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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 7C6CDC43387 for ; Wed, 16 Jan 2019 14:10:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 541A120859 for ; Wed, 16 Jan 2019 14:10:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391147AbfAPOKb (ORCPT ); Wed, 16 Jan 2019 09:10:31 -0500 Received: from mx07-00178001.pphosted.com ([62.209.51.94]:2846 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390689AbfAPOKb (ORCPT ); Wed, 16 Jan 2019 09:10:31 -0500 Received: from pps.filterd (m0046037.ppops.net [127.0.0.1]) by mx07-00178001.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x0GE6W1r002001; Wed, 16 Jan 2019 15:10:11 +0100 Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx07-00178001.pphosted.com with ESMTP id 2pybywmaaq-1 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT); Wed, 16 Jan 2019 15:10:11 +0100 Received: from zeta.dmz-eu.st.com (zeta.dmz-eu.st.com [164.129.230.9]) by beta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 72AE634; Wed, 16 Jan 2019 14:10:10 +0000 (GMT) Received: from Webmail-eu.st.com (sfhdag5node3.st.com [10.75.127.15]) by zeta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 028092D41; Wed, 16 Jan 2019 14:10:10 +0000 (GMT) Received: from [10.48.0.167] (10.75.127.45) by SFHDAG5NODE3.st.com (10.75.127.15) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 16 Jan 2019 15:10:09 +0100 Subject: Re: [PATCH v2 2/3] mfd: syscon: Add optional clock support To: Arnd Bergmann CC: Lee Jones , Rob Herring , Alexandre Torgue , Maxime Coquelin , Mark Rutland , Gabriel Fernandez , DTML , Linux Kernel Mailing List , , Linux ARM References: <1544604495-4082-1-git-send-email-fabrice.gasnier@st.com> <1544604495-4082-3-git-send-email-fabrice.gasnier@st.com> From: Fabrice Gasnier Message-ID: <9e0ee154-a399-9bff-3beb-adfd9d6c6fee@st.com> Date: Wed, 16 Jan 2019 15:10:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.75.127.45] X-ClientProxiedBy: SFHDAG7NODE3.st.com (10.75.127.21) To SFHDAG5NODE3.st.com (10.75.127.15) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-16_05:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/16/19 1:14 PM, Arnd Bergmann wrote: > (sorry for the late reply, I just realized that I had never sent out the > mail after Lee asked me for a review last year and I had drafted > my reply). Hi Arnd, Many thanks for reviewing, no worries :-) > > On Wed, Dec 12, 2018 at 9:48 AM Fabrice Gasnier wrote: >> >> Some system control registers need to be clocked, so the registers can >> be accessed. Add an optional clock and attach it to regmap. >> >> Signed-off-by: Fabrice Gasnier > > This looks ok to me in principle, but I have one question: When we > do a clk_get() and clk_prepare() as part of regmap_mmio_attach_clk(), > does that change the behavior of syscon nodes that are otherwise > unused? I'm not sure I correctly understand this question. I don't think it will change the behavior for "unused" nodes. These should remain unused with this patch. > > I think we have a bunch of devices that started out as a syscon but > then we added a proper driver for them, which would handle the > clocks explicitly. Is it guaranteed that this will keep working (including > shutting down the clocks when they are unused) if we have two drivers > that call clk_get() on the same device node? I'd expect nothing wrong happens when two drivers call clk_get() for the same clock. Are there some case where two drivers are bind (e.g. syscon driver + another driver) for the same piece of hardware ? The clk_prepare() is part of regmap_mmio_attach_clk(). It's called once upon registration via of_syscon_register(). There is currently no mean to unregister, e.g. something like "of_syscon_unregister" and so do clk_unprepare via regmap_mmio_detach_clk(). Then point is clk_enable()/clk_disable() calls will be used in regmap_mmio_read() and regmap_mmio_write(). These calls are balanced. Then clock framework should correctly disable/gate the clock when unused, based on the enable count. Is this answering your question? Thanks again, Best regards, Fabrice > > Arnd >