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AJvYcCXnqeoWWOrT4EIXm0Zz97fjeDJtpcCbXA1qqCEMhL4d8KmL80g5+WwB8+p2birUvFGsGd2PclPZgMuQQqU=@vger.kernel.org X-Gm-Message-State: AOJu0YyjkbQnknCik7xD2far2PTdiXnZln/faY+t2exUNHC3w87iTtpJ wqR0U3pZZjmycqINM3IR7Lp91W0huO4ioJ+lUfPDoqk3CHRcTEdSvLdM9Y6ADGMLHbvlA7wQ8NV QOQYAHPdoM5FW/c7V2g== X-Google-Smtp-Source: AGHT+IFkqdllbNl34eMzwvx7CHPnSm/L3O6tYExq+epl+LyNuTYeKLR1SA4LPS1EG/NgPCY4RiiyiMddZ+bZ2GI= X-Received: from wmbg1.prod.google.com ([2002:a05:600c:a401:b0:46f:aa50:d718]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600d:6357:b0:46e:3d41:5fe7 with SMTP id 5b1f17b1804b1-47160986ed2mr83729665e9.29.1761142314552; Wed, 22 Oct 2025 07:11:54 -0700 (PDT) Date: Wed, 22 Oct 2025 14:11:53 +0000 In-Reply-To: <20251022.193230.585171330619599845.fujita.tomonori@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251022.193230.585171330619599845.fujita.tomonori@gmail.com> Message-ID: Subject: Re: [PATCH v2 1/2] rust: add udelay() function From: Alice Ryhl To: FUJITA Tomonori Cc: dakr@kernel.org, miguel.ojeda.sandonis@gmail.com, daniel.almeida@collabora.com, a.hindborg@kernel.org, alex.gaynor@gmail.com, ojeda@kernel.org, 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, gregkh@linuxfoundation.org Content-Type: text/plain; charset="utf-8" On Wed, Oct 22, 2025 at 07:32:30PM +0900, FUJITA Tomonori wrote: > On Tue, 21 Oct 2025 17:20:41 +0200 > "Danilo Krummrich" wrote: > > > On Tue Oct 21, 2025 at 5:13 PM CEST, Miguel Ojeda wrote: > >> i.e. if they aren't sure what the value is, then I would prefer they > >> clamp it explicitly on the callee side (or we provide an explicitly > >> clamped version if it is a common case, but it seems to me runtime > >> values are already the minority). > > > > Absolutely! Especially given the context udelay() is introduced > > (read_poll_timeout_atomic()), the compile time checked version is what we really > > want. > > > > Maybe we should even defer a runtime checked / clamped version until it is > > actually needed. > > Then perhaps something like this? > > #[inline(always)] > pub fn udelay(delta: Delta) { > build_assert!( > delta.as_nanos() >= 0 && delta.as_nanos() <= i64::from(bindings::MAX_UDELAY_MS) * 1_000_000 > ); This is a bad idea. Using build_assert! assert for range checks works poorly, as we found for register index bounds checks. If you really want to check it at compile-time, you'll need a wrapper type around Delta that can only be constructed with delays in the right range. Alice