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=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 EBD48C4360C for ; Fri, 27 Sep 2019 12:41:16 +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 C005320863 for ; Fri, 27 Sep 2019 12:41:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="WY9fYqDA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C005320863 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-ID:References:In-Reply-To:From:Date: MIME-Version:Subject:To:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=F/rnLdZo8dG//wcHT0u70DEhX/VdGMy+XEWVj30RXYo=; b=WY9fYqDAexGOMH/0ifHHDjYft Cgh7gG+sQxl0j77WtbU37hy0n/o6vBI9Crd2MJXMuuvQU+12AYpgXOkSK6TKlpzyvL8Dfs0AsZR2w rWcYxgRBV7IZIA0BwSzkPZwxKJAKfe3BMnASZL2hMDdQc1zH3iS8ha5bKTia4QW+ndGei636wt71D v6jAYSBV6i6id3Znxho2VfVBz8Y5YLD2/tXlEMRB8ET3v8kPTIYfDmeqJ7d8Vy9jpQjauNfj2+kfv u/DhVL0BLzVDvtqTDPYIuJGo6rReCWX3X3P0lXb+iRBNmkdeFYtf1c5msyvEpOykkjaRSEdC5zepc eQvdXzZ8w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iDpYi-0006rL-Cj; Fri, 27 Sep 2019 12:41:16 +0000 Received: from inca-roads.misterjones.org ([213.251.177.50]) by bombadil.infradead.org with esmtps (Exim 4.92.2 #3 (Red Hat Linux)) id 1iDpYa-0006qP-Vi for linux-arm-kernel@lists.infradead.org; Fri, 27 Sep 2019 12:41:15 +0000 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 Date: Fri, 27 Sep 2019 13:41:03 +0100 From: Marc Zyngier 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190927_054114_025786_AC6159FC X-CRM114-Status: GOOD ( 11.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, devicetree@vger.kernel.org, Alexandre TORGUE , linux-kernel@vger.kernel.org, robh+dt@kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel