From patchwork Fri Feb 19 14:45:36 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Peter Maydell X-Patchwork-Id: 12095535 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=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 720A3C433E0 for ; Fri, 19 Feb 2021 14:53:26 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 F36A964E33 for ; Fri, 19 Feb 2021 14:53:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F36A964E33 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:44412 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lD79p-0000Sl-1J for qemu-devel@archiver.kernel.org; Fri, 19 Feb 2021 09:53:25 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33380) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lD73C-00020Q-OK for qemu-devel@nongnu.org; Fri, 19 Feb 2021 09:46:34 -0500 Received: from mail-wm1-x332.google.com ([2a00:1450:4864:20::332]:40327) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1lD734-0003MF-Jx for qemu-devel@nongnu.org; Fri, 19 Feb 2021 09:46:34 -0500 Received: by mail-wm1-x332.google.com with SMTP id o24so7861444wmh.5 for ; Fri, 19 Feb 2021 06:46:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:subject:date:message-id:in-reply-to:references:mime-version :content-transfer-encoding; bh=a11pg5cH1ykxEu6V8jLMW9ZxX3RV9/5IG0HAgyAT898=; b=bNDZxpGNQsX9JBhRw6fzBVnXo3cFurIa2B5ma421Md8RwMwQ0pMkZqCEc5cPQtAxEk PZ2N0LHEHw8/5vZUv6EjarjI4dY8fo1WrjE/RmpTk5p3CTY4u+EzfksFTnMbsxF/E8lz l5o9Zt0N+5GsT3p+2b+k7ScBhWq8moirp7mEJZAAIB4C6UTajw/y9Xgj1b3DZISIiNd1 02iUzrEX2BUwDNLH3t46oYRaQJRQuUNaUQPklEaCFGhFZ0q3QnC53Jpk7+0v+fyuxyoB I/G3pR4g2nCLinZ2IxVmYrLlZftK5qH/RpMYxyQofdQyL1w6LW/2eiBAbMs6aU6y4e83 rEdw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=a11pg5cH1ykxEu6V8jLMW9ZxX3RV9/5IG0HAgyAT898=; b=gLqYAXOkxLq5lANduZ7uNq9orU2molk2ZYg7taSh8wP5TbijgaANl3YTbRGKYpMbpY Rw4Wdv5PZ+NVafL03xdVzf0yjEfscRPKEDXPmcUh2AelqQuVXr8W1FkYDM/cpcrEG3Sb 2amV/2X4zLUDWZt3ku/q+rQKpKQFP0RSyoK4+DDx5IMIf38XfqxgKUHVay1urvugo3/M 2vOejjUd+mXl1ntQvzYIZbj81aJfoofvO6bk03l2TmVAhuFOQ1KNgc9W2iG5nwqoPjzs 4kPDVZuwzOYaVVwzJ8bHClMkS2V6F559q4AlMuSXzBq8j9GDJC+eSNoGYTS6y79vkd13 DTig== X-Gm-Message-State: AOAM533NoijMi8reh0eJta8BF902JWrOYn+1mH6fYbZEgfy+LZBzkNRb 51+8keSDXv9G6Sxpx7n5kHY3cl97LbU3ng== X-Google-Smtp-Source: ABdhPJzazil8Coabza58SvKcUBklDyCHd9xjgWWNJWsUWx0bQYn1QyPpf5ZoqhJOjjWWHROaGwUtuw== X-Received: by 2002:a05:600c:20f:: with SMTP id 15mr1315419wmi.88.1613745982798; Fri, 19 Feb 2021 06:46:22 -0800 (PST) Received: from orth.archaic.org.uk (orth.archaic.org.uk. [81.2.115.148]) by smtp.gmail.com with ESMTPSA id q18sm2263628wrw.91.2021.02.19.06.46.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Feb 2021 06:46:22 -0800 (PST) From: Peter Maydell To: qemu-arm@nongnu.org, qemu-devel@nongnu.org Subject: [PATCH 03/44] clock: Add clock_ns_to_ticks() function Date: Fri, 19 Feb 2021 14:45:36 +0000 Message-Id: <20210219144617.4782-4-peter.maydell@linaro.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210219144617.4782-1-peter.maydell@linaro.org> References: <20210219144617.4782-1-peter.maydell@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::332; envelope-from=peter.maydell@linaro.org; helo=mail-wm1-x332.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Add a clock_ns_to_ticks() function which does the opposite of clock_ticks_to_ns(): given a duration in nanoseconds, it returns the number of clock ticks that would happen in that time. This is useful for devices that have a free running counter register whose value can be calculated when it is read. Signed-off-by: Peter Maydell Reviewed-by: Luc Michel Reviewed-by: Hao Wu Tested-by: Philippe Mathieu-Daudé --- docs/devel/clocks.rst | 12 ++++++++++++ include/hw/clock.h | 41 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 53 insertions(+) diff --git a/docs/devel/clocks.rst b/docs/devel/clocks.rst index f0391e76b4f..956bd147ea0 100644 --- a/docs/devel/clocks.rst +++ b/docs/devel/clocks.rst @@ -360,6 +360,18 @@ rather than simply passing it to a QEMUTimer function like ``timer_mod_ns()`` then you should be careful to avoid overflow in those calculations, of course.) +Obtaining tick counts +--------------------- + +For calculations where you need to know the number of ticks in +a given duration, use ``clock_ns_to_ticks()``. This function handles +possible non-whole-number-of-nanoseconds periods and avoids +potential rounding errors. It will return '0' if the clock is stopped +(i.e. it has period zero). If the inputs imply a tick count that +overflows a 64-bit value (a very long duration for a clock with a +very short period) the output value is truncated, so effectively +the 64-bit output wraps around. + Changing a clock period ----------------------- diff --git a/include/hw/clock.h b/include/hw/clock.h index 2ba44e14424..a7187eab95e 100644 --- a/include/hw/clock.h +++ b/include/hw/clock.h @@ -286,6 +286,47 @@ static inline uint64_t clock_ticks_to_ns(const Clock *clk, uint64_t ticks) return ns_low >> 32 | ns_high << 32; } +/** + * clock_ns_to_ticks: + * @clk: the clock to query + * @ns: duration in nanoseconds + * + * Returns the number of ticks this clock would make in the given + * number of nanoseconds. Because a clock can have a period which + * is not a whole number of nanoseconds, it is important to use this + * function rather than attempting to obtain a "period in nanoseconds" + * value and then dividing the duration by that value. + * + * If the clock is stopped (ie it has period zero), returns 0. + * + * For some inputs the result could overflow a 64-bit value (because + * the clock's period is short and the duration is long). In these + * cases we truncate the result to a 64-bit value. This is on the + * assumption that generally the result is going to be used to report + * a 32-bit or 64-bit guest register value, so wrapping either cannot + * happen or is the desired behaviour. + */ +static inline uint64_t clock_ns_to_ticks(const Clock *clk, uint64_t ns) +{ + /* + * ticks = duration_in_ns / period_in_ns + * = ns / (period / 2^32) + * = (ns * 2^32) / period + * The hi, lo inputs to divu128() are (ns << 32) as a 128 bit value. + */ + uint64_t lo = ns << 32; + uint64_t hi = ns >> 32; + if (clk->period == 0) { + return 0; + } + /* + * Ignore divu128() return value as we've caught div-by-zero and don't + * need different behaviour for overflow. + */ + divu128(&lo, &hi, clk->period); + return lo; +} + /** * clock_is_enabled: * @clk: a clock