Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754662Ab2JEIxR (ORCPT ); Fri, 5 Oct 2012 04:53:17 -0400 Received: from arroyo.ext.ti.com ([192.94.94.40]:57492 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754277Ab2JEIxM convert rfc822-to-8bit (ORCPT ); Fri, 5 Oct 2012 04:53:12 -0400 From: "Philip, Avinash" To: Ivan Djelic CC: "dwmw2@infradead.org" , "artem.bityutskiy@linux.intel.com" , "tony@atomide.com" , "Mohammed, Afzal" , "linux-mtd@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-omap@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-doc@vger.kernel.org" , "devicetree-discuss@lists.ozlabs.org" Subject: RE: [PATCH 4/4] mtd: nand: omap2: Add data correction support Thread-Topic: [PATCH 4/4] mtd: nand: omap2: Add data correction support Thread-Index: AQHNoXboDgXHKDcq00CaQ0Yo4e+M+penmT6AgAFWaxCAAWegIA== Date: Fri, 5 Oct 2012 08:51:50 +0000 Deferred-Delivery: Fri, 5 Oct 2012 08:51:00 +0000 Message-ID: <518397C60809E147AF5323E0420B992E3E9B8A65@DBDE01.ent.ti.com> References: <1349274589-11389-1-git-send-email-avinashphilip@ti.com> <1349274589-11389-5-git-send-email-avinashphilip@ti.com> <20121003192044.GB27502@parrot.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [172.24.170.142] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3047 Lines: 70 On Thu, Oct 04, 2012 at 15:51:03, Philip, Avinash wrote: > On Thu, Oct 04, 2012 at 00:50:45, Ivan Djelic wrote: > > On Wed, Oct 03, 2012 at 03:29:49PM +0100, Philip, Avinash wrote: > > > ELM module can be used for error correction of BCH 4 & 8 bit. Also > > > support read & write page in one shot by adding custom read_page & > > > write_page methods. This helps in optimizing code. > > > > > > New structure member "is_elm_used" is added to know the status of > > > whether the ELM module is used for error correction or not. > > > > > > Note: > > > ECC layout of BCH8 uses 14 bytes for 512 byte of data to make compatible > > > with RBL ECC layout, even though the requirement was only 13 byte. This > > > results a common ecc layout across RBL, U-boot & Linux. > > > > > > > See a few comments below, > > > > (...) > > > +static int omap_elm_correct_data(struct mtd_info *mtd, u_char *dat, > > > + u_char *read_ecc, u_char *calc_ecc) > > > +{ > > > + struct omap_nand_info *info = container_of(mtd, struct omap_nand_info, > > > + mtd); > > > + int eccsteps = info->nand.ecc.steps; > > > + int i , j, stat = 0; > > > + int eccsize, eccflag, size; > > > + struct elm_errorvec err_vec[ERROR_VECTOR_MAX]; > > > + u_char *ecc_vec = calc_ecc; > > > + enum bch_ecc type; > > > + bool is_error_reported = false; > > > + > > > + /* initialize elm error vector to zero */ > > > + memset(err_vec, 0, sizeof(err_vec)); > > > + if (info->nand.ecc.strength == BCH8_MAX_ERROR) { > > > + size = BCH8_SIZE; > > > + eccsize = BCH8_ECC_OOB_BYTES; > > > + type = BCH8_ECC; > > > + } else { > > > + size = BCH4_SIZE; > > > + eccsize = BCH4_SIZE; > > > + type = BCH4_ECC; > > > + } > > > + > > > + for (i = 0; i < eccsteps ; i++) { > > > + eccflag = 0; /* initialize eccflag */ > > > + > > > + for (j = 0; (j < eccsize); j++) { > > > + if (read_ecc[j] != 0xFF) { > > > + eccflag = 1; /* data area is flashed */ > > > > Just a reminder: this way of checking if a page has been programmed is not robust to bitflips, > > so you may get into trouble with UBIFS on a fairly recent device. Sorry I missed this point. Here we were checking data in spare area (only in ecc layout 14*4 for BCH8) is 0xFF. If all data in spare area is 0xFF, conclude that the page is erased & no need of error correction. In case of bit flip present in spare area, page will be reported as uncorrectable. But I am not understand understand " trouble with UBIFS on a fairly recent device". Can you little elaborativ Thanks Avinash -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/