From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 E78682517A5; Sat, 14 Mar 2026 13:31:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773495104; cv=none; b=kL8UGPr/XY+R820PFk6tAJ7F/8R/ikytvU6mzn9L4MCqJ+iuVo6GgMm2JBFyL7c+KV2ZqeWIHdCUwhz1eBW0+Ek4usao9ib2yVNdRfNoBa/T5YUe3ryWBifOdozak2ro8kSXOPqqNhOCrpy5ijmc1rvXWxdkpLVJ4D6Y8Uzvoio= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773495104; c=relaxed/simple; bh=33fhq7j5vg+tmMCu8Sapd06qjx9fDJbLUGUc3OjM+E4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rZRxGTmuyUQb86Pbk2Z2/59nHIzcb6nkuricDK9ewLafJMOBgJl+z+N3BE72eSBPzWv5Lz4mxBDw+5ifndHZd4MGhPgjWjQWoC2Zm9mT4UykYcGd6DUxOF7O7A1+7AnHq56ZjUBjeQGmPPVRFH5NhK1puTdcgjFeKWw3y/vvEYw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dv9u0Zpw; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="dv9u0Zpw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3F5EC116C6; Sat, 14 Mar 2026 13:31:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773495103; bh=33fhq7j5vg+tmMCu8Sapd06qjx9fDJbLUGUc3OjM+E4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dv9u0ZpwOCbxh1VMl/0LobIPwxuijRelA04TesVduk5vbbp+kGnqw9UNedhXkOOPt TgOyvngKw842sT462V0uXDzZPJyziLSVipaw4mLC3ezBVhYFy0S4I/UtVix2RzkKKh ROKzexdoLNYAubV50MkEEGhFHovLrU33mKuM81sc= Date: Sat, 14 Mar 2026 14:31:38 +0100 From: Greg Kroah-Hartman To: Markus Probst Cc: Rob Herring , Jiri Slaby , Miguel Ojeda , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , 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 Subject: Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device Message-ID: <2026031447-margarita-untamed-e976@gregkh> References: <20260313-rust_serdev-v3-0-c9a3af214f7f@posteo.de> <20260313-rust_serdev-v3-2-c9a3af214f7f@posteo.de> <2026031402-absence-graph-af5d@gregkh> <2026031422-shaded-matchbook-5078@gregkh> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote: > On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote: > > On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote: > > > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote: > > > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote: > > > > > Add rust private data to `struct serdev_device`, as it is required by the > > > > > rust abstraction added in the following commit > > > > > (rust: add basic serial device bus abstractions). > > > > > > > > why is rust "special" here? What's wrong with the existing private > > > > pointer in this structure? Why must we add another one? > > > Because in rust, the device drvdata will be set after probe has run. In > > > serdev, once the device has been opened, it can receive data. It must > > > be opened either inside probe or before probe, because it can only be > > > configured (baudrate, flow control etc.) and data written to after it > > > has been opened. Because it can receive data before drvdata has been > > > set yet, we need to ensure it waits on data receival for the probe to > > > be finished. Otherwise this would be a null pointer dereference. To do > > > this, we need to store a `Completion` for it to wait and a `bool` in > > > case the probe exits with an error. We cannot store this data in the > > > device drvdata, because this is where the drivers drvdata goes. We also > > > cannot create a wrapper of the drivers drvdata, because > > > `Device::drvdata::()` would always fail in that case. That is why we > > > need a "rust_private_data" for this abstraction to store the > > > `Completion` and `bool`. > > > > So why is this any different from any other bus type? I don't see the > > "uniqueness" here that has not required this to happen for PCI or USB or > > anything else. > > > > What am I missing? > In Short: > In serdev, we have to handle incoming device data (serdev calls on a > function pointer we provide in advance), even in the case that the > driver hasn't completed probe yet. But how is that any different from a USB or PCI driver doing the same thing? Why is serdev so unique here? What specific serdev function causes this and why isn't it an issue with the C api? Can we change the C code to not require this? thanks, greg k-h