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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 F3148C43331 for ; Thu, 7 Nov 2019 19:19:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5B9B21882 for ; Thu, 7 Nov 2019 19:19:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573154374; bh=KfubhkiePCi8VGkvdxTatX01GSD+R9bZnDBflQTG4CI=; h=In-Reply-To:References:From:To:Cc:Subject:Date:List-ID:From; b=thu2k+h2odiyLXxgPdNBgIgyTtgcLVGpZjcA8Mnq8xawlKXRGmltb+iTFdZICyyMt ZHCBQEkOeiqUzXTHtyry1FfnZliR5GyX0GuoFTH3ux/DLudZm8jx+GYM7zHQeX1jzj gmoIlrvfXE1sYjJmIQIRqHp7o3vE2ivQv0diZ6Vg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725941AbfKGTTe (ORCPT ); Thu, 7 Nov 2019 14:19:34 -0500 Received: from mail.kernel.org ([198.145.29.99]:56370 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725851AbfKGTTe (ORCPT ); Thu, 7 Nov 2019 14:19:34 -0500 Received: from kernel.org (unknown [104.132.0.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0B18021D6C; Thu, 7 Nov 2019 19:19:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573154373; bh=KfubhkiePCi8VGkvdxTatX01GSD+R9bZnDBflQTG4CI=; h=In-Reply-To:References:From:To:Cc:Subject:Date:From; b=RJKgKFVCaeBna9mLw4V8SIefSFJ9vq3dizcCsSfD+RQg0zZnVwYAMsfFiPalN3xTI c3909sJB3vzB95Ew2++B34G5jx/fw9Jiwwehy2+u/MSzo2Zdm9XArrwlFaWu0qnXnN FOQvxYrC2Dl7kO5nQIEbXNtepqcwvm4DJKjYHCRA= Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable In-Reply-To: <20191107152115.GA2580600@ulmo> References: <1565984527-5272-1-git-send-email-skomatineni@nvidia.com> <1565984527-5272-8-git-send-email-skomatineni@nvidia.com> <20191106231005.F2CD820869@mail.kernel.org> <20191107152115.GA2580600@ulmo> From: Stephen Boyd To: Dmitry Osipenko , Thierry Reding Cc: Sowjanya Komatineni , jason@lakedaemon.net, jonathanh@nvidia.com, linus.walleij@linaro.org, marc.zyngier@arm.com, mark.rutland@arm.com, stefan@agner.ch, tglx@linutronix.de, pdeschrijver@nvidia.com, pgaikwad@nvidia.com, linux-clk@vger.kernel.org, linux-gpio@vger.kernel.org, jckuo@nvidia.com, josephl@nvidia.com, talho@nvidia.com, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, mperttunen@nvidia.com, spatra@nvidia.com, robh+dt@kernel.org, devicetree@vger.kernel.org, rjw@rjwysocki.net, viresh.kumar@linaro.org, linux-pm@vger.kernel.org Subject: Re: [PATCH v9 07/22] clk: Add API to get index of the clock parent User-Agent: alot/0.8.1 Date: Thu, 07 Nov 2019 11:19:32 -0800 Message-Id: <20191107191933.0B18021D6C@mail.kernel.org> Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org Quoting Thierry Reding (2019-11-07 07:21:15) > On Thu, Nov 07, 2019 at 03:54:03AM +0300, Dmitry Osipenko wrote: > > 07.11.2019 02:10, Stephen Boyd =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > > Quoting Sowjanya Komatineni (2019-08-16 12:41:52) > > >> This patch adds an API clk_hw_get_parent_index to get index of the > > >> clock parent to use during the clock restore operations on system > > >> resume. > > > =20 > > > Is there a reason we can't save the clk hw index at suspend time by > > > reading the hardware to understand the current parent? The parent ind= ex > > > typically doesn't matter unless we're trying to communicate something > > > from the framework to the provider driver. Put another way, I would > > > think the provider driver can figure out the index itself without hav= ing > > > to go through the framework to do so. > >=20 > > Isn't it a bit wasteful to duplicate information about the parent within > > a provider if framework already has that info? The whole point of this > > new API is to allow providers to avoid that unnecessary duplication. > >=20 > > Please note that clk_hw_get_parent_index is getting used only at the > > resume time and not at suspend. >=20 > I agree with this. All of the information that we need is already cached > in the framework. Doing this in the driver would mean essentially adding > a "saved parent" field along with code to read the value at suspend time > to the three types of clocks that currently use this core helper. Don't we already have a "saved parent" field by storing the pointer to the clk_hw? >=20 > That's certainly something that we *can* do, but it doesn't sound like a > better option than simply querying the framework for the value that we > need. >=20 Let me say this another way. Why does this driver want to know the index that the framework uses for some clk_hw pointer? Perhaps it happens to align with the same value that hardware uses, but I still don't understand why the driver wants to know what the framework has decided is the index for some clk_hw pointer. Or is this something like "give me the index for the parent that the framework thinks I currently have but in reality don't have anymore because the register contents were wiped and we need to reparent it"? A generic API to get any index for this question is overkill and we should consider adding some sort of API like clk_hw_get_current_parent_index(), or a framework flag that tells the framework this parent is incorrect and we need to call the .set_parent() op again to reconfigure it.