From patchwork Fri Jun 30 18:38:35 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Reichel X-Patchwork-Id: 13298678 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5FDB3EB64D7 for ; Fri, 30 Jun 2023 18:38:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229774AbjF3Sit (ORCPT ); Fri, 30 Jun 2023 14:38:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229537AbjF3Sis (ORCPT ); Fri, 30 Jun 2023 14:38:48 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7BB4A107; Fri, 30 Jun 2023 11:38:47 -0700 (PDT) Received: from jupiter.universe (dyndsl-091-248-211-174.ewe-ip-backbone.de [91.248.211.174]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: sre) by madras.collabora.co.uk (Postfix) with ESMTPSA id E66F166057EC; Fri, 30 Jun 2023 19:38:45 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1688150326; bh=LWbgAgL+0OeJkzIKUoalbJkby80mrv5r7CnJUPH2mrs=; h=From:To:Cc:Subject:Date:From; b=NCmbEp6ER6YWuWpoNCK2+86vlAbKNIPyJjilUJ9c0bYZcvFMnnHcb2fmB1TSEcJo/ my3vEVqUZv9K81TYQun3aBqL0Q4k+kBln3s9ETbnKWuDpluF6HOrgH5XtHCPOgziJV MutuZ4OLC6B+3J/Ota9pXiDHYWV7+btslQL6QgJYz8iKkPTHAC3/U+aihunWonCuHE rvdQ6S6qmRrjkAn+6N1U/kXlmCUY/8qQ/Aql5W55Vcsy55Ocnr9CuVtf+AqUwbhzAr 37xb0XoS46/tG3Qkbhmgmj05FBTbk5nXcps8CavJYfTaRztpijLw+nxkC/Sk0U76J6 Hvgh0O4HiasNg== Received: by jupiter.universe (Postfix, from userid 1000) id A9EEC487A17; Fri, 30 Jun 2023 20:38:43 +0200 (CEST) From: Sebastian Reichel To: Michael Turquette , Stephen Boyd , David Laight , linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Sebastian Reichel , kernel@collabora.com Subject: [PATCH v3 1/1] clk: divider: Fix divisor masking on 64 bit platforms Date: Fri, 30 Jun 2023 20:38:35 +0200 Message-Id: <20230630183835.464216-1-sebastian.reichel@collabora.com> X-Mailer: git-send-email 2.40.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-clk@vger.kernel.org The clock framework handles clock rates as "unsigned long", so u32 on 32-bit architectures and u64 on 64-bit architectures. The current code casts the dividend to u64 on 32-bit to avoid a potential overflow. For example DIV_ROUND_UP(3000000000, 1500000000) = (3.0G + 1.5G - 1) / 1.5G = = OVERFLOW / 1.5G, which has been introduced in commit 9556f9dad8f5 ("clk: divider: handle integer overflow when dividing large clock rates"). On 64 bit platforms this masks the divisor, so that only the lower 32 bit are used. Thus requesting a frequency >= 4.3GHz results in incorrect values. For example requesting 4300000000 (4.3 GHz) will effectively request ca. 5 MHz. Requesting clk_round_rate(clk, ULONG_MAX) is a bit of a special case, since that still returns correct values as long as the parent clock is below 8.5 GHz. Fix this by introducing a new helper, which avoids the overflow by using a modulo operation instead of math tricks. This avoids any requirements on the arguments (except that divisor should not be 0 obviously). Signed-off-by: Sebastian Reichel --- Changes since PATCHv2: * https://lore.kernel.org/all/20230526171057.66876-1-sebastian.reichel@collabora.com/ * Drop first patch (applied) * Update second patch to use newly introduced DIV_ROUND_UP_NO_OVERFLOW Changes since PATCHv1: * https://lore.kernel.org/linux-clk/20230519190522.194729-1-sebastian.reichel@collabora.com/ * Add Christopher Obbard's Reviewed-by to the first patch * Update the second patch to use DIV_ROUND_UP instead of DIV64_U64_ROUND_UP --- drivers/clk/clk-divider.c | 6 +++--- include/linux/math.h | 11 +++++++++++ 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index a2c2b5203b0a..94b4fb66a60f 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -220,7 +220,7 @@ static int _div_round_up(const struct clk_div_table *table, unsigned long parent_rate, unsigned long rate, unsigned long flags) { - int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate); + int div = DIV_ROUND_UP_NO_OVERFLOW(parent_rate, rate); if (flags & CLK_DIVIDER_POWER_OF_TWO) div = __roundup_pow_of_two(div); @@ -237,7 +237,7 @@ static int _div_round_closest(const struct clk_div_table *table, int up, down; unsigned long up_rate, down_rate; - up = DIV_ROUND_UP_ULL((u64)parent_rate, rate); + up = DIV_ROUND_UP_NO_OVERFLOW(parent_rate, rate); down = parent_rate / rate; if (flags & CLK_DIVIDER_POWER_OF_TWO) { @@ -473,7 +473,7 @@ int divider_get_val(unsigned long rate, unsigned long parent_rate, { unsigned int div, value; - div = DIV_ROUND_UP_ULL((u64)parent_rate, rate); + div = DIV_ROUND_UP_NO_OVERFLOW(parent_rate, rate); if (!_is_valid_div(table, div, flags)) return -EINVAL; diff --git a/include/linux/math.h b/include/linux/math.h index 2d388650c556..cf14d436fc2e 100644 --- a/include/linux/math.h +++ b/include/linux/math.h @@ -36,6 +36,17 @@ #define DIV_ROUND_UP __KERNEL_DIV_ROUND_UP +/** + * DIV_ROUND_UP_NO_OVERFLOW - divide two numbers and always round up + * @n: numerator / dividend + * @d: denominator / divisor + * + * This functions does the same as DIV_ROUND_UP, but internally uses a + * division and a modulo operation instead of math tricks. This way it + * avoids overflowing when handling big numbers. + */ +#define DIV_ROUND_UP_NO_OVERFLOW(n, d) (((n) / (d)) + !!((n) % (d))) + #define DIV_ROUND_DOWN_ULL(ll, d) \ ({ unsigned long long _tmp = (ll); do_div(_tmp, d); _tmp; })