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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 7104BC43219 for ; Fri, 3 May 2019 20:32:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 410772075C for ; Fri, 3 May 2019 20:32:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="bwsPLUjE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727150AbfECUcb (ORCPT ); Fri, 3 May 2019 16:32:31 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:36591 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726480AbfECUc2 (ORCPT ); Fri, 3 May 2019 16:32:28 -0400 Received: by mail-wr1-f65.google.com with SMTP id o4so9366020wra.3 for ; Fri, 03 May 2019 13:32:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=yFWs26NyTQBBHnTLimY9fErMEAAd/wEGYGdh8uiAhr0=; b=bwsPLUjEVmFYODhU+c2MOxzIKK3emyjBG6iCWkMYBqFtQoZdtIYr6hP52/jRNoLJo3 eWFwTsZ2fupPL6Yoij/cbTqbcsRY+MzOnQEEKtNsW53PcpsKck2s4WkmtNdIqAiaXUAy E3mzAvJqLybY/fO/hL8AAASs3qDmwPdkVMzVPx2N1Y41P4Mbq+zvb+n2nkupMjvO1YqX 0kDWD4Vcls4ZVIQ5kCgjh7EeAMPRqNNgVglP9OP3zyMjI8L2apKkMVzj7JNQKHSmwlun gj4oDbVZVohDucTN1kUJOHCyBXUxoVk1ncVAOn3CjBu//3/hgcrBaoVvgGOLCygDOHzl nQrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=yFWs26NyTQBBHnTLimY9fErMEAAd/wEGYGdh8uiAhr0=; b=BcOe0B8u01Oez2E7sNX5JuKkSM7QRtrxNVsM4CcvknqY9hH/klRevYfTlMx7uJZdCz VB0q9l44xhvBevBbpth6M32ncmnqJ2/TRhdPk0YhCHqNvspUZzZSb2NUU/W0XodLSEYz l3fURG29wENLF3nqF1nBLhxvjrylUwN4uWQMp0DK7RGt90RhoO0WhuuNs8K63Ma6+l8E mLDjZWKSMhrTnQ/vnFklNJNu4xX6JNTe5WAOcN53Jqdh4mtuZ49JVjO5apVzbt2ssLh5 3pBD4MjxEtyv8Neo8pm60/WcwvIuvwG1TaG2S+sVrQ4L/biAWXDmbiNCod4GUOdzJWAp ITaQ== X-Gm-Message-State: APjAAAUf5/lmdEEDe+Dl1WyWtx7tINdm52ygqRAWU2PWwOp4eKaUzxoR elCG3X3pNJIvBapQ9XtJYw1r+T0FL78= X-Google-Smtp-Source: APXvYqydkBhECIudeVFVl1XOv4VNXeL9LFJR4eBdis9OQQ3nSkYQIomuAj4y2ShR8eFhfGxf0ZXcjA== X-Received: by 2002:adf:fd04:: with SMTP id e4mr8683562wrr.145.1556915546193; Fri, 03 May 2019 13:32:26 -0700 (PDT) Received: from [192.168.0.41] (sju31-1-78-210-255-2.fbx.proxad.net. [78.210.255.2]) by smtp.googlemail.com with ESMTPSA id e8sm4779602wrc.96.2019.05.03.13.32.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 03 May 2019 13:32:25 -0700 (PDT) Subject: Re: [PATCH 7/7] clocksource/arm_arch_timer: Use arch_timer_read_counter to access stable counters To: Valentin Schneider , Marc Zyngier , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Russell King , Will Deacon , Catalin Marinas , Mark Rutland , Wim Van Sebroeck , Guenter Roeck References: <20190408154907.223536-1-marc.zyngier@arm.com> <20190408154907.223536-8-marc.zyngier@arm.com> <2a60a031-1eab-2d5e-89ff-b5d516545eeb@linaro.org> From: Daniel Lezcano Message-ID: Date: Fri, 3 May 2019 22:32:24 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Valentin, On 30/04/2019 17:39, Valentin Schneider wrote: > Hi, > > On 30/04/2019 16:27, Marc Zyngier wrote: > [...] >>>> @@ -372,6 +392,7 @@ static u32 notrace sun50i_a64_read_cntv_tval_el0(void) >>>> DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround); >>>> EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround); >>>> >>>> +static atomic_t timer_unstable_counter_workaround_in_use = ATOMIC_INIT(0); >>> >>> Wouldn't make sense to READ_ONCE / WRITE_ONCE instead of using an atomic? >> >> I don't think *_ONCE says anything about the atomicity of the access. It >> only instruct the compiler that this should only be accessed once, and >> not reloaded/rewritten. > > FWIW 7bd3e239d6c6 ("locking: Remove atomicy checks from {READ,WRITE}_ONCE") > points this out. Interesting, thanks for the pointer. -- Daniel -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog