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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 1F37AC531C9 for ; Sun, 26 Jul 2026 12:42:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: References:In-Reply-To:Subject:Cc:To:From:Message-ID:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=5biH2onDtuL3obuel5O14yJjmvxIh8PysG2Ka/dgiUM=; b=Z80aUYp/t/iK89jlAoAuCHwfEj S09hTsa+NK3OXen98/hXq+g/kMl+xq6P4w7VtKmQg7hNvZMA3aVemo2sbj6WhI2rB5N6TqBcGirRa GFqmmWV8J7YcbLk/LwiKJkBkb+0mtndwdPsQMDSQ2zHsdfdSKg31o6/cFqVHyvhPi8qQuWnG4yTKy 15n70027/4qpA4moXMy59eF22Udi3KvhhiPBYLd+uLZPJt7RlgrzhvH9350tiM0Wex8jXQmal+q+7 7H/qOm/7Z7+G2pPPw7HBt9o/RD2yVQUTQIIwC2mH1jRaRa2ZSfoleacSqsMlOeXW/skhlQUhVJpky 11yWo4pw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wnyB2-00000001AdX-0krD; Sun, 26 Jul 2026 12:41:56 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wnyB1-00000001AdM-2utE for linux-arm-kernel@lists.infradead.org; Sun, 26 Jul 2026 12:41:55 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id E018460008; Sun, 26 Jul 2026 12:41:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8CC331F000E9; Sun, 26 Jul 2026 12:41:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785069712; bh=5biH2onDtuL3obuel5O14yJjmvxIh8PysG2Ka/dgiUM=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=b0OjmfyOWSB9qYRdhDb/4BdQ0Bj0xrTw1itUIGwyUj26THtEejRytD9zHoj7sOocr S/M64/3J/39aWkSM9yaynUp5DQOxle9Fq0D3Zx40+TjZAPE8nFMEKbYWJ58IngK6XQ NovOrRXNtKknsIXkgGzgFkQ5ok/nBQ7XccUKVFJoespLn8quX5fFGOtecYhNw1Z725 moPTL7HhxmZmOli4uU+ucWlNFlduyG14w1kzxaHqwEqgmHIn8wGCkILewU4t6OAoB8 wPAaVIebQJeyefsmpC5iJ1PmyXZno8H6b0BuG/8ILCIRcrYNcIMIHDPcByPMlqr59Q egfWS21TMfyqQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=lobster-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wnyAw-00000008wye-1d4a; Sun, 26 Jul 2026 12:41:50 +0000 Date: Sun, 26 Jul 2026 13:43:14 +0100 Message-ID: <87tsplq5ul.wl-maz@kernel.org> From: Marc Zyngier To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Catalin Marinas , Mark Rutland , Thomas Gleixner , Ben Horgan , Daniel Lezcano Subject: Re: [PATCH v2 0/5] arm64: arch_timer: Improve errata handling In-Reply-To: References: <20260508094203.2913880-1-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: will@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, tglx@kernel.org, ben.horgan@arm.com, daniel.lezcano@linaro.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 23 Jul 2026 12:45:01 +0100, Will Deacon wrote: > > Hi Marc, > > Sorry it took me so long to look at this. No worries, thanks for having given it a look. [...] > > I think this series is a definite improvement on the existing (broken) > code, but there are two things that jump out at me with the new code: > > 1. If somebody uses maxcpus= on perfectly working hardware, they will > run with the overhead of the workaround. I fear this will be > unpopular (and I sympathise!)... I suppose we could wait for people > to scream and then add something like a cmdline option to pinky > promise that the late CPUs are not affected by any timer errata (we > could presumably refuse to bring them online if they are?). I've now added such a command-line option, forcing the counter errata management to be disabled from boot, with a loud warning being produced if we spot that we should have applied something. > > 2. It's a bit grotty that you have to maintain your own mask to track > which CPUs have booted once. I'd have thought this information should > exist already, although none of the existing masks I could find do > quite what you need. One alternative would be to iterate our per-cpu > 'cpu_data' variable or perhaps you could even use the driver's > existing 'arch_timer_evt' variable? Sure, that's easy enough, just slower. Not that it should matter much. I'll post an updated series once I've retested the various configurations. Thanks, M. -- Jazz isn't dead. It just smells funny.