From patchwork Sun Mar 12 23:15:50 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: William Breathitt Gray X-Patchwork-Id: 13171890 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 C87A2C74A4B for ; Sun, 12 Mar 2023 23:16:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229745AbjCLXQR (ORCPT ); Sun, 12 Mar 2023 19:16:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38058 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229677AbjCLXQO (ORCPT ); Sun, 12 Mar 2023 19:16:14 -0400 Received: from mail-qt1-x82f.google.com (mail-qt1-x82f.google.com [IPv6:2607:f8b0:4864:20::82f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9E50D26CE4 for ; Sun, 12 Mar 2023 16:16:12 -0700 (PDT) Received: by mail-qt1-x82f.google.com with SMTP id c19so11508281qtn.13 for ; Sun, 12 Mar 2023 16:16:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1678662971; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=R1ENeaBfRz6SWrwdqP2MAd7R+kpBfK8pfsSO8vxDCF0=; b=CfV0zlBWYVHfuG5Ac+jwlt2TyojmiibFnT65yzVqZ/bbCmqN8gjkqSx87zXSHMI7J6 pzexBwB0OcS21QFryblC5W0RSnCK6/a3XpwlMFr3kPmFdA1NjUyMi3EO18p3Z33vRDDu DFE7d4afmp7NG8W6v4Ugu4zRfsTlfKCw8lK3MfvooXhZvggxf8ERYE8AskTSwJf5Rh2E 1AmUOgdq2Qv8Md0ghQGk9kHbnfzyCuzQ/+MIznuPv9KAj3pqKFyrXxbCUT4uZVZHJOG7 ky2xqW2wto1zSSfFCEd23y7QmAd46blC6Ssfm5c4JTGV+fWluybV7JIX1QjNfD1ums/9 sTIA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678662971; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=R1ENeaBfRz6SWrwdqP2MAd7R+kpBfK8pfsSO8vxDCF0=; b=bN/t7yILzp4Q9IaXAIrKWIIGjWOKizon3DKj89G5NpE+GU/V+UT5BtZv/qY1WNH3ZP BJRib9PX4WSTdNGPAlmcYdl+WleyHBM6Lwr0LzHRxC//UVIomP61EJdR4NuvkjEqIZfK vZO5xMX1IXMGqjgjCiGSHDvDpU6HPRh8qOc+OACP6j6pyK8kCswNaQZYAyo4s8cgRzIm I5DxWxHip56PmiNzAMeDz2fWhdabR36mKVgZYpctNIRCWyOfCnQslr7yAc/5Xwy6lbzj nJEgoffEJAipNwp6CTZXC+c3pz1eIlBRAmbXcEM+w0bvRL6ipIJfJyWPZZXvPjk53kOJ XBlg== X-Gm-Message-State: AO0yUKXUf3+VXlsfu9ykXsUzOUbU9CCU+CdXqw8QYTZIge6Swa28hSP1 DUUBH61w24iYIC/2jvClusZf/yufNAoJNk9lx/o= X-Google-Smtp-Source: AK7set9Zfnrah355ZP1Aoeye8QsXsctxC9ULMjRB5Vo95kUCOK8f40n+jxmPo1oZ4x4qKVaonfbvVA== X-Received: by 2002:ac8:574d:0:b0:3bf:be8a:8f96 with SMTP id 13-20020ac8574d000000b003bfbe8a8f96mr15791823qtx.12.1678662971478; Sun, 12 Mar 2023 16:16:11 -0700 (PDT) Received: from fedora.attlocal.net (69-109-179-158.lightspeed.dybhfl.sbcglobal.net. [69.109.179.158]) by smtp.gmail.com with ESMTPSA id dm21-20020a05620a1d5500b00742f250ebc0sm4307091qkb.9.2023.03.12.16.16.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 12 Mar 2023 16:16:11 -0700 (PDT) From: William Breathitt Gray To: linux-iio@vger.kernel.org Cc: linux-kernel@vger.kernel.org, jic23@kernel.org, lars@metafoo.de, William Breathitt Gray , stable@vger.kernel.org Subject: [PATCH 5.15 v3 2/6] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads Date: Sun, 12 Mar 2023 19:15:50 -0400 Message-Id: <20230312231554.134858-2-william.gray@linaro.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230312231554.134858-1-william.gray@linaro.org> References: <20230312231554.134858-1-william.gray@linaro.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org The Counter (CNTR) register is 24 bits wide, but we can have an effective 25-bit count value by setting bit 24 to the XOR of the Borrow flag and Carry flag. The flags can be read from the FLAG register, but a race condition exists: the Borrow flag and Carry flag are instantaneous and could change by the time the count value is read from the CNTR register. Since the race condition could result in an incorrect 25-bit count value, remove support for 25-bit count values from this driver. Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8") Cc: # 5.15.x Signed-off-by: William Breathitt Gray --- drivers/counter/104-quad-8.c | 18 +++--------------- 1 file changed, 3 insertions(+), 15 deletions(-) base-commit: bbf9f29bac04f85bbf45af172dcdc9664d8808cb diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c index 0caa60537..643aae0c9 100644 --- a/drivers/counter/104-quad-8.c +++ b/drivers/counter/104-quad-8.c @@ -61,10 +61,6 @@ struct quad8 { #define QUAD8_REG_CHAN_OP 0x11 #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16 #define QUAD8_DIFF_ENCODER_CABLE_STATUS 0x17 -/* Borrow Toggle flip-flop */ -#define QUAD8_FLAG_BT BIT(0) -/* Carry Toggle flip-flop */ -#define QUAD8_FLAG_CT BIT(1) /* Error flag */ #define QUAD8_FLAG_E BIT(4) /* Up/Down flag */ @@ -121,17 +117,9 @@ static int quad8_count_read(struct counter_device *counter, { struct quad8 *const priv = counter->priv; const int base_offset = priv->base + 2 * count->id; - unsigned int flags; - unsigned int borrow; - unsigned int carry; int i; - flags = inb(base_offset + 1); - borrow = flags & QUAD8_FLAG_BT; - carry = !!(flags & QUAD8_FLAG_CT); - - /* Borrow XOR Carry effectively doubles count range */ - *val = (unsigned long)(borrow ^ carry) << 24; + *val = 0; mutex_lock(&priv->lock); @@ -699,8 +687,8 @@ static ssize_t quad8_count_ceiling_read(struct counter_device *counter, mutex_unlock(&priv->lock); - /* By default 0x1FFFFFF (25 bits unsigned) is maximum count */ - return sprintf(buf, "33554431\n"); + /* By default 0xFFFFFF (24 bits unsigned) is maximum count */ + return sprintf(buf, "16777215\n"); } static ssize_t quad8_count_ceiling_write(struct counter_device *counter,