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 D68A0C4360C for ; Fri, 27 Sep 2019 12:41:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ACD3B20673 for ; Fri, 27 Sep 2019 12:41:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569588070; bh=OgMeke5Fk6Ke9Are++U1NlBfvseYb7B7HVu1BwnX0Ss=; h=To:Subject:Date:From:Cc:In-Reply-To:References:List-ID:From; b=Spj5pczTE3K/sv0WH0iggj260ozO+E3WgxyKvMhAYWy/i1yNEB4QfS4t5htYRzgmS XrjWIS+f/ATtKCImij7EUkhDl4C7UgvwamqEXyxfT29UjB2bvwiNYxA09Qla4GcY8X Q0FwcICi2YxvwdsLYUS30MlLI/7EvtCXdrWFQvZA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727512AbfI0MlK (ORCPT ); Fri, 27 Sep 2019 08:41:10 -0400 Received: from inca-roads.misterjones.org ([213.251.177.50]:42904 "EHLO inca-roads.misterjones.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726441AbfI0MlJ (ORCPT ); Fri, 27 Sep 2019 08:41:09 -0400 Received: from www-data by cheepnis.misterjones.org with local (Exim 4.80) (envelope-from ) id 1iDpYV-00084m-MZ; Fri, 27 Sep 2019 14:41:03 +0200 To: Benjamin GAIGNARD Subject: Re: [PATCH] ARM: dts: stm32: Enable high resolution timer X-PHP-Originating-Script: 0:main.inc MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Date: Fri, 27 Sep 2019 13:41:03 +0100 From: Marc Zyngier Cc: Alexandre TORGUE , , , , , , In-Reply-To: <341949c8-7864-5d65-2797-988022724a4c@st.com> References: <20190927084819.645-1-benjamin.gaignard@st.com> <341949c8-7864-5d65-2797-988022724a4c@st.com> Message-ID: X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/0.7.2 X-SA-Exim-Connect-IP: X-SA-Exim-Rcpt-To: benjamin.gaignard@st.com, alexandre.torgue@st.com, robh+dt@kernel.org, mark.rutland@arm.com, devicetree@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-09-27 13:36, Benjamin GAIGNARD wrote: > On 9/27/19 1:22 PM, Marc Zyngier wrote: >> On 2019-09-27 09:48, Benjamin Gaignard wrote: >>> Adding always-on makes arm arch_timer claim to be an high >>> resolution >>> timer. >>> That is possible because power mode won't stop clocking the timer. >> >> The "always-on" is not about the clock. It is about the comparator. >> The clock itself is *guaranteed* to always tick. If it didn't, >> that'd be >> an integration bug, and a pretty bad one. >> >> What you're claiming here is that your CPU never enters a low-power >> mode? >> Ever? I find this very hard to believe. >> >> Furthermore, claiming that always-on is the way to force the >> arch-timer >> to be an hrtimer is factually wrong. This is what happens *if* this >> is >> the only timer in the system. The only case this is true is for >> virtual >> machines. Anything else has a global timer somewhere that will allow >> the arch timers to be used as an hrtimer. >> >> I'm pretty sure you too have a global timer somewhere in your >> system. >> Enable it, and enjoy hrtimers without having to lie about the >> properties >> of your system! ;-) > > Hi Marc, > > This SoC doesn't have any other global timer. Use arch_time is the > only > we have to provide hrtimer on this system. And you don't have any form of power management either? What happens when your CPU goes into idle? If your system does any form of power management *and* doesn't have a separate timer, it is remarkably broken. M. -- Jazz is not dead. It just smells funny...