From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from AM0PR02CU008.outbound.protection.outlook.com (mail-westeuropeazon11023108.outbound.protection.outlook.com [52.101.72.108]) (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 1ACB33112C0 for ; Wed, 11 Mar 2026 05:23:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.72.108 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773206591; cv=fail; b=mEbKPxHGoIbT7P71SZ8/HQO9G+bxYrxBkCT42fC/LNX/0t1bXv0tuFluGQRGEQnOF0N1k6xC1V95dNYbokDLc5eq/zKMbWSwsntpkiUoPfG812gyTGu6kdp4cI4++MWxJNXDKnv6adi9Y+2ycNIrBUUByvas+duc+cpwukgHS/Y= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773206591; c=relaxed/simple; bh=ctFYGB7aE+R0eXHrTwL004YLDUOAw/F56dXPt70QtlM=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=VHbLT3Jv9DR+Zf6GbyrpXXNQ5fT1Vnix0sirvH5Gg4HD0T1Il9BLmI/54bHpRWFMjcOmb6GZwB46NfbSJojDMblEy6XAyhbNlx7eHqoX/Kc+7IahROUydmN51h6qI3ToQCmpIbVXXbc9ZN5Naf9hn9hKMcPSSc/ZDyruVNfX0bg= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=vaisala.com; spf=pass smtp.mailfrom=vaisala.com; dkim=pass (2048-bit key) header.d=vaisala.com header.i=@vaisala.com header.b=m37/5ZHG; arc=fail smtp.client-ip=52.101.72.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=vaisala.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=vaisala.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=vaisala.com header.i=@vaisala.com header.b="m37/5ZHG" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=GinRKUuIqTkAD0loB01Co3v6y/aiWDxZpXjtL4KFKlawBw5elZB4+4y9YXpDcB/9a0eqW/CuLIvZLBYkw/vse5e8s49lwRx8Z3FEtKxJU7hDnlzlJoTnTq6fdSnotwxVQaODdAqsf/CVMSe3q/3zJQuZWHtTK3VqnA+PltsEe5R5byuo0Wp4nQZ+WJOwVKXzqXK9X7ZPj0FoHTlePOZc55IzsAPv4gbyYtgbGViu5+C+OKYRInokoK4iT9wAFAKCnsBhHh/LhSmCwSLxFqqrgPlBELvLW5dsSQQCZ80ENXewsqePXc8XBUEds4XaUGfuMuWAJAgBLjEFltDrqmePNw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=b7CXCUc7slUoA/oN7sbJ7ngPeuKslo+CfriHl2QGrjg=; b=psqvm2FJmjI63HlQOstt1Bfn8hEXxei9w2QfSNrQSrlAnE7LYFrrKeDObQUpmteqEBT4e2NFUfA76oZWGVDvSRJDS9NTLQNHwMCNmACWcm0LUJukudsHb43Hm36tfxAJpG7n+O5I2zEr5cp9yB5wYwkGEb2l8ytLicUQUIfKnbJBKMaTf6w4UfOuO0iLluOZWgu/ivz1GECs32h+gkwJwrx5d4mLSBG+ZOIJtMON40jbh1aQNFO0AxCcN+CK3Q4VklgFDpg6uq5rO/lvWkv/Gh4QOlIiCToMRoDXdE8/R6z1NtK5fzUNSP6M0d+2/ALwP2zd4ufmCTMaZ3mP7Ppaug== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=vaisala.com; dmarc=pass action=none header.from=vaisala.com; dkim=pass header.d=vaisala.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=vaisala.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=b7CXCUc7slUoA/oN7sbJ7ngPeuKslo+CfriHl2QGrjg=; b=m37/5ZHGNgwjXQQJJ9XAESfejnuxg7KSUtMGFXho19Jk4NuCdE2zduIZ9qvBSRFsItyd+GjsuUW3HUwOP76ntEYmxxPPPP+ZWH068oGnK2vKDn9C+WXK5pxDkyUOYD3jj91U1mYbyJUSQWzdr0BgnYPaa6jwYXxxJmh/iwn1gR35u88DoUdfUGmiLRUgKBLIssonpm2bUGgUHRy7hNIvWfZzP8yLlxSnZGgK4X17RvLNHUB80wQTN1ajDhvAS0Iry5MlQbPKlzOQRWFze5ENMfHIu5oh42laV2gL5XVOdsmCO4MZzg9RgkhoeS9wTvIAWZ5yFJA71VR2rJdDOG5N9w== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=vaisala.com; Received: from VI0PR06MB10639.eurprd06.prod.outlook.com (2603:10a6:800:2f4::10) by PA2PR06MB9436.eurprd06.prod.outlook.com (2603:10a6:102:405::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9678.24; Wed, 11 Mar 2026 05:22:58 +0000 Received: from VI0PR06MB10639.eurprd06.prod.outlook.com ([fe80::3a41:90d:2091:bfee]) by VI0PR06MB10639.eurprd06.prod.outlook.com ([fe80::3a41:90d:2091:bfee%4]) with mapi id 15.20.9678.017; Wed, 11 Mar 2026 05:22:58 +0000 Message-ID: Date: Wed, 11 Mar 2026 07:22:56 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [QUESTION] rtc: zynqmp: CALIB_RD reset behavior differs between ZynqMP and Versal To: Takumi Ando , Alexandre Belloni , linux-rtc@vger.kernel.org Cc: michal.simek@amd.com, Yasushi SHOJI , kanta tamura References: <9ed6823e-b381-4de5-b1cf-98f5dc54bb7c@vaisala.com> <202603061113298cbba29d@mail.local> Content-Language: en-GB From: Tomas Melin In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: GVYP280CA0025.SWEP280.PROD.OUTLOOK.COM (2603:10a6:150:f9::20) To VI0PR06MB10639.eurprd06.prod.outlook.com (2603:10a6:800:2f4::10) Precedence: bulk X-Mailing-List: linux-rtc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VI0PR06MB10639:EE_|PA2PR06MB9436:EE_ X-MS-Office365-Filtering-Correlation-Id: 0c30fed5-ede5-4b94-b68d-08de7f2e41cf X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024|56012099003|22082099003|18002099003|7053199007; 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:VI0PR06MB10639.eurprd06.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(376014)(1800799024)(56012099003)(22082099003)(18002099003)(7053199007);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?VnpFSExmd3JaaVdHbUd5NlFWMExwUWtJYTUyYzRNWVZka1EwZS9KUW54MzRH?= =?utf-8?B?MzFyQzJOVkRoSXlIN2U2RGRYSEZuTTNQcGZEbjY1V3RzeXJqdGN1ZEpUMTZG?= =?utf-8?B?MWRTZ3hRLzlSNDlCS2ZOaUNEeFIxSXV4Mk5PK2haOGJEWW9idlhUajVFbXJn?= =?utf-8?B?OHpRSzJQMFBGYkw0K3liMjZCSEdQM01RMlRGWjBMd0lpTENSVTFFeTNUejBw?= =?utf-8?B?eEZlcEdySUZmVEdBbG1KT0hBQm1TM0M5MjAxSHV2eW0zbkF0NU1RaFh3L0Vi?= =?utf-8?B?WlRjb1lmTytiT2NzaGIzWHFqWi93QVZoZDhTSVJtQ0tBcnpaczJKMXRtazNx?= =?utf-8?B?dEFJamhQZkFpVnI2Uyt2Q1RDeHpNSnUyN0JFK1ZiWVZuNkp2bjNkTG5SK2hV?= =?utf-8?B?bzZ3MS9kQmFWb2xWd29aUm1FN1FDeGcwRitpQllRL3BVNlFabE00ay9FSkRC?= =?utf-8?B?MTV1emFpZVJVRzZNdlhCd3RYRE1hdWhhVkduZE9CYU13UjJQZTFhRWlSckdE?= =?utf-8?B?TWNIbXpGRnptT21UTzI3NmJQT3BEVDYzTjZaZHBlSXY5WllmV2FiRHVZc3Ny?= =?utf-8?B?RmVUeWplWnpVY0xBZmZZZ0dOdlA4Rm42Q0RHbC9xSEtCSnVmd2hwQXZaeElP?= =?utf-8?B?VUhZZ2xwditocEdBTm1zUTh4eEwxcHkyL2JzMTlBRDZkeXN5SHB6VVBMdVpM?= =?utf-8?B?S21nME5QZnZ0UE9IZlJLNHF0RGRtOXJJQVRHdWRrL0NIaDloYnJzUFpZb0ZU?= =?utf-8?B?KzFSZWNyeWRWM2hmbXpUalVSdlZBNVNwY3V1Rk9rSGdUbVlMVEtDalRySE1i?= =?utf-8?B?U3ZzZWRJVkV1enFkYkdickUxV2JjTUlvTjd1SFFRd2FSRDZ4L243bThzTG1E?= =?utf-8?B?UHhROXBWaS9XYnRFTk9PVTBwRWpvcktLZGdMaUZtYW5pQkwwR3E2dDZnRWpt?= =?utf-8?B?QzBCWlVHT3M4ZzNoeE4vZEJNWW5LOVBhNkVEbENhanVMMXJ6Tk5BT3haMDRB?= =?utf-8?B?NEhPbmwxT3gzN2VrQS9LOHBDZWh6OVYycEJLOG9PK3lyTXVHb0pmdUMyMTV0?= =?utf-8?B?eWVDVUltMWp5V09WODFGc1lPYzZSSHk2aHplYTZHb3k5VEFRR0EvS2V5ZlJx?= =?utf-8?B?NWRubXE2RkttS0NsS0lEWDRvRDNod0t0WmQ2dlpzbVN1RC9DU3NmNnJITDJq?= =?utf-8?B?aUxvbmZ6dmpic1Z0SjMyT3FVRTRhYWxLR0pZRnYwUUE0Z1ZHMDl6OXp5b244?= =?utf-8?B?K1NyaktoSDJXSEhjNnc2VDQ4VWRjMGtvTXd1RnF3elZPSVpodXgrZmN4ai9S?= =?utf-8?B?d2JwNHZBSFloV3czQWN1N29NeXA0aEtXWFJKRHZiT3VVZ3ZBY0lXRDRRWnJM?= =?utf-8?B?bks1U0I5ajQ5ajE0MDFxNjlkZzhTS2w4ZTQ5Und4NFRlODlRMzkvTGVkU0s5?= =?utf-8?B?ektidXVYbVN5bGlLUVVINUEwK094L1ZWbS9WOHVYUmwySi9RaHlhNkdTM3Qw?= =?utf-8?B?c2Fsb1dVTGNHazFNWUpoQW5kTXlGNE1ZRUFwR2sybkFMR25rRG41aUtSQkRO?= =?utf-8?B?MTltR21Ed3RBd2c0TTk3aGVFMW1JYWt5bkxlRmcwVVpYREdUMk9WMHp3U0tm?= =?utf-8?B?SEQ1TzFwdFlGckdkTVpsQkhvbm13ZHgwd1VjTWF0N3FDU050dlJVNjBHQ085?= =?utf-8?B?Z29lbk4vaGZlRnFVaklzWmVqVDhIOHRvb1J1V2FnbXQ1UGRWY3orRXRDTlVr?= =?utf-8?B?c3RoaGtUNnZHSkRKY24xcUpianlxTjFNTUExUWZvSURsOTV5cjdZdzkvV3V0?= =?utf-8?B?YSt1cWJVNkNDWS80VURGRnpiS0hOd2FHeGlkZnlJVE5VK1ZLTjJDVUwrVzIy?= =?utf-8?B?RW1OVVRHZmpGUkYveDFGTWFQekppemNZYkFSZVlkS3ltRWp5MHBZOGV5dXVF?= =?utf-8?B?MmxVNjRCRmt0U0ZVM0NTV2x3TVAyMVgzNDl5RTBhZjZ1YzlwVllrb2czWEdh?= =?utf-8?B?SmFOR2NRbFBVNkZDQTRUUHVRUXZRSGY2ZUw0OTVyVU9GNGdPa1duL1N6QWc1?= =?utf-8?B?UXllYmN1VkRDYVZYNXlWL1R2a3hseVk4WUVYQzNmM1d4RHh0Vm1odW9DY1BI?= =?utf-8?B?dGp5TjlaTTJaM2dXb2RsN3RJN3IxWWxxc1NuK2VMMWkvQVNFdDBOSVpibkVa?= =?utf-8?B?NWt1NWRtdGRtNHpobkN0UTFlSzBmWG5HR00zZVZMSmZ6L281YnZIcEZqNE1U?= =?utf-8?B?NVN4WStwS0QyUzNtR2tiZmZ3WHZibHdYQU1wMThEUW9GWnhJVHVQRHZSVm1h?= =?utf-8?B?YU4wc3BMTGpoVCtqNnlhN2t2cXdoK2g0MHZvMWU0WVJYN1VYZVkzenVFRk9k?= =?utf-8?Q?TTkgJ/iD4XW5qFIU=3D?= X-OriginatorOrg: vaisala.com X-MS-Exchange-CrossTenant-Network-Message-Id: 0c30fed5-ede5-4b94-b68d-08de7f2e41cf X-MS-Exchange-CrossTenant-AuthSource: VI0PR06MB10639.eurprd06.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Mar 2026 05:22:58.3641 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 6d7393e0-41f5-4c2e-9b12-4c2be5da5c57 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: DEzmafe4hrQQl+VXvgbWPfC0f0J33ms8Bz1xlx0QkUl7Ykt1mx8oyLR3TRd2Oy1lgARSo8ruwYO9KYrj5GQQHg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PA2PR06MB9436 Hi, On 11/03/2026 05:19, Takumi Ando wrote: > [You don't often get email from takumi@spacecubics.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] > > Hi Tomas, Alexandre, > > Thank you for the explanations. > > So if I understand correctly, both on Zynq UltraScale+ and Versal, > CALIB_RD may return a non-zero (or otherwise undefined) value after > reset, meaning that it cannot reliably be used to determine whether > the calibration register has already been initialized. > > While the fractional calibration should indeed be handled from > userspace (e.g. via the RTC offset interface), it seems that the > Max_Tick field should still always be programmed according to the > value provided in Device Tree, since it depends only on the RTC > oscillator frequency. Both max_tick and fract_data might change, it depends on how big the calibrator drift/offset is and if it is negative/positive. > > Would it make sense for the driver to always program Max_Tick from the > Device Tree "calibration" property while preserving the fractional > calibration bits currently stored in hardware? As Alexandre mentioned, user space needs to ensure calibration is what it should be. thanks, Tomas > > If this approach sounds reasonable, I would like to prepare a patch > for upstream. > > Best regards, > > 2026年3月6日(金) 20:13 Alexandre Belloni : >> On 06/03/2026 12:09:40+0200, Tomas Melin wrote: >>>> On Zynq UltraScale+ Devices Register Reference (UG1087) [2], >>>> CALIB_RD resets to 0, so the current logic works correctly there. >>>> However, this assumption does not appear to hold for Versal. >>> For Ultrascale+ the calibration register also gives random values after >>> reset, perhaps you have noticed this: >>> https://adaptivesupport.amd.com/s/article/000036886?language=en_US. Maybe >>> the same can occur also on Versal. >>> >>> AFAIK there is no way of knowing if the value is correct or not after reset, >>> so user space helpers might be needed to maintain the calibration value at a >>> desired value. >>> >> Userspace is always needed to put the proper calibration, there is no >> way for the kernel to know what value to put there. In the support case >> above, the crystal will never be exactly 32768Hz and this value will >> change over time and also depends on the temperature. The value always >> needs to be computed, if your device can do NTP, chrony will provide the >> proper offsets. If you don't have a way to measure the deviation, then >> userspace can always forcefully set /sys/class/rtc/rtcX/offset if it >> doesn't hold the correct value. >> There is no need for devmem here. >> >> -- >> Alexandre Belloni, co-owner and COO, Bootlin >> Embedded Linux and Kernel engineering >> https://bootlin.com/ > > > -- > Takumi Ando > Space Cubics Inc.