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 X-Spam-Level: X-Spam-Status: No, score=-7.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MSGID_FROM_MTA_HEADER,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 77B1DC433B4 for ; Mon, 26 Apr 2021 04:34:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 588D661363 for ; Mon, 26 Apr 2021 04:34:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231667AbhDZEfE (ORCPT ); Mon, 26 Apr 2021 00:35:04 -0400 Received: from mail-eopbgr30130.outbound.protection.outlook.com ([40.107.3.130]:37653 "EHLO EUR03-AM5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S229469AbhDZEe7 (ORCPT ); Mon, 26 Apr 2021 00:34:59 -0400 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=YfOCyHvhqS2pOOGhYeNGbkjTU8FV5PRBYLM6+2qzT0NUqFLBW3pxymcww0ktTAAIsIs+awhyFXisKhcgIQ+60Noa4bA078qPizTIM0Rl/P6JvHJ+zHUV/XbidOgfzVRT/w638ydPFHJR2qJ28d3TuCWuGo4ZA+XzfIQeiZSuPOjKWpkO10aew12stlfAF/nLAWoZqIYpxkbPpwtVKGcG3QhXDYfHH4WyWDegIj3DzZ34InTMUOXErl5ZCwfmWkZT4e+SFxesLSnTz5cH5HkDviK1VQhDZ1zNaSi8GvxSKHHqkn9hEKXbVGJ37NdDKQ85yfdRmWHcbSCPBvbAAsUCPA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=IGqF/lpSoQskkOnt7MAit3sKQ443fnktX16c8pRviPI=; b=kmVeCtKEugz00H1PnsRqVYlImP2uvhM8U9HeP5aZG5pzobyGiNIsSy8x6bGVLHR5kwQnxvvXBegFlpkBI86N1MT7vHfyxhFI/0f0xpKsh7VYI9O+ToZKZDmbEHbd6uX8ENbuDGLreElqDdiWQh1tHz8nxQ729pweveBPk1LCKvIKA1B3lwHkxaA/PybkWvGojaBKoDQO4qt/zHLRzGuAzXkfAy9Z35HF6fxWh2QCKBPZJTgNhoR6gHO/qsU3TS2k0cLcgbB2teeN1FYVvF7SN1uY33j5kF+WnVTVNyaFkj6A4K0PiP8IetDdK8lLM8AQ2zLypsy/dyVnVoB31cDsGA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=axentia.se; dmarc=pass action=none header.from=axentia.se; dkim=pass header.d=axentia.se; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=axentia.se; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=IGqF/lpSoQskkOnt7MAit3sKQ443fnktX16c8pRviPI=; b=f1Vr4xDytU8Oy2DEMopKldYF6oVg65BGzkyAHPsTBqxjb0nwa+hRlNpHw0seBk7f66We0PxFVbsF5srl08ElyojtVyAnpWu2mdcHuRv6G1Z3xFlSafGxbuvlBmv1VlpWSlSHOkADMfFsisQZDrl7UXQmlRH60GmtM1KMNvpPckg= Authentication-Results: vger.kernel.org; dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=none action=none header.from=axentia.se; Received: from DB8PR02MB5482.eurprd02.prod.outlook.com (2603:10a6:10:eb::29) by DB8PR02MB5849.eurprd02.prod.outlook.com (2603:10a6:10:f8::23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4065.21; Mon, 26 Apr 2021 04:34:15 +0000 Received: from DB8PR02MB5482.eurprd02.prod.outlook.com ([fe80::d47d:ca8c:4fe6:3908]) by DB8PR02MB5482.eurprd02.prod.outlook.com ([fe80::d47d:ca8c:4fe6:3908%3]) with mapi id 15.20.4065.026; Mon, 26 Apr 2021 04:34:15 +0000 Subject: Re: [libgpiod] Request an output line, without modifying the value To: Kent Gibson Cc: "linux-gpio@vger.kernel.org" References: <6e26b4e5-277b-459f-29e7-7eb7e949e6a5@axentia.se> <20210424062132.GA14885@sol> From: Peter Rosin Organization: Axentia Technologies AB Message-ID: Date: Mon, 26 Apr 2021 06:34:12 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 In-Reply-To: <20210424062132.GA14885@sol> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [85.229.94.233] X-ClientProxiedBy: HE1PR09CA0051.eurprd09.prod.outlook.com (2603:10a6:7:3c::19) To DB8PR02MB5482.eurprd02.prod.outlook.com (2603:10a6:10:eb::29) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.13.3] (85.229.94.233) by HE1PR09CA0051.eurprd09.prod.outlook.com (2603:10a6:7:3c::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4065.21 via Frontend Transport; Mon, 26 Apr 2021 04:34:15 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 0d821ff7-040c-44ab-94c2-08d9086c8c69 X-MS-TrafficTypeDiagnostic: DB8PR02MB5849: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:4714; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DB8PR02MB5482.eurprd02.prod.outlook.com;PTR:;CAT:NONE;SFS:(376002)(366004)(346002)(39830400003)(136003)(396003)(316002)(8936002)(16576012)(4326008)(8676002)(86362001)(83380400001)(31696002)(478600001)(6486002)(6666004)(186003)(16526019)(6916009)(53546011)(26005)(66946007)(66476007)(38100700002)(31686004)(36756003)(66556008)(4744005)(956004)(2616005)(36916002)(5660300002)(2906002)(45980500001)(43740500002);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?ODM5bXc5M1Q3a0NtTHg3b29DN0NaYzFYZ0Vqai9rTDFwbTZKN3ovNWVTWUM0?= =?utf-8?B?c2hENkFEZVBHVC9zdDE1NFZrdEJBYXcwNHkwVzJFbk0zb01KUVBuSnhqcllz?= =?utf-8?B?UzNGcWJmVDJnUjJjOWhNLzdDTnBWV2hxSE96aUhKYkhoYVM2MmtETjRnK21E?= =?utf-8?B?VFgyc3ZOUzBmRTZ6RTNwUW00VE1uVjdobTRneDRac3RON0FBeVBsYklsNGFW?= =?utf-8?B?ZnhOR3A4Q0MxNUIwUWZvRStsUFprQm5PTk1NemVvUFB2T2E1MWg2cGs4Z2J1?= =?utf-8?B?enFCS3ZuZ0tQejVDbHJCMWM2ZWpleit6UjkwcU94UjNadU1EZmhGT3E1d0dG?= =?utf-8?B?WnVmRk45U1p6YUtYcW8wa0s5VEtMa0xPZVVobSt4Um5lYTZhcEJFcnNxVENH?= =?utf-8?B?WGF4Yi9xTzJleG9mN0k4K0pYZ2l0REFwc1N1eFNvUG0vQ0JKZ3Q5Q3lCdGtB?= =?utf-8?B?cFpPdGdwMnRiSGgwb1UwblZWVEV3dWw4K0RpcGx5NHJlVml4RnJ0bmhhWnZY?= =?utf-8?B?L2w0SlB5UXFFMkFBSzl0eUNWUFhleWV3SytyeU9qMlBneHR6cDVSMnVSNmMy?= =?utf-8?B?Y0lTcHk5Tlp0TUNPdXlSRjFya0hKM3lMcnpiV3k4ZmJyN2toa2NUU1FlZmhu?= =?utf-8?B?Z0VhQ3VzVWo3eDMzdEg2N2NQVzdsWVp1RkZ0ZDJ4WHpIVkQrQjkyaUtSck53?= =?utf-8?B?OWxSVVE4ZkVJOEhCek1LMk5Za3l6amJ0STlJVzZ1dFJKd2lobEhMcDc0ZzRR?= =?utf-8?B?M3dwV0ZOa0V0cUNJV2VGWk11TzZWcE1Eak5kSDk2TWM4SFJrQURqUjRSNVFK?= =?utf-8?B?SVQrOHpSVVFjNHdVNGRuTFBCOTQyQWdIa0o2U1ZWbFIyMmt6Z1VQU2MzU3JD?= =?utf-8?B?RlQ5UE5EWlI4YmVGNXNZck4vUW5MYnJMTkhCMEZsdENuTDVwWTEzbGZ6KzUz?= =?utf-8?B?MGlBdCtmc1N0dm5nUDREWFBiNnJpR1BHbVdqM2lEcHBjRGlZMEEwUUUxMHY0?= =?utf-8?B?aWZadU1HNjl2SDVUbmJyelVMclZ5bVR2bDlVS2JSU3pGUStOWllYMkZhNVl4?= =?utf-8?B?dmt3QXIwd0gxTE82MGpXWkRzN1o1LzJHSTJXYmxBRTJiek1aNHorSE1KVnhl?= =?utf-8?B?d0NIYWU4U3FmeU8xWVhtdGlGZWtYb1QwK1p6YllYa2NwNkQ0UUE4dHBlUEhP?= =?utf-8?B?QlNydXlJL2kyNjNid3Nsc1dRSXVWZG90U3R6Q3BrelpBQ1dTWndMSGt2amYy?= =?utf-8?B?QitpQVhqK0FtNkZ1RHlqa0xicHErUnlFNWN4dDJUWFNOOTRpTXR0anZKOXNi?= =?utf-8?B?aUh3S0RXMnBTeWcyNUdleGNXZ210ZVg5dENIUmZyZVBKS3lEWVQ2bWtneVY4?= =?utf-8?B?ZEYyM3oyK3hYYmZSSXNVTk1Kc2owUXNscThVajdzRitMSWRxdlM4Si9EVXIz?= =?utf-8?B?Z0F4RmZDMU53WDZYRnIxM0J4SjBOeDM0RDdqbkhnZm1wYWpVc1BNTTMvQVlC?= =?utf-8?B?NTJqbG94VnRvZmJEeVJ2RnptbjZITEVBTkF4aDFNVjRXU1N6T2h1VXYrb1Fr?= =?utf-8?B?N0MzNkR3ZVVQMzJtVmFiYVlkanFSMDlNWE4zM3FrOTFDSVc0eUN1SERUMXRo?= =?utf-8?B?b0RtL2NvMXV4T1FFN2tMdTZNTDEvb3ZzQ3BlMFZpTmdKNWJLZ2N1VHhjZXBN?= =?utf-8?B?ZHI2ZTM0VzI1NzJBdkppbjhveDRjTlVTUVYwc2pxMTI5dGkyb3NweURKdWdw?= =?utf-8?Q?TtpOtS38Tlve8I5Vx+17kEoAkJWEgCtZuWoiW3w?= X-OriginatorOrg: axentia.se X-MS-Exchange-CrossTenant-Network-Message-Id: 0d821ff7-040c-44ab-94c2-08d9086c8c69 X-MS-Exchange-CrossTenant-AuthSource: DB8PR02MB5482.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Apr 2021 04:34:15.6874 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4ee68585-03e1-4785-942a-df9c1871a234 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: CW7hIdGJuwQ4qlVIXBds3vo9/bBlmgrIDEdX5DIVPaQws8KSTS/8TD8vRiz5Ch/H X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB8PR02MB5849 Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On 2021-04-24 08:21, Kent Gibson wrote: > On Fri, Apr 23, 2021 at 05:32:15PM +0200, Peter Rosin wrote: >> Hi! >> >> I'm wondering if there is a way to request an output line using >> libgpiod without clobbering the previous value. I would like for >> an application to take a peek at this previous value of an output >> gpio and behave slightly different for 0/1. >> >> Cheers, >> Peter > > Assuming it is still an output then GPIOD_LINE_REQUEST_DIRECTION_AS_IS > should do what you are after. > But there is no guarantee that the line state is preserved across > requests, so YMMV. Excellent suggestion, I'll try that. And now I of course feel silly for not seeing it myself, it's so obvious... Thanks a bunch! Cheers, Peter