From patchwork Mon Apr 24 16:01:04 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: 13222339 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 87B82C77B7F for ; Mon, 24 Apr 2023 16:01:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231396AbjDXQBS (ORCPT ); Mon, 24 Apr 2023 12:01:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231781AbjDXQBP (ORCPT ); Mon, 24 Apr 2023 12:01:15 -0400 Received: from mail-ej1-x629.google.com (mail-ej1-x629.google.com [IPv6:2a00:1450:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 97A636A63 for ; Mon, 24 Apr 2023 09:01:13 -0700 (PDT) Received: by mail-ej1-x629.google.com with SMTP id a640c23a62f3a-95678d891d6so791987266b.1 for ; Mon, 24 Apr 2023 09:01:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1682352072; x=1684944072; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=ItXk9sOTul8nHcQoQ5OMTNAOIPvFkgfn2LiOsp6dVh0=; b=A98E6RSSxhUqhBadttwvToEIPQtUZ0mPjxzjyU/Mim0Lf27+ucjlh9vx5EJpiAKR9o s+VdC3LYCGvdDbRpjZqaAaJRDEzr6ZqeulhvVhZ+ked7yhukf0hOni56WkJ2NQTaWBoi wQPgSyFBDgbWNtUId7uZ1HKtmQGE2jusMyJvgpeHu2Tz+MJT8aPBtLWcArcxM5nD+HAJ 6Ct5Mlz2q8bbcCl8cNYDXzcBOxgHl7nFNuR/WcHJMiRBuHiArPbpfe4HpruRSOriA3s/ xigazvQbMa0by/5CgQwhdGjhT3zeq3J5PK87PMEZwEU//gqYN1lp+5KqNhEL4cFFRkaV j37A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1682352072; x=1684944072; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=ItXk9sOTul8nHcQoQ5OMTNAOIPvFkgfn2LiOsp6dVh0=; b=S3CGhPT1hyDQ248v1M955QbTtfsPXYvMmXHT3fyQwb6upqJ6teHIVcSulNxgUJf8rK LPlYfhMn1ZcAslU0XmTxsFcgIsX8PemMxiBLZfBTcek1XGK3EIpy5F4vv+/4lj9hO8my 2YionYnFZlSY1tXDS8v5ip/FN8ZruHid+SJGRIsZE4kVJ9MuJuCa6QBX9ZHYSkQqUbQn G1z0UMZj3s+XbcRf9l1FLfw8JKD+/OkiMid0ObNeDpRU6tyB+lTYSxBxNxVrJCJ5mYP2 BQmYtdh6psh2V1R1EeteJ1qnSUoOEH8ln+zKQdDEMsAHqbBULoC+8n+S5xB8WVBa/eDg RTJg== X-Gm-Message-State: AAQBX9cWj8gKamB70y3Bs4+Kgk6z1FGNIn4TGoyPnrz4sPBbwKt9CxhU v9Lt7s9pOr8pvlKNSI1S0kCrwQ== X-Google-Smtp-Source: AKy350a+fhIV7M5cXo7+HmyMP6SNbnABDOalrjajHuvMxEIjPJCMkgiw02UjrpIcuXQxRcLwA+5IRQ== X-Received: by 2002:a17:907:6d24:b0:94a:9f9a:b3c4 with SMTP id sa36-20020a1709076d2400b0094a9f9ab3c4mr11161282ejc.49.1682352071911; Mon, 24 Apr 2023 09:01:11 -0700 (PDT) Received: from fedora.. ([195.167.132.10]) by smtp.gmail.com with ESMTPSA id g10-20020a170906594a00b008cecb8f374asm5665879ejr.0.2023.04.24.09.01.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Apr 2023 09:01:11 -0700 (PDT) From: William Breathitt Gray To: Greg Kroah-Hartman Cc: linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, Jonathan Cameron , William Breathitt Gray , stable@vger.kernel.org Subject: [PATCH 5.4 v5 1/2] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads Date: Mon, 24 Apr 2023 12:01:04 -0400 Message-Id: <20230424160106.4415-1-william.gray@linaro.org> X-Mailer: git-send-email 2.40.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org commit 4aa3b75c74603c3374877d5fd18ad9cc3a9a62ed upstream. 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: # 5.4.x Signed-off-by: William Breathitt Gray --- drivers/counter/104-quad-8.c | 30 ++++-------------------------- 1 file changed, 4 insertions(+), 26 deletions(-) base-commit: 58f42ed1cd31238745bddd943c4f5849dc83a2ac diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c index f261a57af1c..919d6f1ced8 100644 --- a/drivers/counter/104-quad-8.c +++ b/drivers/counter/104-quad-8.c @@ -57,10 +57,6 @@ struct quad8_iio { #define QUAD8_REG_CHAN_OP 0x11 #define QUAD8_REG_INDEX_INPUT_LEVELS 0x16 -/* 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 */ @@ -97,9 +93,6 @@ static int quad8_read_raw(struct iio_dev *indio_dev, { struct quad8_iio *const priv = iio_priv(indio_dev); const int base_offset = priv->base + 2 * chan->channel; - unsigned int flags; - unsigned int borrow; - unsigned int carry; int i; switch (mask) { @@ -110,12 +103,7 @@ static int quad8_read_raw(struct iio_dev *indio_dev, return IIO_VAL_INT; } - flags = inb(base_offset + 1); - borrow = flags & QUAD8_FLAG_BT; - carry = !!(flags & QUAD8_FLAG_CT); - - /* Borrow XOR Carry effectively doubles count range */ - *val = (borrow ^ carry) << 24; + *val = 0; mutex_lock(&priv->lock); @@ -639,19 +627,9 @@ static int quad8_count_read(struct counter_device *counter, { struct quad8_iio *const priv = counter->priv; const int base_offset = priv->base + 2 * count->id; - unsigned int flags; - unsigned int borrow; - unsigned int carry; - unsigned long position; + unsigned long position = 0; int i; - flags = inb(base_offset + 1); - borrow = flags & QUAD8_FLAG_BT; - carry = !!(flags & QUAD8_FLAG_CT); - - /* Borrow XOR Carry effectively doubles count range */ - position = (unsigned long)(borrow ^ carry) << 24; - mutex_lock(&priv->lock); /* Reset Byte Pointer; transfer Counter to Output Latch */ @@ -1204,8 +1182,8 @@ 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,