[PATCH 0/3] [PATCH 0/3] mtd: nand: omap: Use Software ECC by default

[PATCH 0/3] [PATCH 0/3] mtd: nand: omap: Use Software ECC by default

[Roger Quadros]

Hi,

In Linux v3.12 and earlier some boards [1] used Software based ECC as
the NAND ECC scheme. In 3.13 commit c66d039197e4 changed that to
Hardware ECC using ROM code ECC layout. This will cause NAND filesystems
created in 3.12 and earlier to be unreadable in v3.13 and later till
they are erased and re-created.

This series fixes this issue by using Software ECC as the default ECC
scheme for the affected boards.

Tested on omap3beagle.

[1] - Affected boards
-omap3beagle
-omap3touchbook
-overo
-am3517crane
-devkit8000
-ldp
-3430sdp

cheers,
-roger

---
Roger Quadros (3):
  mtd: nand: omap: Revert to using software ECC by default
  ARM: OMAP2+: GPMC: Support Software ECC scheme via DT
  ARM: dts: omap3430-sdp: Revert to using software ECC for NAND

 Documentation/devicetree/bindings/mtd/gpmc-nand.txt |  2 +-
 arch/arm/boot/dts/omap3430-sdp.dts                  |  2 +-
 arch/arm/mach-omap2/board-flash.c                   |  2 +-
 arch/arm/mach-omap2/gpmc-nand.c                     |  3 ++-
 arch/arm/mach-omap2/gpmc.c                          |  7 +++++--
 drivers/mtd/nand/omap2.c                            | 14 +++++++++++---
 include/linux/platform_data/mtd-nand-omap2.h        | 13 +++++++++++--
 7 files changed, 32 insertions(+), 11 deletions(-)

-- 
1.8.3.2

[PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Roger Quadros]

For v3.12 and prior, 1-bit Hamming code ECC via software was the
default choice. Commit c66d039197e4 in v3.13 changed the behaviour
to use 1-bit Hamming code via Hardware using a different ECC layout
i.e. (ROM code layout) than what is used by software ECC.

This ECC layout change causes NAND filesystems created in v3.12
and prior to be unusable in v3.13 and later. So revert back to
using software ECC by default if an ECC scheme is not explicitely
specified.

This defect can be observed on the following boards during legacy boot

-omap3beagle
-omap3touchbook
-overo
-am3517crane
-devkit8000
-ldp
-3430sdp

Signed-off-by: Roger Quadros <rogerq@ti.com>
---
 arch/arm/mach-omap2/board-flash.c            |  2 +-
 arch/arm/mach-omap2/gpmc-nand.c              |  3 ++-
 drivers/mtd/nand/omap2.c                     | 14 +++++++++++---
 include/linux/platform_data/mtd-nand-omap2.h | 13 +++++++++++--
 4 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/arch/arm/mach-omap2/board-flash.c b/arch/arm/mach-omap2/board-flash.c
index e87f2a8..2d245c2 100644
--- a/arch/arm/mach-omap2/board-flash.c
+++ b/arch/arm/mach-omap2/board-flash.c
@@ -142,7 +142,7 @@ __init board_nand_init(struct mtd_partition *nand_parts, u8 nr_parts, u8 cs,
 	board_nand_data.nr_parts	= nr_parts;
 	board_nand_data.devsize		= nand_type;
 
-	board_nand_data.ecc_opt = OMAP_ECC_HAM1_CODE_HW;
+	board_nand_data.ecc_opt = OMAP_ECC_HAM1_CODE_SW;
 	gpmc_nand_init(&board_nand_data, gpmc_t);
 }
 #endif /* CONFIG_MTD_NAND_OMAP2 || CONFIG_MTD_NAND_OMAP2_MODULE */
diff --git a/arch/arm/mach-omap2/gpmc-nand.c b/arch/arm/mach-omap2/gpmc-nand.c
index 93914d2..03b6f95 100644
--- a/arch/arm/mach-omap2/gpmc-nand.c
+++ b/arch/arm/mach-omap2/gpmc-nand.c
@@ -68,7 +68,8 @@ static bool gpmc_hwecc_bch_capable(enum omap_ecc ecc_opt)
 		return 0;
 
 	/* legacy platforms support only HAM1 (1-bit Hamming) ECC scheme */
-	if (ecc_opt == OMAP_ECC_HAM1_CODE_HW)
+	if (ecc_opt == OMAP_ECC_HAM1_CODE_HW ||
+	    ecc_opt == OMAP_ECC_HAM1_CODE_SW)
 		return 1;
 	else
 		return 0;
diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
index f0ed92e..4dd6178 100644
--- a/drivers/mtd/nand/omap2.c
+++ b/drivers/mtd/nand/omap2.c
@@ -1794,9 +1794,12 @@ static int omap_nand_probe(struct platform_device *pdev)
 	}
 
 	/* populate MTD interface based on ECC scheme */
-	nand_chip->ecc.layout	= &omap_oobinfo;
 	ecclayout		= &omap_oobinfo;
 	switch (info->ecc_opt) {
+	case OMAP_ECC_HAM1_CODE_SW:
+		nand_chip->ecc.mode = NAND_ECC_SOFT;
+		break;
+
 	case OMAP_ECC_HAM1_CODE_HW:
 		pr_info("nand: using OMAP_ECC_HAM1_CODE_HW\n");
 		nand_chip->ecc.mode             = NAND_ECC_HW;
@@ -1848,7 +1851,7 @@ static int omap_nand_probe(struct platform_device *pdev)
 		nand_chip->ecc.priv		= nand_bch_init(mtd,
 							nand_chip->ecc.size,
 							nand_chip->ecc.bytes,
-							&nand_chip->ecc.layout);
+							&ecclayout);
 		if (!nand_chip->ecc.priv) {
 			pr_err("nand: error: unable to use s/w BCH library\n");
 			err = -EINVAL;
@@ -1923,7 +1926,7 @@ static int omap_nand_probe(struct platform_device *pdev)
 		nand_chip->ecc.priv		= nand_bch_init(mtd,
 							nand_chip->ecc.size,
 							nand_chip->ecc.bytes,
-							&nand_chip->ecc.layout);
+							&ecclayout);
 		if (!nand_chip->ecc.priv) {
 			pr_err("nand: error: unable to use s/w BCH library\n");
 			err = -EINVAL;
@@ -2012,6 +2015,9 @@ static int omap_nand_probe(struct platform_device *pdev)
 		goto return_error;
 	}
 
+	if (info->ecc_opt == OMAP_ECC_HAM1_CODE_SW)
+		goto scan_tail;
+
 	/* all OOB bytes from oobfree->offset till end off OOB are free */
 	ecclayout->oobfree->length = mtd->oobsize - ecclayout->oobfree->offset;
 	/* check if NAND device's OOB is enough to store ECC signatures */
@@ -2021,7 +2027,9 @@ static int omap_nand_probe(struct platform_device *pdev)
 		err = -EINVAL;
 		goto return_error;
 	}
+	nand_chip->ecc.layout = ecclayout;
 
+scan_tail:
 	/* second phase scan */
 	if (nand_scan_tail(mtd)) {
 		err = -ENXIO;
diff --git a/include/linux/platform_data/mtd-nand-omap2.h b/include/linux/platform_data/mtd-nand-omap2.h
index 660c029..16ec262 100644
--- a/include/linux/platform_data/mtd-nand-omap2.h
+++ b/include/linux/platform_data/mtd-nand-omap2.h
@@ -21,8 +21,17 @@ enum nand_io {
 };
 
 enum omap_ecc {
-	/* 1-bit  ECC calculation by GPMC, Error detection by Software */
-	OMAP_ECC_HAM1_CODE_HW = 0,
+	/*
+	 * 1-bit ECC: calculation and correction by SW
+	 * ECC stored at end of spare area
+	 */
+	OMAP_ECC_HAM1_CODE_SW = 0,
+
+	/*
+	 * 1-bit ECC: calculation by GPMC, Error detection by Software
+	 * ECC layout compatible with ROM code layout
+	 */
+	OMAP_ECC_HAM1_CODE_HW,
 	/* 4-bit  ECC calculation by GPMC, Error detection by Software */
 	OMAP_ECC_BCH4_CODE_HW_DETECTION_SW,
 	/* 4-bit  ECC calculation by GPMC, Error detection by ELM */
-- 
1.8.3.2

Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Grazvydas Ignotas]

On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
> For v3.12 and prior, 1-bit Hamming code ECC via software was the
> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
> to use 1-bit Hamming code via Hardware using a different ECC layout
> i.e. (ROM code layout) than what is used by software ECC.
>
> This ECC layout change causes NAND filesystems created in v3.12
> and prior to be unusable in v3.13 and later. So revert back to
> using software ECC by default if an ECC scheme is not explicitely
> specified.
>
> This defect can be observed on the following boards during legacy boot
>
> -omap3beagle
> -omap3touchbook
> -overo
> -am3517crane
> -devkit8000
> -ldp
> -3430sdp

omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
booting mainline (I think it was 3.14) with rootfs on NAND, and while
it did boot and reached a shell, there were lots of ubifs errors, fs
got corrupted and I lost all my data. I used to be able to boot
mainline this way fine sometime ~3.8 release. It's interesting that
3.14 was able to read the data, even with wrong ecc setup.

Do you think it's safe again to boot ubifs created on 3.2 after
applying this series?

-- 
Gražvydas

Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[pekon]

Hi Roger,

On Tuesday 05 August 2014 09:45 PM, Grazvydas Ignotas wrote:
> On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
>> For v3.12 and prior, 1-bit Hamming code ECC via software was the
>> default choice. Commit c66d039197e4 in v3.13 changed the behavior
>> to use 1-bit Hamming code via Hardware using a different ECC layout
>> i.e. (ROM code layout) than what is used by software ECC.
>>
As per OMAP3 TRM [1], the NAND ECC layout required for
NAND boot is same as that of OMAP_ECC_HAM1_CODE_HW. So
above mentioned 'commit c66d039197e4' does not break
backward compatibility as far as NAND boot is concerned.

AFAIK, all users on OMAP3 used HAM1_HW which is same
as HAM1 today. So unless we have a real OMAP3 user who
(1) had created file-system using HAM1_SW &&
(2) now wants to migrate to new kernel, I don't think
its wise to re-introduce HAM1_SW4 ECC schemes.

Instead we are trying to push OMAP3 users to migrate to
BCH4_SW (supported by ROM) or BCH8_SW ECC schemes.

Please understand
commit c66d039197e42af8867e5d0d9b904daf0fb9e6bc
was part of larger series to clean-up NAND driver and
remove obsolete or redundant code. So this was
intentional change.



>> This ECC layout change causes NAND filesystems created in v3.12
>> and prior to be unusable in v3.13 and later. So revert back to
>> using software ECC by default if an ECC scheme is not explicitely
>> specified.
>>
>> This defect can be observed on the following boards during legacy 
>> boot
>>
>> -omap3beagle
>> -omap3touchbook
>> -overo
>> -am3517crane
>> -devkit8000
>> -ldp
>> -3430sdp
>
> omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
> booting mainline (I think it was 3.14) with rootfs on NAND, and while
> it did boot and reached a shell, there were lots of ubifs errors, fs
> got corrupted and I lost all my data. I used to be able to boot
> mainline this way fine sometime ~3.8 release. It's interesting that
> 3.14 was able to read the data, even with wrong ecc setup.
>
> Do you think it's safe again to boot ubifs created on 3.2 after
> applying this series?
>
Are you sure you are using "sw" ECC scheme ?
Can you please share the ecc-layout of the NAND page, because
as per [1] you should not be able to Boot from NAND then.

IIRC..
- ECC layout of HAM1_SW has ECC bytes towards end of OOB-section.
- ECC layout of HAM1_HW has ECC bytes towards staring of OOB section.


with regards, pekon


[1] http://www.ti.com/product/omap3530
http://www.ti.com/lit/pdf/spruf98  (Revision Y)
Chapter 25: Initialization
Section: 25.4.7 Memory Booting
	Sub-Section: NAND
	Figure 25-19. ECC Locations in NAND Spare Areas


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Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Roger Quadros]

Hi Pekon,

On 08/05/2014 11:30 PM, pekon@pek-sem.com wrote:
> Hi Roger,
> 
> On Tuesday 05 August 2014 09:45 PM, Grazvydas Ignotas wrote:
>> On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
>>> For v3.12 and prior, 1-bit Hamming code ECC via software was the
>>> default choice. Commit c66d039197e4 in v3.13 changed the behavior
>>> to use 1-bit Hamming code via Hardware using a different ECC layout
>>> i.e. (ROM code layout) than what is used by software ECC.
>>>
> As per OMAP3 TRM [1], the NAND ECC layout required for
> NAND boot is same as that of OMAP_ECC_HAM1_CODE_HW. So

No. The layout is different. What I mean by OMAP_ECC_HAM1_CODE_SW is what earlier was OMAP_ECC_HAMMING_CODE_DEFAULT.
It sets nand.ecc.mode to NAND_ECC_SOFT and doesn't use OMAP ROM code layout.

> above mentioned 'commit c66d039197e4' does not break
> backward compatibility as far as NAND boot is concerned.

It does. Grazvydas has reported it and I have observed it on omap3beagle with legacy boot when switching from v3.12 to v3.13 and later.

> 
> AFAIK, all users on OMAP3 used HAM1_HW which is same
> as HAM1 today. So unless we have a real OMAP3 user who
> (1) had created file-system using HAM1_SW &&
> (2) now wants to migrate to new kernel, I don't think
> its wise to re-introduce HAM1_SW4 ECC schemes.

many boards using legacy boot don't explicitly set ecc_opt parameter of nand_platform_data. So that is set to 0.
commit c66d039197e4 changed the meaning from default ECC layout to OMAP ROM code layout and hence the regressions.

> 
> Instead we are trying to push OMAP3 users to migrate to
> BCH4_SW (supported by ROM) or BCH8_SW ECC schemes.
> 
> Please understand
> commit c66d039197e42af8867e5d0d9b904daf0fb9e6bc
> was part of larger series to clean-up NAND driver and
> remove obsolete or redundant code. So this was
> intentional change.
> 
> 
> 
>>> This ECC layout change causes NAND filesystems created in v3.12
>>> and prior to be unusable in v3.13 and later. So revert back to
>>> using software ECC by default if an ECC scheme is not explicitely
>>> specified.
>>>
>>> This defect can be observed on the following boards during legacy boot
>>>
>>> -omap3beagle
>>> -omap3touchbook
>>> -overo
>>> -am3517crane
>>> -devkit8000
>>> -ldp
>>> -3430sdp
>>
>> omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
>> booting mainline (I think it was 3.14) with rootfs on NAND, and while
>> it did boot and reached a shell, there were lots of ubifs errors, fs
>> got corrupted and I lost all my data. I used to be able to boot
>> mainline this way fine sometime ~3.8 release. It's interesting that
>> 3.14 was able to read the data, even with wrong ecc setup.
>>
>> Do you think it's safe again to boot ubifs created on 3.2 after
>> applying this series?
>>
> Are you sure you are using "sw" ECC scheme ?
> Can you please share the ecc-layout of the NAND page, because

ecc-layout for software scheme depends on oob size.
http://lxr.free-electrons.com/source/drivers/mtd/nand/nand_base.c#L53

> as per [1] you should not be able to Boot from NAND then.

Bootpartition and filesystem partition are different. Boot partition needs to be compatible with OMAP ROM code layout but root filesystem doesn't need to be. I agree that it is best to use the same for but if boards have been using a different layout for filesystem then we need to maintain backward compatibility.

> 
> IIRC..
> - ECC layout of HAM1_SW has ECC bytes towards end of OOB-section.
> - ECC layout of HAM1_HW has ECC bytes towards staring of OOB section.

The main difference between sw layout and ROM code layout is
- sw layout always starts at offset 0
- rom layout starts at 1 for x8 device and 2 for x16 device.

cheers,
-roger

Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Roger Quadros]

Hi Gražvydas,

On 08/05/2014 07:15 PM, Grazvydas Ignotas wrote:
> On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
>> For v3.12 and prior, 1-bit Hamming code ECC via software was the
>> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
>> to use 1-bit Hamming code via Hardware using a different ECC layout
>> i.e. (ROM code layout) than what is used by software ECC.
>>
>> This ECC layout change causes NAND filesystems created in v3.12
>> and prior to be unusable in v3.13 and later. So revert back to
>> using software ECC by default if an ECC scheme is not explicitely
>> specified.
>>
>> This defect can be observed on the following boards during legacy boot
>>
>> -omap3beagle
>> -omap3touchbook
>> -overo
>> -am3517crane
>> -devkit8000
>> -ldp
>> -3430sdp
> 
> omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
> booting mainline (I think it was 3.14) with rootfs on NAND, and while
> it did boot and reached a shell, there were lots of ubifs errors, fs
> got corrupted and I lost all my data. I used to be able to boot
> mainline this way fine sometime ~3.8 release. It's interesting that
> 3.14 was able to read the data, even with wrong ecc setup.

This is due to another bug introduced in 3.7 by commit 65b97cf6b8deca3ad7a3e00e8316bb89617190fb.
Because of that bug (i.e. inverted CS_MASK in omap_calculate_ecc), omap_calculate_ecc() always fails with -EINVAL and calculated ECC bytes are always 0. I'll be sending a patch to fix that as well. But that will only affect the cases where OMAP_ECC_HAM1_CODE_HW is used which happened for pandora from 3.13 onwards.

> 
> Do you think it's safe again to boot ubifs created on 3.2 after
> applying this series?
> 

Yes. If you boot pandora using legacy boot (non DT method), it passes 0 for .ecc_opt in pandora_nand_data. This used to mean OMAP_ECC_HAMMING_CODE_DEFAULT which is software ecc. i.e. NAND_ECC_SOFT with default ECC layout. Until the above mentioned commits changed the meaning. We now call that option OMAP_ECC_HAM1_CODE_SW.

Please let me know if it works for you. Thanks.

cheers,
-roger

Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Grazvydas Ignotas]

On Wed, Aug 6, 2014 at 11:02 AM, Roger Quadros <rogerq@ti.com> wrote:
> Hi Gražvydas,
>
> On 08/05/2014 07:15 PM, Grazvydas Ignotas wrote:
>> On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
>>> For v3.12 and prior, 1-bit Hamming code ECC via software was the
>>> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
>>> to use 1-bit Hamming code via Hardware using a different ECC layout
>>> i.e. (ROM code layout) than what is used by software ECC.
>>>
>>> This ECC layout change causes NAND filesystems created in v3.12
>>> and prior to be unusable in v3.13 and later. So revert back to
>>> using software ECC by default if an ECC scheme is not explicitely
>>> specified.
>>>
>>> This defect can be observed on the following boards during legacy boot
>>>
>>> -omap3beagle
>>> -omap3touchbook
>>> -overo
>>> -am3517crane
>>> -devkit8000
>>> -ldp
>>> -3430sdp
>>
>> omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
>> booting mainline (I think it was 3.14) with rootfs on NAND, and while
>> it did boot and reached a shell, there were lots of ubifs errors, fs
>> got corrupted and I lost all my data. I used to be able to boot
>> mainline this way fine sometime ~3.8 release. It's interesting that
>> 3.14 was able to read the data, even with wrong ecc setup.
>
> This is due to another bug introduced in 3.7 by commit 65b97cf6b8deca3ad7a3e00e8316bb89617190fb.
> Because of that bug (i.e. inverted CS_MASK in omap_calculate_ecc), omap_calculate_ecc() always fails with -EINVAL and calculated ECC bytes are always 0. I'll be sending a patch to fix that as well. But that will only affect the cases where OMAP_ECC_HAM1_CODE_HW is used which happened for pandora from 3.13 onwards.
>
>>
>> Do you think it's safe again to boot ubifs created on 3.2 after
>> applying this series?
>>
>
> Yes. If you boot pandora using legacy boot (non DT method), it passes 0 for .ecc_opt in pandora_nand_data. This used to mean OMAP_ECC_HAMMING_CODE_DEFAULT which is software ecc. i.e. NAND_ECC_SOFT with default ECC layout. Until the above mentioned commits changed the meaning. We now call that option OMAP_ECC_HAM1_CODE_SW.
>
> Please let me know if it works for you. Thanks.

Yes it does, thank you.
Tested-by: Grazvydas Ignotas <notasas@gmail.com>

Found something new in dmesg though:
[    1.542755] nand: device found, Manufacturer ID: 0x2c, Chip ID: 0xbc
[    1.549621] nand: Micron MT29F4G16ABBDA3W
[    1.553894] nand: 512MiB, SLC, page size: 2048, OOB size: 64
[    1.560058] nand: WARNING: omap2-nand.0: the ECC used on your
system is too weak compared to the one required by the NAND chip

Do you think it's best to migrate to different ECC scheme? It would be
better to avoid that so that users can freely change kernels and the
bootloader wouldn't have to be changed..

-- 
Gražvydas

Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Roger Quadros]

On 08/07/2014 01:55 AM, Grazvydas Ignotas wrote:
> On Wed, Aug 6, 2014 at 11:02 AM, Roger Quadros <rogerq@ti.com> wrote:
>> Hi Gražvydas,
>>
>> On 08/05/2014 07:15 PM, Grazvydas Ignotas wrote:
>>> On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
>>>> For v3.12 and prior, 1-bit Hamming code ECC via software was the
>>>> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
>>>> to use 1-bit Hamming code via Hardware using a different ECC layout
>>>> i.e. (ROM code layout) than what is used by software ECC.
>>>>
>>>> This ECC layout change causes NAND filesystems created in v3.12
>>>> and prior to be unusable in v3.13 and later. So revert back to
>>>> using software ECC by default if an ECC scheme is not explicitely
>>>> specified.
>>>>
>>>> This defect can be observed on the following boards during legacy boot
>>>>
>>>> -omap3beagle
>>>> -omap3touchbook
>>>> -overo
>>>> -am3517crane
>>>> -devkit8000
>>>> -ldp
>>>> -3430sdp
>>>
>>> omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
>>> booting mainline (I think it was 3.14) with rootfs on NAND, and while
>>> it did boot and reached a shell, there were lots of ubifs errors, fs
>>> got corrupted and I lost all my data. I used to be able to boot
>>> mainline this way fine sometime ~3.8 release. It's interesting that
>>> 3.14 was able to read the data, even with wrong ecc setup.
>>
>> This is due to another bug introduced in 3.7 by commit 65b97cf6b8deca3ad7a3e00e8316bb89617190fb.
>> Because of that bug (i.e. inverted CS_MASK in omap_calculate_ecc), omap_calculate_ecc() always fails with -EINVAL and calculated ECC bytes are always 0. I'll be sending a patch to fix that as well. But that will only affect the cases where OMAP_ECC_HAM1_CODE_HW is used which happened for pandora from 3.13 onwards.
>>
>>>
>>> Do you think it's safe again to boot ubifs created on 3.2 after
>>> applying this series?
>>>
>>
>> Yes. If you boot pandora using legacy boot (non DT method), it passes 0 for .ecc_opt in pandora_nand_data. This used to mean OMAP_ECC_HAMMING_CODE_DEFAULT which is software ecc. i.e. NAND_ECC_SOFT with default ECC layout. Until the above mentioned commits changed the meaning. We now call that option OMAP_ECC_HAM1_CODE_SW.
>>
>> Please let me know if it works for you. Thanks.
> 
> Yes it does, thank you.
> Tested-by: Grazvydas Ignotas <notasas@gmail.com>
> 
> Found something new in dmesg though:
> [    1.542755] nand: device found, Manufacturer ID: 0x2c, Chip ID: 0xbc
> [    1.549621] nand: Micron MT29F4G16ABBDA3W
> [    1.553894] nand: 512MiB, SLC, page size: 2048, OOB size: 64
> [    1.560058] nand: WARNING: omap2-nand.0: the ECC used on your
> system is too weak compared to the one required by the NAND chip
> 
> Do you think it's best to migrate to different ECC scheme? It would be
> better to avoid that so that users can freely change kernels and the
> bootloader wouldn't have to be changed..
> 
I'm not sure why these boards were using Software ECC scheme in the first place.
So moving to a better ECC scheme should be considered with a warning that backward
compatibility will be broken.

There is a limitation with the OMAP3 ROM code loader. So if you want uniform ECC scheme
for MLO, u-boot and kernel partitions then we are limited to Hamming code for SLC NAND with
512B, 2KB and 4KB pages.

For MLC NAND, the ROM code uses a proprietary layout using checksum and BCH and I'm not very sure
if this is compatible with the newer OMAP platforms and AM33xx platforms.

For details see OMAP35x TRM. (spruf98y.pdf)
http://www.ti.com/lit/ug/spruf98y/spruf98y.pdf
sections
25.4.7.4.2 SLC NAND Read Sector Procedure
25.4.7.4.3 MLC NAND Read Sector Procedure

cheers,
-roger

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Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

[Tony Lindgren]

* Grazvydas Ignotas <notasas@gmail.com> [140806 15:57]:
> On Wed, Aug 6, 2014 at 11:02 AM, Roger Quadros <rogerq@ti.com> wrote:
> > Hi Gražvydas,
> >
> > On 08/05/2014 07:15 PM, Grazvydas Ignotas wrote:
> >> On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
> >>> For v3.12 and prior, 1-bit Hamming code ECC via software was the
> >>> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
> >>> to use 1-bit Hamming code via Hardware using a different ECC layout
> >>> i.e. (ROM code layout) than what is used by software ECC.
> >>>
> >>> This ECC layout change causes NAND filesystems created in v3.12
> >>> and prior to be unusable in v3.13 and later. So revert back to
> >>> using software ECC by default if an ECC scheme is not explicitely
> >>> specified.
> >>>
> >>> This defect can be observed on the following boards during legacy boot
> >>>
> >>> -omap3beagle
> >>> -omap3touchbook
> >>> -overo
> >>> -am3517crane
> >>> -devkit8000
> >>> -ldp
> >>> -3430sdp
> >>
> >> omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
> >> booting mainline (I think it was 3.14) with rootfs on NAND, and while
> >> it did boot and reached a shell, there were lots of ubifs errors, fs
> >> got corrupted and I lost all my data. I used to be able to boot
> >> mainline this way fine sometime ~3.8 release. It's interesting that
> >> 3.14 was able to read the data, even with wrong ecc setup.
> >
> > This is due to another bug introduced in 3.7 by commit 65b97cf6b8deca3ad7a3e00e8316bb89617190fb.
> > Because of that bug (i.e. inverted CS_MASK in omap_calculate_ecc), omap_calculate_ecc() always fails with -EINVAL and calculated ECC bytes are always 0. I'll be sending a patch to fix that as well. But that will only affect the cases where OMAP_ECC_HAM1_CODE_HW is used which happened for pandora from 3.13 onwards.
> >
> >>
> >> Do you think it's safe again to boot ubifs created on 3.2 after
> >> applying this series?
> >>
> >
> > Yes. If you boot pandora using legacy boot (non DT method), it passes 0 for .ecc_opt in pandora_nand_data. This used to mean OMAP_ECC_HAMMING_CODE_DEFAULT which is software ecc. i.e. NAND_ECC_SOFT with default ECC layout. Until the above mentioned commits changed the meaning. We now call that option OMAP_ECC_HAM1_CODE_SW.
> >
> > Please let me know if it works for you. Thanks.
> 
> Yes it does, thank you.
> Tested-by: Grazvydas Ignotas <notasas@gmail.com>

OK thanks applying the whole series into omap-for-v3.17/fixes.

Tony
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[PATCH 2/3] ARM: OMAP2+: GPMC: Support Software ECC scheme via DT

[Roger Quadros]

For v3.14 and prior, 1-bit Hamming code ECC via software was the
default choice for some boards e.g. 3430sdp.
Commit ac65caf514ec in v3.15 changed the behaviour
to use 1-bit Hamming code via Hardware using a different ECC layout
i.e. (ROM code layout) than what is used by software ECC.

This ECC layout change causes NAND filesystems created in v3.14
and prior to be unusable in v3.15 and later. So don't mark "sw" scheme
as deperecated and support it.

Signed-off-by: Roger Quadros <rogerq@ti.com>
---
 Documentation/devicetree/bindings/mtd/gpmc-nand.txt | 2 +-
 arch/arm/mach-omap2/gpmc.c                          | 7 +++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
index 65f4f7c..ee654e9 100644
--- a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
+++ b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt
@@ -22,7 +22,7 @@ Optional properties:
 				width of 8 is assumed.
 
  - ti,nand-ecc-opt:		A string setting the ECC layout to use. One of:
-		"sw"		<deprecated> use "ham1" instead
+		"sw"		1-bit Hamming ecc code via software
 		"hw"		<deprecated> use "ham1" instead
 		"hw-romcode"	<deprecated> use "ham1" instead
 		"ham1"		1-bit Hamming ecc code
diff --git a/arch/arm/mach-omap2/gpmc.c b/arch/arm/mach-omap2/gpmc.c
index 8bc1338..9f42d54 100644
--- a/arch/arm/mach-omap2/gpmc.c
+++ b/arch/arm/mach-omap2/gpmc.c
@@ -1403,8 +1403,11 @@ static int gpmc_probe_nand_child(struct platform_device *pdev,
 		pr_err("%s: ti,nand-ecc-opt not found\n", __func__);
 		return -ENODEV;
 	}
-	if (!strcmp(s, "ham1") || !strcmp(s, "sw") ||
-		!strcmp(s, "hw") || !strcmp(s, "hw-romcode"))
+
+	if (!strcmp(s, "sw"))
+		gpmc_nand_data->ecc_opt = OMAP_ECC_HAM1_CODE_SW;
+	else if (!strcmp(s, "ham1") ||
+		 !strcmp(s, "hw") || !strcmp(s, "hw-romcode"))
 		gpmc_nand_data->ecc_opt =
 				OMAP_ECC_HAM1_CODE_HW;
 	else if (!strcmp(s, "bch4"))
-- 
1.8.3.2

[PATCH 3/3] ARM: dts: omap3430-sdp: Revert to using software ECC for NAND

[Roger Quadros]

For v3.14 and prior, 1-bit Hamming code ECC via software was used
for NAND on this board.
Commit c06c52701695 in v3.15 changed the behaviour
to use 1-bit Hamming code via Hardware using a different ECC layout
i.e. (ROM code layout) than what is used by software ECC.

This ECC layout change causes NAND filesystems created in v3.14
and prior to be unusable in v3.15 and later. So revert back to
using software ECC scheme.

Signed-off-by: Roger Quadros <rogerq@ti.com>
---
 arch/arm/boot/dts/omap3430-sdp.dts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/omap3430-sdp.dts b/arch/arm/boot/dts/omap3430-sdp.dts
index 02f69f4..9bad94e 100644
--- a/arch/arm/boot/dts/omap3430-sdp.dts
+++ b/arch/arm/boot/dts/omap3430-sdp.dts
@@ -107,7 +107,7 @@
 		#address-cells = <1>;
 		#size-cells = <1>;
 		reg = <1 0 0x08000000>;
-		ti,nand-ecc-opt = "ham1";
+		ti,nand-ecc-opt = "sw";
 		nand-bus-width = <8>;
 		gpmc,cs-on-ns = <0>;
 		gpmc,cs-rd-off-ns = <36>;
-- 
1.8.3.2