From patchwork Mon Dec 28 12:47:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 353501 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, USER_AGENT_GIT autolearn=unavailable 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 34CA0C43381 for ; Mon, 28 Dec 2020 14:47:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 012D3207B2 for ; Mon, 28 Dec 2020 14:47:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2502884AbgL1OXp (ORCPT ); Mon, 28 Dec 2020 09:23:45 -0500 Received: from mail.kernel.org ([198.145.29.99]:59756 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2502875AbgL1OXp (ORCPT ); Mon, 28 Dec 2020 09:23:45 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id ED6E120791; Mon, 28 Dec 2020 14:23:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609165384; bh=dKFIqJAkreP7x4OwIFF3ICRl8vZM4yI8GJOz+q8JmpM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VGKBdZtvTAHf5g0Qqb/997Rs8zyrDcpDHXvAxmhn4foxBZ3vtn8dQFyJUW6FontRU vVallKgODw9tDq7ZxBEiaTCmeKQkDbciMX8SkdmmYI/xgyUVGI4WQB/K5aNqZjBusT L2PTCkm6LoZ7P3KHJw7dTrE0cK+6jp1LjBebMfAc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= , Johannes Pointner , Thierry Reding , Sasha Levin Subject: [PATCH 5.10 481/717] pwm: imx27: Fix overflow for bigger periods Date: Mon, 28 Dec 2020 13:47:59 +0100 Message-Id: <20201228125044.013444789@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201228125020.963311703@linuxfoundation.org> References: <20201228125020.963311703@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Uwe Kleine-König [ Upstream commit 1ce65396e6b2386b4fd54f87beff0647a772e1cd ] The second parameter of do_div is an u32 and NSEC_PER_SEC * prescale overflows this for bigger periods. Assuming the usual pwm input clk rate of 66 MHz this happens starting at requested period > 606060 ns. Splitting the division into two operations doesn't loose any precision. It doesn't need to be feared that c / NSEC_PER_SEC doesn't fit into the unsigned long variable "duty_cycles" because in this case the assignment above to period_cycles would already have been overflowing as period >= duty_cycle and then the calculation is moot anyhow. Fixes: aef1a3799b5c ("pwm: imx27: Fix rounding behavior") Signed-off-by: Uwe Kleine-König Tested-by: Johannes Pointner Signed-off-by: Thierry Reding Signed-off-by: Sasha Levin --- drivers/pwm/pwm-imx27.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index c50d453552bd4..86bcafd23e4f6 100644 --- a/drivers/pwm/pwm-imx27.c +++ b/drivers/pwm/pwm-imx27.c @@ -235,8 +235,9 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, period_cycles /= prescale; c = clkrate * state->duty_cycle; - do_div(c, NSEC_PER_SEC * prescale); + do_div(c, NSEC_PER_SEC); duty_cycles = c; + duty_cycles /= prescale; /* * according to imx pwm RM, the real period value should be PERIOD