From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755210AbeDCIh4 (ORCPT ); Tue, 3 Apr 2018 04:37:56 -0400 Received: from mail-eopbgr40094.outbound.protection.outlook.com ([40.107.4.94]:28608 "EHLO EUR03-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755117AbeDCIhx (ORCPT ); Tue, 3 Apr 2018 04:37:53 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=peda@axentia.se; Subject: Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using dma To: Alexandre Belloni 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 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> <20180403071843.GI14180@piout.net> From: Peter Rosin Organization: Axentia Technologies AB Message-ID: <6a2b49fb-8e2c-ff76-4743-08f8d6a8d5e9@axentia.se> Date: Tue, 3 Apr 2018 10:37:44 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; 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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. Looking at the disassembly, they are gone here (not that I'm fluent). I then tried to compile devmem2 with -O0 (instead of -Os) and the read is then fine. So, I guess the devmem2 devs could claim that it's a buildroot issue, but a volatile would certainly have helped... Cheers, Peter From mboxrd@z Thu Jan 1 00:00:00 1970 From: peda@axentia.se (Peter Rosin) Date: Tue, 3 Apr 2018 10:37:44 +0200 Subject: [PATCH] mtd: nand: raw: atmel: add module param to avoid using dma In-Reply-To: <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> <20180403071843.GI14180@piout.net> Message-ID: <6a2b49fb-8e2c-ff76-4743-08f8d6a8d5e9@axentia.se> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2018-04-03 09:18, Alexandre Belloni wrote: > 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. Looking at the disassembly, they are gone here (not that I'm fluent). I then tried to compile devmem2 with -O0 (instead of -Os) and the read is then fine. So, I guess the devmem2 devs could claim that it's a buildroot issue, but a volatile would certainly have helped... Cheers, Peter