From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailout1.w1.samsung.com (mailout1.w1.samsung.com [210.118.77.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 444A02E0410 for ; Thu, 21 Aug 2025 22:35:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=210.118.77.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755815746; cv=none; b=nwUmKVghOKy3K78cEV9vY2OMRAHX+qFAVPuZXSg/tV0bniPdbv+VcSW6GRI0Cs+ps9LIieZeW3Z7En9XfPXApg+PEZFdM5X1RlFuFAZ1oV3Mj2Oun+N03Y83XjVZ6TIc/uiV/4ctQsW9/cZIJ5s9++b57bh2GcKuhncFWr03dYI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755815746; c=relaxed/simple; bh=FkxrYII2TEEj7Hu4cK1rRwgXY6zqhrRnMGhlROYpvDo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:From:In-Reply-To: Content-Type:References; b=R56VKtpY15qN2tNptllJm7/1Y3HDqTr723UFnbCB9cqkMJSv6xBx5Ogg7MIquTtCrxBofuqah4Cn5kqQsfvRYPWVz/xTGbeiDvbHqjnyoyrWjveJ+7VEHPnx8PFe1UwdzjrdBnES8LuQddv0y8FnjdKMTD0HGHXsVjSmVhcmwNY= ARC-Authentication-Results:i=1; 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d=samsung.com; s=mail20170921; t=1755815741; bh=3i+hbzU8RFcDzVjqMTUidVYvZwJLP627miUufKiWjKc=; h=Date:Subject:To:Cc:From:In-Reply-To:References:From; b=EchqXJIdjhi1/Rw0fXBY4CmZy/EKm7bSiCYPGO6TfZECD3oYg/iML48fWFfMqa3I7 t2wIHPc19loWlcJZJcWdc/4W1E7qVDkq6Nq5nGrRRsmjeCZS1vxbybhe+tp0+ol05T dxyzlS99qMR05oryn84X5fjsF8q8XCW5bIWMish4= Received: from eusmtip2.samsung.com (unknown [203.254.199.222]) by eucas1p2.samsung.com (KnoxPortal) with ESMTPA id 20250821223540eucas1p2887283df2fcd024bb24a0034bebb99ce~d6Rzr2R6r0984009840eucas1p2k; Thu, 21 Aug 2025 22:35:40 +0000 (GMT) Received: from [192.168.1.44] (unknown [106.210.136.40]) by eusmtip2.samsung.com (KnoxPortal) with ESMTPA id 20250821223539eusmtip2f1a4ec8a2273c2e74d641e183d0914e9~d6RynamBV3047330473eusmtip2H; Thu, 21 Aug 2025 22:35:38 +0000 (GMT) Message-ID: <78ffebda-744b-4a1b-9676-82f46c2d29d1@samsung.com> Date: Fri, 22 Aug 2025 00:35:38 +0200 Precedence: bulk X-Mailing-List: linux-pwm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v14 3/7] rust: pwm: Add complete abstraction layer To: Elle Rhumsaa Cc: =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Guo Ren , Fu Wei , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Marek Szyprowski , Benno Lossin , Michael Turquette , Drew Fustini , Daniel Almeida , linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org Content-Language: en-US From: Michal Wilczynski In-Reply-To: Content-Transfer-Encoding: 7bit X-CMS-MailID: 20250821223540eucas1p2887283df2fcd024bb24a0034bebb99ce X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20250820083544eucas1p233f8b8f7d1c0b59acededa3572d632aa X-EPHeader: CA X-CMS-RootMailID: 20250820083544eucas1p233f8b8f7d1c0b59acededa3572d632aa References: <20250820-rust-next-pwm-working-fan-for-sending-v14-0-df2191621429@samsung.com> <20250820-rust-next-pwm-working-fan-for-sending-v14-3-df2191621429@samsung.com> On 8/20/25 23:11, Elle Rhumsaa wrote: >> +/// Wrapper for a PWM device [`struct pwm_device`](srctree/include/linux/pwm.h). >> +#[repr(transparent)] >> +pub struct Device(Opaque); >> + >> +impl Device { >> + /// Creates a reference to a [`Device`] from a valid C pointer. >> + /// >> + /// # Safety >> + /// >> + /// The caller must ensure that `ptr` is valid and remains valid for the lifetime of the >> + /// returned [`Device`] reference. >> + pub(crate) unsafe fn from_raw<'a>(ptr: *mut bindings::pwm_device) -> &'a Self { >> + // SAFETY: The safety requirements guarantee the validity of the dereference, while the >> + // `Device` type being transparent makes the cast ok. >> + unsafe { &*ptr.cast::() } >> + } > > This looks like the only constructor for `Device`, and it has restricted > visibility. > > Would it be helpful to provide a doc-test here to show intended usage? > > After looking at the C code, it looks like the raw `pwm_device` pointer > is extracted from a `device` struct, or stored in an array of > `pwm_device` pointers. > > Is the intent that the `pwm_device` will always be allocated from C > code? For example, is a `pub fn new() -> &'a Self`-style constructor > not possible/desired? > You're correct the intent is for pwm_device to be allocated and managed by the C core. The Rust code only ever receives a raw pointer to an existing device during callbacks. For this reason, a public new() constructor isn't appropriate, and the from_raw function is pub(crate) for use only by the FFI adapter. A doc-test is also impractical since we can't create a valid pwm_device in a test environment. > Reviewed-by: Elle Rhumsaa > Best regards, -- Michal Wilczynski