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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 838C8C7618B for ; Sun, 28 Jul 2019 11:38:38 +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 4D4FF2075B for ; Sun, 28 Jul 2019 11:38:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="VWdxRl0C" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4D4FF2075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Subject:To:From:Message-ID:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=nZOg2PDstjPnTXEjqFFnKRi0Tz461CkJZrbxNefRxT8=; b=VWdxRl0CG7G/K4 xJ4ZyZBFl6nUGzbtmo3Z25N4EVEgol6McMcIf8hDBRvXqOcCXKIWNCuxIJ7rTWcNqUPs6wqtq87CU VaJ2DRV8tvoF+lMedkfD5NKOXoEMSvb8XpFBgbbHY/7Rb7cfT8xZQHbsxn9viC/m4GU67DjVSsYIP VwFdE4EmAhyC0MGrhEr/chBoAlnJrJjEh25gtLO+o0Ag2n/IRJr0+iGBKfqljHSOq+Q1aRg/AfC5U gBAmyJBBRhRxKHdcXxesJ3RznEgqc3igGjZJLKrlU7y4LGOpMVarWKmq1U9wiBv3/l3ro6ukgSrYH sYXpWZ0N+t43NL4042xQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hrhVd-0001ZY-Fr; Sun, 28 Jul 2019 11:38:37 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hrhVa-0001Z8-Pj; Sun, 28 Jul 2019 11:38:36 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C94A5337; Sun, 28 Jul 2019 04:38:31 -0700 (PDT) Received: from big-swifty.misterjones.org (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AB7A63F71F; Sun, 28 Jul 2019 04:38:27 -0700 (PDT) Date: Sun, 28 Jul 2019 12:38:26 +0100 Message-ID: <86v9vmmlsd.wl-marc.zyngier@arm.com> From: Marc Zyngier To: Stefan Wahren Subject: Re: [PATCH RFC 18/18] ARM: dts: Add minimal Raspberry Pi 4 support In-Reply-To: References: <1563398164-2679-1-git-send-email-wahrenst@gmx.net> <1563398164-2679-5-git-send-email-wahrenst@gmx.net> <20190723191326.3afdff83@why> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 EasyPG/1.0.0 Emacs/26 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Organization: ARM Ltd MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190728_043834_925369_F40348E7 X-CRM114-Status: GOOD ( 25.60 ) 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 , Ulf Hansson , Florian Fainelli , Scott Branden , Stephen Boyd , Ray Jui , Linus Walleij , Mark Brown , Adrian Hunter , Eric Anholt , Rob Herring , bcm-kernel-feedback-list@broadcom.com, Stefan Wahren , Nicolas Saenz Julienne , Michael Turquette , linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org Content-Type: text/plain; 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 Hi Stephan, On Sun, 28 Jul 2019 11:58:58 +0100, Stefan Wahren wrote: > > Hi Marc, > > Am 23.07.19 um 20:13 schrieb Marc Zyngier: > > On Wed, 17 Jul 2019 23:16:04 +0200 > > Stefan Wahren wrote: > > > >> This adds minimal support for the new Raspberry Pi 4 without the > >> fancy stuff like GENET, PCIe, XHCI, 40 bit DMA and V3D. The RPi 4 is available > >> in 3 different variants (1, 2 and 4 GB RAM), so leave the memory size to zero > >> and let the bootloader take care of it. > >> > >> Other differences to the Raspberry Pi 3: > >> - additional GIC 400 Interrupt controller > >> - new thermal IP and HWRNG > >> - additional MMC interface (emmc2) > >> - additional UART, I2C, SPI and PWM interfaces > >> > >> Signed-off-by: Stefan Wahren > >> > >> ... > >> + }; > >> + > >> + timer { > >> + compatible = "arm,armv7-timer"; BTW, this should be "arm,armv8-timer". > >> + interrupts = >> + IRQ_TYPE_LEVEL_LOW)>, > >> + >> + IRQ_TYPE_LEVEL_LOW)>, > >> + >> + IRQ_TYPE_LEVEL_LOW)>, > >> + >> + IRQ_TYPE_LEVEL_LOW)>; > >> + arm,cpu-registers-not-fw-configured; > > Really? :-( > i asked about that [1] and they said that the arm stubs [2] only set the > timer frequency and zeroing CNTVOFF_EL2. Who is "they"? As long as it is done on all CPUs, that's the right thing to do, and this property is pretty useless in that case. > > > >> + always-on; > > I'm pretty sure that's not the case. This indicates that you can power > > the CPU off, bring it back on, and yet have your timer alive and > > kicking. The only case this actually exists is for VMs. I can see it > > being cargo-culted from previous RPi revisions, but that doesn't make > > it true. > > They said that they used this to suppress high interrupt load for the > timers. Indeed, and that's the only thing the kernel can do if it isn't provided with a global timer that can be used as a backup then the CPUs transition to a deep idle state where the timers are not actually running. If you have such a global timer, enable it and you'll see the interrupt rate dropping like a rock. Don't you have a brcm,bcm2835-system-timer stashed somewhere? If you don't have such a timer, then the question is whether the CPUs can go into a deep enough sleep state where the timer comparator is disabled, leading to missed events. If this system can only reach very shallow sleep states, then always-on is OK. Otherwise, this is a total lie and you're likely to miss timer events. Thanks, 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