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Mon, 12 Oct 2026 11:37:22 +0000 Date: Mon, 12 Oct 2026 19:41:56 +0800 From: Peng Fan To: Andy Shevchenko Cc: Linus Walleij , Bartosz Golaszewski , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Shenwei Wang , linux-gpio@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Peng Fan Subject: Re: [PATCH v6 03/13] gpio: mxc: fix wakeup_pads bit operations Message-ID: References: <20261011-gpio-mxc-cleanup-v6-0-cb47ce2ad758@nxp.com> <20261011-gpio-mxc-cleanup-v6-3-cb47ce2ad758@nxp.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: MA5P287CA0040.INDP287.PROD.OUTLOOK.COM (2603:1096:a01:175::13) To AM8PR04MB7874.eurprd04.prod.outlook.com (2603:10a6:20b:24d::9) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PA4PR04MB7885:EE_|PAXPR04MB8878:EE_ X-MS-Office365-Filtering-Correlation-Id: 72eb330c-eb97-4899-36dc-08df28552ded X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|19092799006|23010399003|376014|7416014|1800799024|366016|6133799003|10067099003|18002099003|22082099003|3023799007|11063799006|4143699003|56012099006; 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So, the above >> >paragraph is incorrect, right? Otherwise it needs to be clarified how >> >assign_bit() does change anything. >> >> I will replace with below: >> >> gpio_set_wake_irq() can be called concurrently for different pins on >> the same port. The IRQ core serializes per irq descriptor, but >> different pins have different descriptors, so concurrent calls for >> pins on the same port run without mutual exclusion. The plain |= and >> &= on wakeup_pads are non-atomic read-modify-write operations that >> can lose updates when two CPUs modify different bits simultaneously. >> Replace them with assign_bit() to make the modifications atomic. > >Right, but the code does change only the writer side. There is no >reader side that was changed. So this patch does *not* add any >atomicity. You also need to check if the reader side already uses >test_bit() or something like that. Otherwise it makes no sense. The writer-vs-writer race is the concern: two concurrent gpio_set_wake_irq() calls for different pins on the same port both do a non-atomic read-modify-write on the same wakeup_pads word. The old |= and &= compile to separate load/modify/store instructions that can interleave, losing one CPU's update. assign_bit() uses an atomic RMW instruction, so concurrent writers to different bits in the same word are safe. The reader side (for_each_set_bit in noirq_suspend, wakeup_pads > 0) runs in noirq context where no concurrent writer can execute, so reader atomicity is not needed. Regards, Peng