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Mon, 14 Sep 2026 10:22:05 +0000 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 14 Sep 2026 11:22:03 +0100 Message-Id: Cc: "Matteo Kloiber" , , , , , , , , , , , , , Subject: Re: [PATCH 2/2] rust: scatterlist: honor the device's maximum segment size From: "Gary Guo" To: "Danilo Krummrich" , "Alexandre Courbot" X-Mailer: aerc 0.22.0 References: <20260831233215.287881-1-kernel@matt3o12.de> <20260831233215.287881-3-kernel@matt3o12.de> <20260913210806.125589-1-kernel@matt3o12.de> In-Reply-To: X-ClientProxiedBy: ZR0P278CA0089.CHEP278.PROD.OUTLOOK.COM (2603:10a6:910:22::22) To LOAP265MB8560.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:4ab::19) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LOAP265MB8560:EE_|CWXP265MB2294:EE_ X-MS-Office365-Filtering-Correlation-Id: efcbb828-5013-4fb9-0567-08df124a067d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; ARA:13230040|23010399003|10070799003|366016|7416014|376014|1800799024|10067099003|6133799003|56012099006|22082099003|18002099003|4143699003; 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The correct fix is to make sure that >>>> `dma_set_max_seg_size` is called by the driver, and while we are at it >>>> we also want every driver to call `dma_set_mask_and_coherent`. Ideally >>>> we would use the type system to make sure that both functions are call= ed >>>> before any DMA operation can take place (using a safe interface), but >>>> I'm not quite sure yet how we can do this. >>> >>> This sounds sensible indeed. Should I open a thread regarding that on Z= ulip? >> >> Probably not necessary, the mailing-list has a larger audience and is >> the right place for this. I expect people will jump in here with their >> thoughts. > > The problem with those is not that they must strictly be called before > allocating DMA memory, but they must not be called concurrently with othe= r DMA > operations, such as allocating DMA memory, as it would technically be a d= ata > race. Do they really have to be called *before* allocating DMA memory, not do the= y just need not be called *concurrent* to DMA memory allocation? If it's the former, we can require these to require mutable reference inste= ad, so the probe takes `Pin<&'bound mut Device>>` which still derefs t= o `&'bound Device`, but Rust will require the shared reference to not co-exist with the mutable reference. Best, Gary