From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755114AbeDCHSr (ORCPT ); Tue, 3 Apr 2018 03:18:47 -0400 Received: from mail.bootlin.com ([62.4.15.54]:37025 "EHLO mail.bootlin.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754938AbeDCHSp (ORCPT ); Tue, 3 Apr 2018 03:18:45 -0400 Date: Tue, 3 Apr 2018 09:18:43 +0200 From: Alexandre Belloni To: Peter Rosin Cc: Boris Brezillon , Josh Wu , Cyrille Pitchen , linux-kernel@vger.kernel.org, Nicolas Ferre , Marek Vasut , linux-mtd@lists.infradead.org, Richard Weinberger , Brian Norris , David Woodhouse , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using dma Message-ID: <20180403071843.GI14180@piout.net> References: <20180329131054.22506-1-peda@axentia.se> <20180329153322.5e2fc1e7@bbrezillon> <20180329154416.5c1a0013@bbrezillon> <20180402142249.7e076a64@bbrezillon> <20180402212843.164d5d21@bbrezillon> <8e35701f-1bfa-c9c0-62e6-48ed19d7ba37@axentia.se> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8e35701f-1bfa-c9c0-62e6-48ed19d7ba37@axentia.se> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/04/2018 at 22:23:17 +0200, Peter Rosin wrote: > >> No, but did it again and checked, see transcript below. > > > > I don't use devmem2. Is 'readback' information accurate or is it > > always what's been written? Because when you write 0x33 to 0xFFFFECBC, > > 0x33 is read back, but just after that, when you read it again it's 0. > > Looking at the devmem2 source, it seems very likely that the compiler > optimizes out the read and thus outputs what has been written. > At least on x86, it is not optimized out. -- Alexandre Belloni, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com