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Tue, 27 Mar 2018 08:00:10 -0400 Received: from mga06.intel.com ([134.134.136.31]:15056 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751187AbeC0MAK (ORCPT ); Tue, 27 Mar 2018 08:00:10 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.48,367,1517904000"; d="scan'208";a="215253902" Date: Tue, 27 Mar 2018 17:34:23 +0530 From: Vinod Koul To: Maxime Jayat Cc: Ludovic Desroches , Nicolas Ferre , Dan Williams , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] dmaengine: at_xdmac: fix rare residue corruption Message-ID: <20180327120422.GJ15443@localhost> References: <20180222113955.4043-1-maxime.jayat@mobile-devices.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180222113955.4043-1-maxime.jayat@mobile-devices.fr> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Feb 22, 2018 at 12:39:55PM +0100, Maxime Jayat wrote: > Despite the efforts made to correctly read the NDA and CUBC registers, > the order in which the registers are read could sometimes lead to an > inconsistent state. > > Re-using the timeline from the comments, this following timing of > registers reads could lead to reading NDA with value "@desc2" and > CUBC with value "MAX desc1": > > INITD -------- ------------ > |____________________| > _______________________ _______________ > NDA @desc2 \/ @desc3 > _______________________/\_______________ > __________ ___________ _______________ > CUBC 0 \/ MAX desc1 \/ MAX desc2 > __________/\___________/\_______________ > | | | | > Events:(1)(2) (3)(4) > > (1) check_nda = @desc2 > (2) initd = 1 > (3) cur_ubc = MAX desc1 > (4) cur_nda = @desc2 > > This is allowed by the condition ((check_nda == cur_nda) && initd), > despite cur_ubc and cur_nda being in the precise state we don't want. > > This error leads to incorrect residue computation. > > Fix it by inversing the order in which CUBC and INITD are read. This > makes sure that NDA and CUBC are always read together either _before_ > INITD goes to 0 or _after_ it is back at 1. > The case where NDA is read before INITD is at 0 and CUBC is read after > INITD is back at 1 will be rejected by check_nda and cur_nda being > different. Applied, thanks -- ~Vinod