From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 F1AE53B7B71; Fri, 26 Jun 2026 18:37:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782499034; cv=none; b=AyiZQVY50pd7Hx+V7KGQfSOaCmScxcJXeo3o9/mkIZSYPm5CrUV+qw2miPQw0q1LkMvpCOHZHqZN1ico/si/cBe92lfgFEJgj5KhD1QtNz6LHJwDCH8CqZOvW87RtAArYubmwbiECtItb2OsVT6TTUsoz6TOitYmScdzrtRKNsQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782499034; c=relaxed/simple; bh=1bY71DPZENvERXkhelA2ESYi7XUBroQQuXZVvVqMMFE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=aRXBIU9Fu5772LjfQDptw+V8h7WbFyXbThA88S1SX2gVaq4MKKDGam14mXI5GrP24te7/DiU6G7JYrGz6vfUszIJXtzCOgq+jxvEobi0dwGPyPHdpR+k6GncxykGwujD2aYWw7VwIMxulW+kU6Y7VNB6YqdCPoegSoEDDkASIyY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=REMzAVBD; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="REMzAVBD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A03011F00A3A; Fri, 26 Jun 2026 18:37:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782499032; bh=LdNaTTk9wNNpDOVSF33kTh+EjW3VqsNef7eZ4WrstEk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=REMzAVBD9Y+oXmHdfOvfnAtazgm3pDPF2DQm/fpdyrA2UK/bEnU0ZyawWhgVTsjX0 0mBFW6JrGflTz4eIIbGBWjafY4kGXt3YRnu05IAEV/bw7XAvxtMOksvAofxUuXB1bd Bg2GWS3/t/32FjWKvvfdOl0F8EhAy0S9SyDR1NzPp61TudiXZWFGiGEO38fD8X8nxR EOT2+jyTv6lAfzXAOtTkV0M6Ns0Ujyj0WwMNC2pncWaA2q+0Y+dbyuXBpYqWdY1YXx mOtvYOfUgwu8L+eCkrL6DUsRfez/k8ReZU7F93EKTfLW6EAy5yHSWK+1fCOeIM2yd3 CHhYtrCqeYdUg== From: Danilo Krummrich To: gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, ojeda@kernel.org, boqun@kernel.org, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, acourbot@nvidia.com, ecourtney@nvidia.com, m.wilczynski@samsung.com, david.m.ertman@intel.com, ira.weiny@intel.com, leon@kernel.org, daniel.almeida@collabora.com, bhelgaas@google.com, kwilczynski@kernel.org Cc: driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, nova-gpu@lists.linux.dev, dri-devel@lists.freedesktop.org, linux-pwm@vger.kernel.org, rust-for-linux@vger.kernel.org Subject: [PATCH v4 6/7] rust: pci: return DevresLt from Bar::into_devres() Date: Fri, 26 Jun 2026 20:36:13 +0200 Message-ID: <20260626183630.2585057-7-dakr@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260626183630.2585057-1-dakr@kernel.org> References: <20260626183630.2585057-1-dakr@kernel.org> 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 Implement ForLt and CovariantForLt for Bar<'static, SIZE> so that DevresLt can shorten the stored 'static lifetime back to the caller's borrow lifetime. CovariantForLt is sound because Bar<'a, SIZE> only holds &'a Device, which is covariant over 'a. Since DevresLt::new() handles the lifetime transmutation internally, into_devres() no longer needs an explicit transmute to Bar<'static>. Add a DevresBar type alias for convenience. Reviewed-by: Alexandre Courbot Signed-off-by: Danilo Krummrich --- rust/kernel/pci.rs | 1 + rust/kernel/pci/io.rs | 37 ++++++++++++++++++++++++++----------- 2 files changed, 27 insertions(+), 11 deletions(-) diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs index 5071cae6543f..f783b9d9fa26 100644 --- a/rust/kernel/pci.rs +++ b/rust/kernel/pci.rs @@ -45,6 +45,7 @@ ConfigSpace, ConfigSpaceKind, ConfigSpaceSize, + DevresBar, Extended, Normal, // }; diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs index 0461e01aaa20..7a0d2d74129d 100644 --- a/rust/kernel/pci/io.rs +++ b/rust/kernel/pci/io.rs @@ -6,7 +6,7 @@ use crate::{ bindings, device, - devres::Devres, + devres::DevresLt, io::{ Io, IoCapable, @@ -14,7 +14,11 @@ Mmio, MmioRaw, // }, - prelude::*, // + prelude::*, + types::{ + CovariantForLt, + ForLt, // + }, // }; use core::{ marker::PhantomData, @@ -151,6 +155,19 @@ pub struct Bar<'a, const SIZE: usize = 0> { num: i32, } +impl ForLt for Bar<'static, SIZE> { + type Of<'a> = Bar<'a, SIZE>; +} + +// SAFETY: `Bar<'a, SIZE>` is covariant over `'a`; it holds `&'a Device`, +// which is covariant. +unsafe impl CovariantForLt for Bar<'static, SIZE> {} + +/// A device-managed PCI BAR mapping. +/// +/// See [`Bar::into_devres`]. +pub type DevresBar = DevresLt>; + impl<'a, const SIZE: usize> Bar<'a, SIZE> { pub(super) fn new( pdev: &'a Device, @@ -223,15 +240,13 @@ fn release(&self) { /// Consume the `Bar` and register it as a device-managed resource. /// - /// The returned `Devres>` can outlive the original lifetime `'a`. Access - /// to the BAR is revoked when the device is unbound. - pub fn into_devres(self) -> Result>> { - // SAFETY: Casting to `'static` is sound because `Devres` guarantees the `Bar` does not - // actually outlive the device -- access is revoked and the resource is released when the - // device is unbound. - let bar: Bar<'static, SIZE> = unsafe { core::mem::transmute(self) }; - let pdev = bar.pdev; - Devres::new(pdev.as_ref(), bar) + /// The returned [`DevresBar`] can outlive the original borrow and be stored in driver data. + /// Access to the BAR is revoked automatically when the device is unbound. + pub fn into_devres(self) -> Result> { + let pdev = self.pdev; + // SAFETY: `Bar` only holds a reference to the device and an I/O mapping, both of which + // remain valid for the device's full bound scope, not just for `'a`. + unsafe { DevresLt::new(pdev.as_ref(), self) } } } -- 2.54.0