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 5E4F5CD6E56 for ; Sun, 31 May 2026 19:42:28 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 8ED7710E1E2; Sun, 31 May 2026 19:42:27 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; secure) header.d=posteo.de header.i=@posteo.de header.b="owDtBQDL"; dkim-atps=neutral Received: from mout01.posteo.de (mout01.posteo.de [185.67.36.65]) by gabe.freedesktop.org (Postfix) with ESMTPS id 3BD1B10E1E2 for ; Sun, 31 May 2026 19:42:25 +0000 (UTC) Received: from submission (posteo.de [185.67.36.169]) by mout01.posteo.de (Postfix) with ESMTPS id 56AB2240029 for ; Sun, 31 May 2026 21:42:22 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=posteo.de; s=2017; t=1780256542; bh=hUSWLp5mi7L5MOKZrN3iLNpIOwJb8J5/4ZNT2N3R2ww=; h=Message-ID:Subject:From:To:Cc:Date:Autocrypt:Content-Type: MIME-Version:OpenPGP:From; b=owDtBQDLgsKiOMwEXQi/IAIQCjwA+Mqa/23jbm94R7/6pOWMci10NYImeUg9+ZqOh hSTeeMChegEgibluJl0M5AYfLA03DvUI4zALnx++jSJpn/0n+w7nyOTJOvbgHBmu3w /g2MllJ4PJ3DVODZbQNDq8FVdFD7B/lAqrfZuC/bUsvez23YPKBR6llHk8FLFWrrlt 5mw9Y+msoVUySj1+r0yIPFFeDWNJuGKlRIjbWSSKpsJOK9m6SzWSSnFf2EHb1BVhZU +OnxNhzKryONTUSNs2j7CTYDMXVkAz5sqCtaGQe/ZSM4jKM4SuDYgdnE8MASFrz8Cd AhGQCHXHyYjSw== Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4gT6tg2ngKz6tyt; Sun, 31 May 2026 21:42:19 +0200 (CEST) Message-ID: <12fa6237168ecf6dc65ebf46118beeb5c51f3d1c.camel@posteo.de> Subject: Re: [PATCH v11 1/3] rust: add basic serial device bus abstractions From: Markus Probst To: Danilo Krummrich , Markus Probst via B4 Relay Cc: Rob Herring , Greg Kroah-Hartman , Jiri Slaby , Miguel Ojeda , Gary Guo , =?ISO-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Kari Argillander , "Rafael J. Wysocki" , Viresh Kumar , Boqun Feng , David Airlie , Simona Vetter , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-pm@vger.kernel.org, driver-core@lists.linux.dev, dri-devel@lists.freedesktop.org Date: Sun, 31 May 2026 19:42:21 +0000 In-Reply-To: References: <20260531-rust_serdev-v11-0-dee8e0d830f1@posteo.de> <20260531-rust_serdev-v11-1-dee8e0d830f1@posteo.de> Autocrypt: addr=markus.probst@posteo.de; prefer-encrypt=mutual; keydata=mQINBGiDvXgBEADAXUceKafpl46S35UmDh2wRvvx+UfZbcTjeQOlSwKP7YVJ4JOZrVs93 qReNLkOWguIqPBxR9blQ4nyYrqSCV+MMw/3ifyXIm6Pw2YRUDg+WTEOjTixRCoWDgUj1nOsvJ9tVA m76Ww+/pAnepVRafMID0rqEfD9oGv1YrfpeFJhyE2zUw3SyyNLIKWD6QeLRhKQRbSnsXhGLFBXCqt 9k5JARhgQof9zvztcCVlT5KVvuyfC4H+HzeGmu9201BVyihJwKdcKPq+n/aY5FUVxNTgtI9f8wIbm fAjaoT1pjXSp+dszakA98fhONM98pOq723o/1ZGMZukyXFfsDGtA3BB79HoopHKujLGWAGskzClwT jRQxBqxh/U/lL1pc+0xPWikTNCmtziCOvv0KA0arDOMQlyFvImzX6oGVgE4ksKQYbMZ3Ikw6L1Rv1 J+FvN0aNwOKgL2ztBRYscUGcQvA0Zo1fGCAn/BLEJvQYShWKeKqjyncVGoXFsz2AcuFKe1pwETSsN 6OZncjy32e4ktgs07cWBfx0v62b8md36jau+B6RVnnodaA8++oXl3FRwiEW8XfXWIjy4umIv93tb8 8ekYsfOfWkTSewZYXGoqe4RtK80ulMHb/dh2FZQIFyRdN4HOmB4FYO5sEYFr9YjHLmDkrUgNodJCX CeMe4BO4iaxUQARAQABtCdNYXJrdXMgUHJvYnN0IDxtYXJrdXMucHJvYnN0QHBvc3Rlby5kZT6JAl QEEwEIAD4CGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AWIQSCdBjE9KxY53IwxHM0dh/4561 D0gUCaIZ9HQIZAQAKCRA0dh/4561D0pKmD/92zsCfbD+SrvBpNWtbit7J9wFBNr9qSFFm2n/65qen NNWKDrCzDsjRbALMHSO8nigMWzjofbVjj8Nf7SDcdapRjrMCnidS0DuW3pZBo6W0sZqV/fLx+AzgQ 7PAr6jtBbUoKW/GCGHLLtb6Hv+zjL17KGVO0DdQeoHEXMa48mJh8rS7VlUzVtpbxsWbb1wRZJTD88 ALDOLTWGqMbCTFDKFfGcqBLdUT13vx706Q29wrDiogmQhLGYKc6fQzpHhCLNhHTl8ZVLuKVY3wTT+ f9TzW1BDzFTAe3ZXsKhrzF+ud7vr6ff9p1Zl+Nujz94EDYHi/5Yrtp//+N/ZjDGDmqZOEA86/Gybu 6XE/v4S85ls0cAe37WTqsMCJjVRMP52r7Y1AuOONJDe3sIsDge++XFhwfGPbZwBnwd4gEVcdrKhnO ntuP9TvBMFWeTvtLqlWJUt7n8f/ELCcGoO5acai1iZ59GC81GLl2izObOLNjyv3G6hia/w50Mw9MU dAdZQ2MxM6k+x4L5XeysdcR/2AydVLtu2LGFOrKyEe0M9XmlE6OvziWXvVVwomvTN3LaNUmaINhr7 pHTFwDiZCSWKnwnvD2+jA1trKq1xKUQY1uGW9XgSj98pKyixHWoeEpydr+alSTB43c3m0351/9rYT TTi4KSk73wtapPKtaoIR3rOFHLQXbWFya3VzLnByb2JzdEBwb3N0ZW8uZGWJAlEEEwEIADsWIQSCd BjE9KxY53IwxHM0dh/4561D0gUCaIO9eAIbAwULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgAAKCR A0dh/4561D0oHZEACEmk5Ng9+OXoVxJJ+c9slBI2lYxyBO84qkWjoJ/0GpwoHk1IpyL+i+kF1Bb7y Hx9Tiz8ENYX7xIPTZzS8hXs1ksuo76FQUyD6onA/69xZIrYZ0NSA5HUo62qzzMSZL7od5e12R6OPR lR0PIuc4ecOGCEq3BLRPfZSYrL54tiase8HubXsvb6EBQ8jPI8ZUlr96ZqFEwrQZF/3ihyV6LILLk geExgwlTzo5Wv3piOXPTITBuzuFhBJqEnT25q2j8OumGQ+ri8oVeAzx24g1kc11pwpR0sowfa5MvZ WrrBcaIL7uJfR/ig7FyGnTQ1nS3btf3p0v8A3fc4eUu/K2No3l2huJp3+LHhCmpmeykOhSB63Mj3s 3Q87LD0HE0HBkTEMwp+sD97ZRpO67H5shzJRanUaDTb/mREfzpJmRT1uuec0X2zItL7a6itgMJvYI KG29aJLX3fTzzVzFGPgzVZYEdhu4y53p0qEGrrC1JtKR6DRPE1hb/OdWOkjmJ75+PPLD9U5IuRd6y sHJWsEBR1F0wkMPkEofWsvMYJzWXx/rvTWO8N4D6HigTgBXAXNgbc3IHpHlkvKoBJptv6DRVRtIrz 0G0cfBY0Sm7he4N2IYDWWdGnPBZ3rlLSdj5EiBU2YWgIgtLrb8ZNJ3ZlhYluGnBJDGRqy2jC9s1jY 66sLA9rQZMHhJTzMyIDwweGlvMzJAcG9zdGVvLmV1PokCbQQTAQgAVxYhBIJ0GMT0rFjncjDEczR2 H/jnrUPSBQJpa71VGxSAAAAAAAQADm1hbnUyLDIuNSsxLjExLDIsMgIbAwULCQgHAgIiAgYVCgkIC wIEFgIDAQIeBwIXgAAKCRA0dh/4561D0gKJD/9uOQKYlsDoQX65Gd0LiMT0C+5vXgr3VI0PHDOwcv 51fJ3A1vNyPZRFPGrz8+mDEXUQOF/INfnz5Tu1QHwf+iYcWcTGAN/FHgVR6ET6VBNU2hJaKhu+Ggo kjYyJTOvyX+3yNRUfSny0GjTjIPuPTErjqmHF+BtjXslpgwqnNMznf3lRIuUjRORupos6p3k1DndE 5vzUTmXSvMyXyOD2KhBl/kL76k0bHYyAQytZPag12pltrtFbA/r2phDGN2si8PooDT99bSTJjaM45 MTAAHbHKJfvgfK41bNFD5mMtpWpL195XRtS0Nrxdg3PaYBxN5gtTG0RyZfpYRlkdEhm+jj/8RxuSG i/qdhRdbiI7K2IELWeQVHSNDi9JabR/UzlR4NSnhfAjRIVlRM+eFbUl8XwxwVrAkojF5IraH2qRvg VCmuFsHUW07FUlrDrzpjXsD73cKppoFGDCdDR0BHJepXbFLS9+AqkT+guRJlnCTg2p+TQtnbwPgKp Vj98JixovCl99zRYTsL2bRNU5+q8iET65VMJ1ydyNanvLd5vI/NqDkXhlXLsGmdaDTtu4R21PkToX dQNGrZ91M9nlIBKw8Y7c7xZ4098qX2b8JX/CxD+gC1r4C8vuA3GkhFLx+KlkON7LyiJPkrePp6Qky jfGillcaQOqFZ3WwVqyzG1BUfTow== Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-i+uPwUkDiLZ5y8MtsrTf" MIME-Version: 1.0 OpenPGP: url=https://posteo.de/keys/markus.probst@posteo.de.asc; preference=encrypt 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" --=-i+uPwUkDiLZ5y8MtsrTf Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2026-05-31 at 01:51 +0200, Danilo Krummrich wrote: > On Sun May 31, 2026 at 12:51 AM CEST, Markus Probst via B4 Relay wrote: > > +#[pinned_drop] > > +impl PinnedDrop for PrivateData<'_, T> { > > + fn drop(self: Pin<&mut Self>) { > > + let mut active =3D self.active.lock(); > > + if *active { > > + // SAFETY: > > + // - We have exclusive access to `self.driver`. > > + // - `self.driver` is guaranteed to be initialized. > > + unsafe { (*self.driver.get()).assume_init_drop() }; > > + *active =3D false; > > + } > > + > > + // SAFETY: We have exclusive access to `self.open`. > > + if unsafe { *self.open.get() } { > > + // SAFETY: `self.sdev.as_raw()` is guaranteed to be a poin= ter to a valid > > + // `struct serdev_device`. > > + unsafe { bindings::serdev_device_close(self.sdev.as_raw())= }; > > + } > > + } > > +} >=20 > Just in case it came across otherwise, I did not mean to push for you to = go for > this approach. We just kept discussing it because it let to the (to me mo= re > interesting) discussion around the LED class device abstraction. >=20 > While this approach gets us rid of an extra allocation and the rust_priva= te_data > pointer in struct serdev_device it also turns out a bit more convoluted. >=20 > That said, both are correct, and I won't object either one; up to you and= the > serdev / tty maintainers. >=20 > Please wait a bit before resending, so other people can comment on this a= s well. >=20 > > + extern "C" fn receive_buf_callback( > > + sdev: *mut bindings::serdev_device, > > + buf: *const u8, > > + length: usize, > > + ) -> usize { > > + // SAFETY: The serial device bus only ever calls the receive b= uf callback with a valid > > + // pointer to a `struct serdev_device`. > > + // > > + // INVARIANT: `sdev` is valid for the duration of `receive_buf= _callback()`. > > + let sdev =3D unsafe { &*sdev.cast::>>() }; >=20 > CoreInternal snuck back in, should be BoundInternal. >=20 > > + > > + // SAFETY: `receive_buf_callback` is only ever called after a = successful call to > > + // `probe_callback`, hence it's guaranteed that `Device::set_d= rvdata()` has been called > > + // and stored a `Pin>>`. > > + let private_data =3D unsafe { sdev.as_ref().drvdata_borrow::>() }; > > + let active =3D private_data.active.lock(); >=20 > I think SRCU would be a much better fit, but the code didn't land yet, so= the > mutex seems fine for now. But I'd probably add a TODO. I just noticed, is it even possible to use SRCU here? Currently the mutex not only ensures that no drvdata access happens after drvdata drop, but also that the receive_buf waits for the probe to complete, as the drvdata hasn't been initialized yet. (drvdata refers to PrivateData.driver in this context, not the whole PrivateData) Thanks - Markus Probst >=20 > > + > > + if !*active { > > + return length; > > + } > > + > > + // SAFETY: No one has exclusive access to `private_data.driver= `. > > + let data =3D unsafe { &*private_data.driver.get() }; > > + // SAFETY: > > + // - `private_data.driver` is pinned. > > + // - `receive_buf_callback` is only ever called after a succes= sful call to `probe_callback`, > > + // hence it's guaranteed that `private_data.driver` was init= ialized. > > + let data_pinned =3D unsafe { Pin::new_unchecked(data.assume_in= it_ref()) }; > > + > > + // SAFETY: `buf` is guaranteed to be non-null and has the size= of `length`. > > + let buf =3D unsafe { core::slice::from_raw_parts(buf, length) = }; > > + > > + T::receive(sdev, data_pinned, buf) > > + } > > +} --=-i+uPwUkDiLZ5y8MtsrTf Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQJPBAABCAA5FiEEgnQYxPSsWOdyMMRzNHYf+OetQ9IFAmocjxobFIAAAAAABAAO bWFudTIsMi41KzEuMTIsMiwyAAoJEDR2H/jnrUPSpGMQALexWGRaLmUISqGonZYw CeOMrMEudQuPoIAC1NbyIgnpT3ir0TLAP0G5nEwbQDKSeB3syHQqjEB8wMYaYjHX RUFlkm1ITINn5Yc3Pj0gL6FI3RC96G/1NZjtDhLxct+qeYzovYfe5ECfU6Cch65c H2LCNtBQdLOWc//PCXrz7gX6HYZnv4pGVlZrWxxvDLt21MFCAKJEpt+xDvIkU+BK KX40c+lHqUNNlafCLiZnKTGw6XusWT6ziCN8OaQcCLkbhXKIoka1rSQh6e40HNRG S7Cjj4o/8ix5JLmURMpNXtxUV2G51F9St9oG/iGYIuwMxwRA5HdRFoats9NwdSa9 GLrhaCdaqJ3awv57Bp+k/HVCG6pta0KkNs/BPbHQ2dtkHNCn5d7QZk3IZ2ilU/pY qrAqDMylJc2gCRoQqhQKZRk9XMZ1iubnHUEojgEJGH1Eo0zf72R6IIVvAN5/3gZI RaAbCMzYr7Fnt0eQf0I8VIpkSf6EcfOeD0IVkGiEsqA64h0fM/XFeuXMa7i7Mwhv LDvHWpQWpknQ3SpwuMkgpMOUkqmpmrCjJ8PEtofApBxCigw0jyzVfR783WE3Xvhg r+f+Lvm5kiBMp9Whdqg74ybQ/w4MRjC42y8bQ9bOdfinP5+7mTOimsDvMADhcLbM rchoKeYTBB0SYYICElpnVTmL =ADNr -----END PGP SIGNATURE----- --=-i+uPwUkDiLZ5y8MtsrTf--