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=-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=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 5C5A8C4332D for ; Mon, 28 Dec 2020 14:08:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 26461207A9 for ; Mon, 28 Dec 2020 14:08:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2438574AbgL1OID (ORCPT ); Mon, 28 Dec 2020 09:08:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:42334 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2438545AbgL1OHz (ORCPT ); Mon, 28 Dec 2020 09:07:55 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 408CE20731; Mon, 28 Dec 2020 14:07:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609164432; bh=hs3e2zPi1RaqwgroejTdVMzBsqV1hwk0x5DiuiTIvPU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nYk+XMZ2KKNMkSQ0dxbi+ZdYPIR0LlvjO/Yef/gdzkpnjZEdJyzZFrvub2mOSEWQs hdjiQWepTjtgTB6lc/WAloJPk072Ai6VCSBZDWt5UXpo+u55IXNdD1JLkI9SrJgWXK +lXzwXn8MU25PIDC5wPkT8I9rNC3gXM539Zg1xFI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, David Jander , Oleksij Rempel , Dmitry Torokhov , Sasha Levin Subject: [PATCH 5.10 148/717] Input: ads7846 - fix integer overflow on Rt calculation Date: Mon, 28 Dec 2020 13:42:26 +0100 Message-Id: <20201228125028.053390822@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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Oleksij Rempel [ Upstream commit 820830ec918f6c3dcd77a54a1c6198ab57407916 ] In some rare cases the 32 bit Rt value will overflow if z2 and x is max, z1 is minimal value and x_plate_ohms is relatively high (for example 800 ohm). This would happen on some screen age with low pressure. There are two possible fixes: - make Rt 64bit - reorder calculation to avoid overflow The second variant seems to be preferable, since 64 bit calculation on 32 bit system is a bit more expensive. Fixes: ffa458c1bd9b6f653008d450f337602f3d52a646 ("spi: ads7846 driver") Co-developed-by: David Jander Signed-off-by: David Jander Signed-off-by: Oleksij Rempel Link: https://lore.kernel.org/r/20201113112240.1360-1-o.rempel@pengutronix.de Signed-off-by: Dmitry Torokhov Signed-off-by: Sasha Levin --- drivers/input/touchscreen/ads7846.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c index 69992d5e53118..78ed285c27ae3 100644 --- a/drivers/input/touchscreen/ads7846.c +++ b/drivers/input/touchscreen/ads7846.c @@ -802,10 +802,11 @@ static void ads7846_report_state(struct ads7846 *ts) /* compute touch pressure resistance using equation #2 */ Rt = z2; Rt -= z1; - Rt *= x; Rt *= ts->x_plate_ohms; + Rt = DIV_ROUND_CLOSEST(Rt, 16); + Rt *= x; Rt /= z1; - Rt = (Rt + 2047) >> 12; + Rt = DIV_ROUND_CLOSEST(Rt, 256); } else { Rt = 0; } -- 2.27.0