From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755285Ab2HOPEW (ORCPT ); Wed, 15 Aug 2012 11:04:22 -0400 Received: from mga11.intel.com ([192.55.52.93]:23415 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752064Ab2HOPES (ORCPT ); Wed, 15 Aug 2012 11:04:18 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.77,773,1336374000"; d="asc'?scan'208";a="208815731" Message-ID: <1345043331.3393.151.camel@sauron.fi.intel.com> Subject: Re: [PATCH 3/4] UBI: use the whole MTD device size to get bad_peb_limit From: Artem Bityutskiy Reply-To: dedekind1@gmail.com To: Richard Genoud , Shmulik Ladkani Cc: David Woodhouse , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Date: Wed, 15 Aug 2012 18:08:51 +0300 In-Reply-To: <1341937423-16516-4-git-send-email-richard.genoud@gmail.com> References: <1341937423-16516-1-git-send-email-richard.genoud@gmail.com> <1341937423-16516-4-git-send-email-richard.genoud@gmail.com> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-cV0IXn8Tq7/1j6+HeM2t" X-Mailer: Evolution 3.2.3 (3.2.3-3.fc16) Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-cV0IXn8Tq7/1j6+HeM2t Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2012-07-10 at 18:23 +0200, Richard Genoud wrote: > + /* we are using here the whole MTD device size and not > + * the MTD partition size because the maximum number of > + * bad blocks is a percentage of the whole device and > + * the bad blocks are not fairly disposed on a flash > + * device > + */ Would you please use proper kernel-style comments instead, to be consistent with the rest of the UBI code? I've amended this one, but wanted to note for future. I've re-based your patch against the latest UBI. I've also tried to improve the Kconfig help message as well. Below is the patch I ended up with. =46rom cb14c6c5455443cbe960a36e77b3fcd0e5bc7152 Mon Sep 17 00:00:00 2001 From: Richard Genoud Date: Tue, 10 Jul 2012 18:23:41 +0200 Subject: [PATCH 2/2] UBI: use the whole MTD device size to get bad_peb_limi= t On NAND flash devices, UBI reserves some physical erase blocks (PEB) for bad block handling. Today, the number of reserved PEB can only be set as a percentage of the total number of PEB in each MTD partition. For example, f= or a NAND flash with 128KiB PEB, 2 MTD partition of 20MiB (mtd0) and 100MiB (mtd= 1) and 2% reserved PEB: - the UBI device on mtd0 will have 2 PEB reserved - the UBI device on mtd1 will have 16 PEB reserved The problem with this behaviour is that NAND flash manufacturers give a minimum number of valid block (NVB) during the endurance life of the device, e.g.: Parameter Symbol Min Max Unit Notes -------------------------------------------------------------- Valid block number NVB 1004 1024 Blocks 1 Note: 1. Invalid blocks are block that contain one or more bad bits beyond ECC. The device may contain bad blocks upon shipment. Additional bad blocks may develop over time; however, the total number of available blocks will not drop below NVB during the endurance life of the device. =46rom this number we can deduce the maximum number of bad PEB that a device = will contain during its endurance life: a 128MiB NAND flash (1024 PEB) will not = have less than 20 bad blocks during the flash endurance life. But the manufacturer doesn't tell where those bad block will appear. He doe= sn't say either if they will be equally disposed on the whole device (and I'm pr= etty sure they won't). So, according to the datasheets, we should reserve the maximum number of bad PEB for each UBI device (worst case scenario: 20 bad blocks appears on the smallest MTD partition). So this patch make UBI use the whole MTD device size to calculate the maxim= um bad expected eraseblocks. The Kconfig option is in per1024 blocks, thus it can have a default value o= f 20 which is *very* common for NAND devices. Signed-off-by: Richard Genoud Signed-off-by: Artem Bityutskiy --- drivers/mtd/ubi/Kconfig | 27 +++++++++++++++++++++------ drivers/mtd/ubi/build.c | 21 ++++++++++++++++++--- 2 files changed, 39 insertions(+), 9 deletions(-) diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig index b2f4f0f..98bda6c 100644 --- a/drivers/mtd/ubi/Kconfig +++ b/drivers/mtd/ubi/Kconfig @@ -28,14 +28,29 @@ config MTD_UBI_WL_THRESHOLD to 128 or 256, although it does not have to be power of 2). =20 config MTD_UBI_BEB_LIMIT - int "Percentage of maximum expected bad eraseblocks" - default 2 - range 0 25 + int "Maximum expected bad eraseblock count per 1024 eraseblocks" + default 20 + range 2 256 help This option specifies the maximum bad physical eraseblocks UBI - expects on the UBI device (percents of total number of physical - eraseblocks on this MTD partition). If the underlying flash does not - admit of bad eraseblocks (e.g. NOR flash), this value is ignored. + expects on the MTD device (per 1024 eraseblocks). If the underlying + flash does not admit of bad eraseblocks (e.g. NOR flash), this value + is ignored. + + NAND datasheets often specify the minimum and maximum NVM (Number of + Valid Blocks) for the flashes' endurance lifetime. The maximum + expected bad eraseblocks per 1024 eraseblocks then can be calculated + as "1024 * (1 - MinNVB / MaxNVB)", which gives 20 for most NANDs + (MaxNVB is basically the total count of eraseblocks on the chip). + + To put it differently, if this value is 20, UBI will try to reserve + about 1.9% of physical eraseblocks for bad blocks handling. And that + will be 1.9% of eraseblocks on the entire NAND chip, not just the MTD + partition UBI attaches. This means that if you have, say, if a NAND + flash chip admits maximum 40 bad eraseblocks, and it is split on two + MTD partitions of the same size, UBI will reserve 40 eraseblocks when + attaching a partition. + Leave the default value if unsure. =20 config MTD_UBI_GLUEBI diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c index 7b6b5f9..9fd8d86 100644 --- a/drivers/mtd/ubi/build.c +++ b/drivers/mtd/ubi/build.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include #include @@ -610,11 +611,25 @@ static int io_init(struct ubi_device *ubi) if (mtd_can_have_bb(ubi->mtd)) { ubi->bad_allowed =3D 1; if (CONFIG_MTD_UBI_BEB_LIMIT > 0) { - int percent =3D CONFIG_MTD_UBI_BEB_LIMIT; - int limit =3D mult_frac(ubi->peb_count, percent, 100); + int per1024 =3D CONFIG_MTD_UBI_BEB_LIMIT; + int limit, device_pebs; + uint64_t device_size; + + /* + * Here we are using size of the entire flash chip and + * not just the MTD partition size because the maximum + * number of bad eraseblocks is a percentage of the + * whole device and bad eraseblocks are not fairly + * distributed over the flash chip. So the worst case + * is that all the bad eraseblocks of the chip are in + * the MTD partition we are attaching (ubi->mtd). + */ + device_size =3D mtd_get_device_size(ubi->mtd); + device_pebs =3D mtd_div_by_eb(device_size, ubi->mtd); + limit =3D mult_frac(device_pebs, per1024, 1024); =20 /* Round it up */ - if (mult_frac(limit, 100, percent) < ubi->peb_count) + if (mult_frac(limit, 1024, per1024) < ubi->peb_count) limit +=3D 1; ubi->bad_peb_limit =3D limit; } --=20 1.7.10.4 --=20 Best Regards, Artem Bityutskiy --=-cV0IXn8Tq7/1j6+HeM2t Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAABAgAGBQJQK7uDAAoJECmIfjd9wqK0ik4QAKWloDWbFBvb37HHjRYUlezV pW7zWA6L6+jst4EHB7hFOqxGMzrxFLV8n08t3m7kw72+lvSoCL/Wnu62869ghNIg FUeZAFh0wGZlDxOmAiqxD9N5m51A6WMs7P4/5AyuaqU4CZzuGHIZv/zuT9XAU0k7 679xscPaCv9smHaMO32ftLuYy7N8sweIJq3hSd/VPSOPd7Q1HgSsOnbiiFDJM+Kx qz/kmz9xmREkX3QvDnzKktP8IgkNulaf707UvPLBRdAktA4IuWo6RO7ZI0L6MATN RWn9kjxjoRO4EGfQKB4BbQfEdTTHEyF6W5jqgdMD/yiN73gbD+psp+iGyQL96LCt h0IwqlzesASUikC69DXGYPPJISL6whAvkx1BhDiLywimc9mk/6r9oGllAtx9gYvR YMpMF0LL0iWHY1UHAeX8aAQ+Ra6uhdH4IcIyJRI821zGpbsrUsIzlq8/+57nPH4e SWXHWpWyUMYBiBBe32loABZc344PAkvtTWd064X6zAJk47WplhLYrCzID0zK1irC Dka4huJ3EU23xal74VQKM11QChPB8S2jiHpiL57G0a3lqvQjbW8HiiVEHbPVw8tF 8opC+4xyM6qHHCKbn9Kb1j+wkrsTJ3u+mYeCihRxj44Hod+zjRgZiCCYKZ0MuORu 9FkiSyuEdKVebjdozA8g =lOS6 -----END PGP SIGNATURE----- --=-cV0IXn8Tq7/1j6+HeM2t--