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Tue, 10 Sep 2019 02:47:59 +0000 Received: from DB3PR0402MB3916.eurprd04.prod.outlook.com ([fe80::8958:299c:bc54:2a38]) by DB3PR0402MB3916.eurprd04.prod.outlook.com ([fe80::8958:299c:bc54:2a38%7]) with mapi id 15.20.2241.018; Tue, 10 Sep 2019 02:47:59 +0000 From: Anson Huang To: Dong Aisheng , Stephen Boyd , Peng Fan Subject: RE: [PATCH] clk: imx: lpcg: write twice when writing lpcg regs Thread-Topic: [PATCH] clk: imx: lpcg: write twice when writing lpcg regs Thread-Index: AQHVXK/qRNohGClvt0yC94cqOwkPUKce9XOAgARa7gCAAPmTYA== Date: Tue, 10 Sep 2019 02:47:59 +0000 Message-ID: References: <1566936978-28519-1-git-send-email-peng.fan@nxp.com> <20190906172044.B99FB20838@mail.kernel.org> In-Reply-To: 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=anson.huang@nxp.com; x-originating-ip: [119.31.174.66] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 40c0b3e7-865a-4a8b-2aee-08d735994ae8 x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: BCL:0; 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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 Sat, Sep 7, 2019 at 9:47 PM Stephen Boyd wrote: > > > > Quoting Peng Fan (2019-08-27 01:17:50) > > > From: Peng Fan > > > > > > There is hardware issue that: > > > The output clock the LPCG cell will not turn back on as expected, > > > even though a read of the IPG registers in the LPCG indicates that > > > the clock should be enabled. > > > > > > The software workaround is to write twice to enable the LPCG clock > > > output. > > > > > > Signed-off-by: Peng Fan > > > > Does this need a Fixes tag? > > Not sure as it's not code logic issue but a hardware bug. > And 4.19 LTS still have not this driver support. Looks like there is an errata for this issue, and Ranjani just sent a patch for review internally, Back-to-back LPCG writes can be ignored by the LPCG register due to a HW bug. The writes need to be separated by atleast 4 cycles of the gated clock. The workaround is implemented as follows: 1. For clocks running greater than 50MHz no delay is required as the delay in accessing the LPCG register is sufficient. 2. For clocks running greater than 23MHz, a read followed by the write will provide the sufficient delay. 3. For clocks running below 23MHz, LPCG is not used. Need double check? Anson. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel