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x-microsoft-antispam-message-info: MRYl+TyJCFLYEz6gHzgIhZCWTZbAbv1ngsrwzpntyq9QgZkl7vQK+2lBksr/0xn+qOkJOC9Wj5pi5kjn+3MrrGZj3rtOvPun4brCSS/UmlZEf4u3Ba+eV4WiL/gt5o/iaOqZoBigTlhJcI6/E4AYGokzkhefb2MQ9jBpACBxYlgZURMgHY6j2KSliJEhvdfOqW+N4vB6enpSbIBnmNq+9TJMIiFlnrrwCUc0DIa8jzLd68NWqZrMIw8ywd3JWgc5H+JTMIluJnW4XzHBMUM3zg1eLqBJUkTgms8r/jVpQNxviLskzX7irHiwoxC39vV9Xvz7ggyp/IxB92KGDRE7hyVGt4D077TsSd7rMJUNYSsziMXZev9rO2O/Bp81St4DW+GGE2JQ+Ybc2VfNbC/mo5RV4pGbkWroMu1P35MGIOAO0oOFLK23YQ0PIcO4J9S7 x-ms-exchange-antispam-messagedata: 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nxp.com X-MS-Exchange-CrossTenant-Network-Message-Id: 1ad6f389-9b18-4beb-3a3f-08d7eae2082b X-MS-Exchange-CrossTenant-originalarrivaltime: 27 Apr 2020 19:34:41.4862 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: l9TX6lmYzP/+JWZwwslIA0IsPjEtnK3LWUVLyrbSHdEbmIWEO4wHMHrgYdy+nOGD6nabxRpenvc8lxJkNMPBGQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR04MB4238 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-04-27 12:15 PM, Peng Fan wrote:=0A= >> Subject: Re: [PATCH V2 07/10] clk: imx: add mux ops for i.MX8M composite= =0A= >> clk=0A= >>=0A= >> On 2020-03-12 12:27 PM, Peng Fan wrote:=0A= >>> From: Peng Fan =0A= >>>=0A= >>> The CORE/BUS root slice has following design, simplied graph:=0A= >>> The difference is core not have pre_div block.=0A= >>> A composite core/bus clk has 8 inputs for mux to select, saying clk[0-7= ].=0A= >>>=0A= >>> SEL_A GA=0A= >>> +--+ +-+=0A= >>> | +->+ +------+=0A= >>> CLK[0-7]--->+ | +-+ |=0A= >>> | | | +----v---+ +----+=0A= >>> | +--+ |pre_diva+----> | +---------+=0A= >>> | +--------+ |mux +--+post_div |=0A= >>> | +--+ |pre_divb+--->+ | +---------+=0A= >>> | | | +----^---+ +----+=0A= >>> +--->+ | +-+ |=0A= >>> | +->+ +------+=0A= >>> +--+ +-+=0A= >>> SEL_B GB=0A= >>>=0A= >>> There will be system hang, when doing the following steps:=0A= >>> 1. switch mux from clk0 to clk1=0A= >>> 2. gate off clk0=0A= >>> 3. swtich from clk1 to clk2, or gate off clk1=0A= >>>=0A= >>> Step 3 triggers system hang.=0A= >>>=0A= >>> If we skip step2, keep clk0 on, step 3 will not trigger system hang.=0A= >>> However we have CLK_OPS_PARENT_ENABLE flag, which will unprepare=0A= >>> disable the clk0 which will not be used.=0A= >>=0A= >> As far as I understand when switching from clk1 to clk2 this is done by= =0A= >> temporarily switching the rightmost SELECT mux to whatever was in the=0A= >> spare SEL, which is essentially arbitrary from linux POV.=0A= > =0A= > No. The fixes in this patches has been confirmed by IC design owner=0A= > =0A= >>=0A= >> This is quite unexpected but in theory it might be desirable to use a th= ird=0A= >> parent as a fallback.=0A= > =0A= > No. this will make things complicated. To CCM SEL_A and SEL_B,=0A= > it is controlled by a hardware counter. Saying you write n times to=0A= > the target interface.=0A= > =0A= > The mux will use n % 2 to choose SEL_A or SEL_B. write twice=0A= > to make sure SEL_A and SEL_B has the same value.=0A= =0A= What if SEL_A and SEL_B have different values on boot? The first time =0A= linux does set_parent it will switch to the other SEL_X which might be off.= =0A= 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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 288F9C4CECD for ; Mon, 27 Apr 2020 19:34:57 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 012922078C for ; Mon, 27 Apr 2020 19:34:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="IIjv0gRc"; 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Mon, 27 Apr 2020 19:34:41 +0000 Received: from VI1PR04MB6941.eurprd04.prod.outlook.com ([fe80::8de5:8c61:6e4d:9fe9]) by VI1PR04MB6941.eurprd04.prod.outlook.com ([fe80::8de5:8c61:6e4d:9fe9%9]) with mapi id 15.20.2937.020; Mon, 27 Apr 2020 19:34:41 +0000 From: Leonard Crestez To: Peng Fan , Anson Huang Subject: Re: [PATCH V2 07/10] clk: imx: add mux ops for i.MX8M composite clk Thread-Topic: [PATCH V2 07/10] clk: imx: add mux ops for i.MX8M composite clk Thread-Index: AQHV+FjQMBLZK1sUBkmPtGWbyCJKZA== Date: Mon, 27 Apr 2020 19:34:41 +0000 Message-ID: References: <1584008384-11578-1-git-send-email-peng.fan@nxp.com> <1584008384-11578-8-git-send-email-peng.fan@nxp.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: spf=none (sender IP is ) smtp.mailfrom=leonard.crestez@nxp.com; x-originating-ip: [95.76.3.222] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 1ad6f389-9b18-4beb-3a3f-08d7eae2082b x-ms-traffictypediagnostic: VI1PR04MB4238:|VI1PR04MB4238: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-04-27 12:15 PM, Peng Fan wrote: >> Subject: Re: [PATCH V2 07/10] clk: imx: add mux ops for i.MX8M composite >> clk >> >> On 2020-03-12 12:27 PM, Peng Fan wrote: >>> From: Peng Fan >>> >>> The CORE/BUS root slice has following design, simplied graph: >>> The difference is core not have pre_div block. >>> A composite core/bus clk has 8 inputs for mux to select, saying clk[0-7]. >>> >>> SEL_A GA >>> +--+ +-+ >>> | +->+ +------+ >>> CLK[0-7]--->+ | +-+ | >>> | | | +----v---+ +----+ >>> | +--+ |pre_diva+----> | +---------+ >>> | +--------+ |mux +--+post_div | >>> | +--+ |pre_divb+--->+ | +---------+ >>> | | | +----^---+ +----+ >>> +--->+ | +-+ | >>> | +->+ +------+ >>> +--+ +-+ >>> SEL_B GB >>> >>> There will be system hang, when doing the following steps: >>> 1. switch mux from clk0 to clk1 >>> 2. gate off clk0 >>> 3. swtich from clk1 to clk2, or gate off clk1 >>> >>> Step 3 triggers system hang. >>> >>> If we skip step2, keep clk0 on, step 3 will not trigger system hang. >>> However we have CLK_OPS_PARENT_ENABLE flag, which will unprepare >>> disable the clk0 which will not be used. >> >> As far as I understand when switching from clk1 to clk2 this is done by >> temporarily switching the rightmost SELECT mux to whatever was in the >> spare SEL, which is essentially arbitrary from linux POV. > > No. The fixes in this patches has been confirmed by IC design owner > >> >> This is quite unexpected but in theory it might be desirable to use a third >> parent as a fallback. > > No. this will make things complicated. To CCM SEL_A and SEL_B, > it is controlled by a hardware counter. Saying you write n times to > the target interface. > > The mux will use n % 2 to choose SEL_A or SEL_B. write twice > to make sure SEL_A and SEL_B has the same value. What if SEL_A and SEL_B have different values on boot? The first time linux does set_parent it will switch to the other SEL_X which might be off. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel