +++++ rust/kernel/time/delay.rs | 37 +++++++++++++++++++++++++++++++++++++ 2 files changed, 42 insertions(+) diff --git a/rust/helpers/time.c b/rust/helpers/time.c index a318e9fa4408..67a36ccc3ec4 100644 --- a/rust/helpers/time.c +++ b/rust/helpers/time.c @@ -33,3 +33,8 @@ s64 rust_helper_ktime_to_ms(const ktime_t kt) { return ktime_to_ms(kt); } + +void rust_helper_udelay(unsigned long usec) +{ + udelay(usec); +} diff --git a/rust/kernel/time/delay.rs b/rust/kernel/time/delay.rs index eb8838da62bc..fb7c15dfe186 100644 --- a/rust/kernel/time/delay.rs +++ b/rust/kernel/time/delay.rs @@ -47,3 +47,40 @@ pub fn fsleep(delta: Delta) { bindings::fsleep(delta.as_micros_ceil() as c_ulong) } } + +/// Inserts a delay based on microseconds with busy waiting. +/// +/// Equivalent to the C side [`udelay()`], which delays in microseconds. +/// +/// `delta` must be within `[0, `MAX_UDELAY_MS`]` in milliseconds; +/// otherwise, it is erroneous behavior. That is, it is considered a bug to +/// call this function with an out-of-range value, in which case the function +/// will insert a delay for at least the maximum value in the range and +/// may warn in the future. +/// +/// The behavior above differs from the C side [`udelay()`] for which out-of-range +/// values could lead to an overflow and unexpected behavior. +/// +/// [`udelay()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.udelay +pub fn udelay(delta: Delta) { + const MAX_UDELAY_DELTA: Delta = Delta::from_millis(bindings::MAX_UDELAY_MS as i64); + + let delta = if (Delta::ZERO..=MAX_UDELAY_DELTA).contains(&delta) { + delta + } else { + // TODO: Add WARN_ONCE() when it's supported. + MAX_UDELAY_DELTA + }; + + // SAFETY: It is always safe to call `udelay()` with any duration. + // Note that the kernel is compiled with `-fno-strict-overflow` + // so any out-of-range value could lead to unexpected behavior + // but won't lead to undefined behavior. + unsafe { + // Convert the duration to microseconds and round up to preserve + // the guarantee; `udelay()` inserts a delay for at least + // the provided duration, but that it may delay for longer + // under some circumstances. + bindings::udelay(delta.as_micros_ceil() as c_ulong) + } +} -- 2.43.0