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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A722FC7618E for ; Mon, 24 Apr 2023 13:39:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232672AbjDXNjN (ORCPT ); Mon, 24 Apr 2023 09:39:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232777AbjDXNi7 (ORCPT ); Mon, 24 Apr 2023 09:38:59 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8985B8A4C for ; Mon, 24 Apr 2023 06:38:42 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 28634623BC for ; Mon, 24 Apr 2023 13:38:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DD34C433EF; Mon, 24 Apr 2023 13:38:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1682343521; bh=7n5COy0Bl8pm1WehfnkzFUGniLHZH6BPll5folXoacY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FNkKma257TFdq8y13nbUuyEoPYu1LiNkqrMaromZPjFhQ0niEkt3wcNKMpZ1NNqZN +lccHA5p1h3D1I3ga0819st6BSzYX8WLJwpwMEkaWXqY5bc0JsdRKideyl9R2wbxDc jbXbfCJXELj7jSoG4i78mNY1e16VdHCSY5aNI5xk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, William Breathitt Gray Subject: [PATCH 4.19 27/29] counter: 104-quad-8: Fix race condition between FLAG and CNTR reads Date: Mon, 24 Apr 2023 15:18:54 +0200 Message-Id: <20230424131122.042735111@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230424131121.155649464@linuxfoundation.org> References: <20230424131121.155649464@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: William Breathitt Gray 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; hard-coded maximum count values are replaced by a LS7267_CNTR_MAX define for consistency and clarity. Fixes: 28e5d3bb0325 ("iio: 104-quad-8: Add IIO support for the ACCES 104-QUAD-8") Cc: # 6.1.x Cc: # 6.2.x Link: https://lore.kernel.org/r/20230312231554.134858-1-william.gray@linaro.org/ Signed-off-by: William Breathitt Gray Signed-off-by: Greg Kroah-Hartman --- drivers/iio/counter/104-quad-8.c | 14 +------------- 1 file changed, 1 insertion(+), 13 deletions(-) --- a/drivers/iio/counter/104-quad-8.c +++ b/drivers/iio/counter/104-quad-8.c @@ -61,10 +61,6 @@ 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 { 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 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; /* Reset Byte Pointer; transfer Counter to Output Latch */ outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_CNTR_OUT,