GPMI-NAND: Wrong ECC size in driver

GPMI-NAND: Wrong ECC size in driver

[Marek Vasut]

Hi,

the gpmi-nand.c driver apparently has misconfigured ecc.size field:

drivers/mtd/nand/gpmi-nand/gpmi-nand.c:
---------- >8 ----------
1493         chip->ecc.mode          = NAND_ECC_HW;
1494         chip->ecc.size          = 1;
1495         chip->ecc.layout        = &gpmi_hw_ecclayout;
---------- 8< ----------

This boils down to misconfigured mtd->subpage_sft in:

drivers/mtd/nand/nand_base.c:
---------- >8 ----------
3434         /* Allow subpage writes up to ecc.steps. Not possible for MLC flash 
*/
3435         if (!(chip->options & NAND_NO_SUBPAGE_WRITE) &&
3436             !(chip->cellinfo & NAND_CI_CELLTYPE_MSK)) {
3437                 switch (chip->ecc.steps) {
3438                 case 2:
3439                         mtd->subpage_sft = 1;
3440                         break;
3441                 case 4:
3442                 case 8:
3443                 case 16:
3444                         mtd->subpage_sft = 2;
3445                         break;
3446                 }
3447         }
3448         chip->subpagesize = mtd->writesize >> mtd->subpage_sft;
---------- 8< ----------

The mtd->subpage_sft is accidentally 0 by default. Therefore, the subpage size 
is mtd->writesize >> 0. Therefore the subpage size reported to UBI formating 
tools is the size of whole page, which works. Now, if I correct the problem by 
setting ecc.size properly to 512 bytes, I get into trouble with UBI:

1) UBI formating tools are reported the driver CAN DO subpage writes
2) UBI formating tools are reported the subpage size is 512 bytes

and this happens even though the NAND_NO_SUBPAGE_WRITE option is set by the 
driver. This is because:

drivers/mtd/nand/nand_base.c:
---------- >8 ----------
3072         /* Get chip options, preserve non chip based options */
3073         chip->options &= ~NAND_CHIPOPTIONS_MSK;
3074         chip->options |= type->options & NAND_CHIPOPTIONS_MSK;
---------- 8< ----------

which effectively masks that bit away. So, how are we going to fix it?

Cheers!

Marek

Re: GPMI-NAND: Wrong ECC size in driver

[Huang Shijie]

Hi Marek:
> Hi,
>
> the gpmi-nand.c driver apparently has misconfigured ecc.size field:
>
> drivers/mtd/nand/gpmi-nand/gpmi-nand.c:
> ---------->8 ----------
> 1493         chip->ecc.mode          = NAND_ECC_HW;
> 1494         chip->ecc.size          = 1;
> 1495         chip->ecc.layout        =&gpmi_hw_ecclayout;
> ---------- 8<  ----------
>
> This boils down to misconfigured mtd->subpage_sft in:
>
> drivers/mtd/nand/nand_base.c:
> ---------->8 ----------
> 3434         /* Allow subpage writes up to ecc.steps. Not possible for MLC flash
> */
> 3435         if (!(chip->options&  NAND_NO_SUBPAGE_WRITE)&&
> 3436             !(chip->cellinfo&  NAND_CI_CELLTYPE_MSK)) {
> 3437                 switch (chip->ecc.steps) {
> 3438                 case 2:
> 3439                         mtd->subpage_sft = 1;
> 3440                         break;
> 3441                 case 4:
> 3442                 case 8:
> 3443                 case 16:
> 3444                         mtd->subpage_sft = 2;
> 3445                         break;
> 3446                 }
> 3447         }
> 3448         chip->subpagesize = mtd->writesize>>  mtd->subpage_sft;
> ---------- 8<  ----------
>
> The mtd->subpage_sft is accidentally 0 by default. Therefore, the subpage size
> is mtd->writesize>>  0. Therefore the subpage size reported to UBI formating
> tools is the size of whole page, which works. Now, if I correct the problem by
> setting ecc.size properly to 512 bytes, I get into trouble with UBI:
>
> 1) UBI formating tools are reported the driver CAN DO subpage writes
> 2) UBI formating tools are reported the subpage size is 512 bytes
>
The gpmi driver does not support the subpage read/write.
I will be happy if the driver works only by setting the 
NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.

Best Regards
Huang Shijie
> and this happens even though the NAND_NO_SUBPAGE_WRITE option is set by the
> driver. This is because:
>
> drivers/mtd/nand/nand_base.c:
> ---------->8 ----------
> 3072         /* Get chip options, preserve non chip based options */
> 3073         chip->options&= ~NAND_CHIPOPTIONS_MSK;
> 3074         chip->options |= type->options&  NAND_CHIPOPTIONS_MSK;
> ---------- 8<  ----------
>
> which effectively masks that bit away. So, how are we going to fix it?
>
> Cheers!
>
> Marek
>

Re: GPMI-NAND: Wrong ECC size in driver

[Scott Wood]

On 01/03/2012 11:58 PM, Huang Shijie wrote:
> Hi Marek:
>> Hi,
>>
>> the gpmi-nand.c driver apparently has misconfigured ecc.size field:
>>
>> drivers/mtd/nand/gpmi-nand/gpmi-nand.c:
>> ---------->8 ----------
>> 1493         chip->ecc.mode          = NAND_ECC_HW;
>> 1494         chip->ecc.size          = 1;
>> 1495         chip->ecc.layout        =&gpmi_hw_ecclayout;
>> ---------- 8<  ----------
[snip]
> The gpmi driver does not support the subpage read/write.
> I will be happy if the driver works only by setting the
> NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.

Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers won't
set options that aren't appropriate?  Possibly replace it with
documentation about which options are for chips, which are for drivers,
and which (such as NAND_NO_SUBPAGE_WRITE) can be set by either.

-Scott

Re: GPMI-NAND: Wrong ECC size in driver

[Marek Vasut]

> On 01/03/2012 11:58 PM, Huang Shijie wrote:
> > Hi Marek:
> >> Hi,
> >> 
> >> the gpmi-nand.c driver apparently has misconfigured ecc.size field:
> >> 
> >> drivers/mtd/nand/gpmi-nand/gpmi-nand.c:
> >> ---------->8 ----------
> >> 1493         chip->ecc.mode          = NAND_ECC_HW;
> >> 1494         chip->ecc.size          = 1;
> >> 1495         chip->ecc.layout        =&gpmi_hw_ecclayout;
> >> ---------- 8<  ----------
> 
> [snip]
> 
> > The gpmi driver does not support the subpage read/write.
> > I will be happy if the driver works only by setting the
> > NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.
> 
> Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers won't
> set options that aren't appropriate?  Possibly replace it with
> documentation about which options are for chips, which are for drivers,
> and which (such as NAND_NO_SUBPAGE_WRITE) can be set by either.

Rather let's just adjust the mask?

M
> 
> -Scott

Re: GPMI-NAND: Wrong ECC size in driver

[Scott Wood]

On 01/04/2012 03:32 PM, Marek Vasut wrote:
>> On 01/03/2012 11:58 PM, Huang Shijie wrote:
>>> Hi Marek:
>>>> Hi,
>>>>
>>>> the gpmi-nand.c driver apparently has misconfigured ecc.size field:
>>>>
>>>> drivers/mtd/nand/gpmi-nand/gpmi-nand.c:
>>>> ---------->8 ----------
>>>> 1493         chip->ecc.mode          = NAND_ECC_HW;
>>>> 1494         chip->ecc.size          = 1;
>>>> 1495         chip->ecc.layout        =&gpmi_hw_ecclayout;
>>>> ---------- 8<  ----------
>>
>> [snip]
>>
>>> The gpmi driver does not support the subpage read/write.
>>> I will be happy if the driver works only by setting the
>>> NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.
>>
>> Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers won't
>> set options that aren't appropriate?  Possibly replace it with
>> documentation about which options are for chips, which are for drivers,
>> and which (such as NAND_NO_SUBPAGE_WRITE) can be set by either.
> 
> Rather let's just adjust the mask?

The way the mask is used means that any given option can only be chip or
driver, not both.  Though, I don't see anywhere this option is set by a
chip -- maybe we can just renumber it to be in the controller half.

I still don't see a whole lot of value in the mask, though -- seems to
be just causing problems, especially given that bits set by the "wrong"
component are silently discarded.

-Scott

Re: GPMI-NAND: Wrong ECC size in driver

[Marek Vasut]

> On 01/04/2012 03:32 PM, Marek Vasut wrote:
> >> On 01/03/2012 11:58 PM, Huang Shijie wrote:
> >>> Hi Marek:
> >>>> Hi,
> >>>> 
> >>>> the gpmi-nand.c driver apparently has misconfigured ecc.size field:
> >>>> 
> >>>> drivers/mtd/nand/gpmi-nand/gpmi-nand.c:
> >>>> ---------->8 ----------
> >>>> 1493         chip->ecc.mode          = NAND_ECC_HW;
> >>>> 1494         chip->ecc.size          = 1;
> >>>> 1495         chip->ecc.layout        =&gpmi_hw_ecclayout;
> >>>> ---------- 8<  ----------
> >> 
> >> [snip]
> >> 
> >>> The gpmi driver does not support the subpage read/write.
> >>> I will be happy if the driver works only by setting the
> >>> NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.
> >> 
> >> Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers won't
> >> set options that aren't appropriate?  Possibly replace it with
> >> documentation about which options are for chips, which are for drivers,
> >> and which (such as NAND_NO_SUBPAGE_WRITE) can be set by either.
> > 
> > Rather let's just adjust the mask?
> 
> The way the mask is used means that any given option can only be chip or
> driver, not both.  Though, I don't see anywhere this option is set by a
> chip -- maybe we can just renumber it to be in the controller half.

I suspect this was meant to allow controllers where one chip can do subpage-
write and the other can not.

> 
> I still don't see a whole lot of value in the mask, though -- seems to
> be just causing problems, especially given that bits set by the "wrong"
> component are silently discarded.

Yes. Patch is welcome to remove it and separate these two ;-)

M
> 
> -Scott

Re: GPMI-NAND: Wrong ECC size in driver

[Scott Wood]

On 01/04/2012 05:38 PM, Marek Vasut wrote:
> Scott Wood wrote:
>> On 01/04/2012 03:32 PM, Marek Vasut wrote:
>>> Scott Wood wrote:
>>>> Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers won't
>>>> set options that aren't appropriate?  Possibly replace it with
>>>> documentation about which options are for chips, which are for drivers,
>>>> and which (such as NAND_NO_SUBPAGE_WRITE) can be set by either.
>>>
>>> Rather let's just adjust the mask?
>>
>> The way the mask is used means that any given option can only be chip or
>> driver, not both.  Though, I don't see anywhere this option is set by a
>> chip -- maybe we can just renumber it to be in the controller half.
> 
> I suspect this was meant to allow controllers where one chip can do subpage-
> write and the other can not.

What I mean is I don't see any place where this is actually used --
gpmi-nand is the only place I see this flag being set (though it belongs
on at least elbc as well).

>> I still don't see a whole lot of value in the mask, though -- seems to
>> be just causing problems, especially given that bits set by the "wrong"
>> component are silently discarded.
> 
> Yes. Patch is welcome to remove it and separate these two ;-)

Do they need to be separated?  Just OR them with no mask.  If either the
controller or the chip set the flag, then it's set, and subpage writes
are disallowed.  Obviously you can only do this for certain types of
options -- for others, just don't set the flag in an inappropriate context.

-Scott

Re: GPMI-NAND: Wrong ECC size in driver

[Marek Vasut]

> On 01/04/2012 05:38 PM, Marek Vasut wrote:
> > Scott Wood wrote:
> >> On 01/04/2012 03:32 PM, Marek Vasut wrote:
> >>> Scott Wood wrote:
> >>>> Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers
> >>>> won't set options that aren't appropriate?  Possibly replace it with
> >>>> documentation about which options are for chips, which are for
> >>>> drivers, and which (such as NAND_NO_SUBPAGE_WRITE) can be set by
> >>>> either.
> >>> 
> >>> Rather let's just adjust the mask?
> >> 
> >> The way the mask is used means that any given option can only be chip or
> >> driver, not both.  Though, I don't see anywhere this option is set by a
> >> chip -- maybe we can just renumber it to be in the controller half.
> > 
> > I suspect this was meant to allow controllers where one chip can do
> > subpage- write and the other can not.
> 
> What I mean is I don't see any place where this is actually used --
> gpmi-nand is the only place I see this flag being set (though it belongs
> on at least elbc as well).
> 
> >> I still don't see a whole lot of value in the mask, though -- seems to
> >> be just causing problems, especially given that bits set by the "wrong"
> >> component are silently discarded.
> > 
> > Yes. Patch is welcome to remove it and separate these two ;-)
> 
> Do they need to be separated?  Just OR them with no mask.  If either the
> controller or the chip set the flag, then it's set, and subpage writes
> are disallowed.  Obviously you can only do this for certain types of
> options -- for others, just don't set the flag in an inappropriate context.
> 
> -Scott

BUMP?

Re: GPMI-NAND: Wrong ECC size in driver

[Brian Norris]

On 1/31/2012 3:33 AM, Marek Vasut wrote:
>> On 01/04/2012 05:38 PM, Marek Vasut wrote:
>>> Scott Wood wrote:
>>>> On 01/04/2012 03:32 PM, Marek Vasut wrote:
>>>>> Scott Wood wrote:
>>>>>> Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers
>>>>>> won't set options that aren't appropriate?  Possibly replace it with
>>>>>> documentation about which options are for chips, which are for
>>>>>> drivers, and which (such as NAND_NO_SUBPAGE_WRITE) can be set by
>>>>>> either.
>>>>>
>>>>> Rather let's just adjust the mask?
>>>>
>>>> The way the mask is used means that any given option can only be chip or
>>>> driver, not both.  Though, I don't see anywhere this option is set by a
>>>> chip -- maybe we can just renumber it to be in the controller half.
>>>
>>> I suspect this was meant to allow controllers where one chip can do
>>> subpage- write and the other can not.
>>
>> What I mean is I don't see any place where this is actually used --
>> gpmi-nand is the only place I see this flag being set (though it belongs
>> on at least elbc as well).

It is used out-of-tree as well (as mentioned below).

>>>> I still don't see a whole lot of value in the mask, though -- seems to
>>>> be just causing problems, especially given that bits set by the "wrong"
>>>> component are silently discarded.
>>>
>>> Yes. Patch is welcome to remove it and separate these two ;-)
>>
>> Do they need to be separated?  Just OR them with no mask.  If either the
>> controller or the chip set the flag, then it's set, and subpage writes
>> are disallowed.  Obviously you can only do this for certain types of
>> options -- for others, just don't set the flag in an inappropriate context.
>>
>> -Scott
>
> BUMP?

There's another distinct possibility (one that I use on an out-of-tree 
driver): instead of calling "nand_scan()", separate it into its two 
sub-functions "nand_scan_ident()" and "nand_scan_tail()" so you have 
something like this

     ret = nand_scan_ident(mtd, pdata->max_chip_count, NULL);
     chip->options |= NAND_NO_SUBPAGE_WRITE;
     if (!ret)
             ret = nand_scan_tail(mtd);

That way your option is set after we mask with NAND_CHIPOPTIONS_MSK. I'm 
not sure if this solution is better than really trying to tackle the 
issue of why we have that mask and whether it is still needed, but it 
solves the problem.

Brian

Re: GPMI-NAND: Wrong ECC size in driver

[Scott Wood]

On 01/31/2012 11:30 AM, Brian Norris wrote:
> There's another distinct possibility (one that I use on an out-of-tree
> driver): instead of calling "nand_scan()", separate it into its two
> sub-functions "nand_scan_ident()" and "nand_scan_tail()" so you have
> something like this
> 
>     ret = nand_scan_ident(mtd, pdata->max_chip_count, NULL);
>     chip->options |= NAND_NO_SUBPAGE_WRITE;
>     if (!ret)
>             ret = nand_scan_tail(mtd);
> 
> That way your option is set after we mask with NAND_CHIPOPTIONS_MSK. I'm
> not sure if this solution is better than really trying to tackle the
> issue of why we have that mask and whether it is still needed, but it
> solves the problem.


It's a bit hackish, but should work.  Why not get just rid of the mask,
though, if it's not actually doing anything constructive and is
requiring such workarounds?

-Scott

Re: GPMI-NAND: Wrong ECC size in driver

[Brian Norris]

On Tue, Jan 31, 2012 at 11:09 AM, Scott Wood <scottwood@freescale.com> wrote:
> On 01/31/2012 11:30 AM, Brian Norris wrote:
>> There's another distinct possibility (one that I use on an out-of-tree
>> driver): instead of calling "nand_scan()", separate it into its two
>> sub-functions "nand_scan_ident()" and "nand_scan_tail()" so you have
>> something like this
>>
>>     ret = nand_scan_ident(mtd, pdata->max_chip_count, NULL);
>>     chip->options |= NAND_NO_SUBPAGE_WRITE;
>>     if (!ret)
>>             ret = nand_scan_tail(mtd);
>>
>> That way your option is set after we mask with NAND_CHIPOPTIONS_MSK. I'm
>> not sure if this solution is better than really trying to tackle the
>> issue of why we have that mask and whether it is still needed, but it
>> solves the problem.
>
>
> It's a bit hackish, but should work.  Why not get just rid of the mask,
> though, if it's not actually doing anything constructive and is
> requiring such workarounds?

I'm not sure "why not." I hadn't looked at it in enough detail to tell
for sure. I was just providing my own solution, which doesn't require
any big system changes.

And actually, I think that my solution isn't really too "hackish." I
believe nand_scan_ident() and nand_scan_tail() are intentionally
exported separately to support some driver-level tweaking between the
initialization steps. For instance, my systems use the
nand_base-detected parameters (size, page size, etc.) to initialize
controller values before continuing to the tail, where we build our
BBT. I don't see why other options can't be tweaked here as well.

But I do see how, on a system that otherwise could use the default
nand_scan() interface, it seems counterintuitive that you cannot set
NAND_NO_SUBPAGE_WRITE before scanning.

Brian

Re: GPMI-NAND: Wrong ECC size in driver

[Brian Norris]

On Wed, Jan 4, 2012 at 3:48 PM, Scott Wood <scottwood@freescale.com> wrote:
> On 01/04/2012 05:38 PM, Marek Vasut wrote:
>> Scott Wood wrote:
>>> On 01/04/2012 03:32 PM, Marek Vasut wrote:
>>>> Scott Wood wrote:
>>>>> Can we just get rid of NAND_CHIPOPTIONS_MSK and trust that drivers won't
>>>>> set options that aren't appropriate?  Possibly replace it with
>>>>> documentation about which options are for chips, which are for drivers,
>>>>> and which (such as NAND_NO_SUBPAGE_WRITE) can be set by either.
>>>>
>>>> Rather let's just adjust the mask?
>>>
>>> The way the mask is used means that any given option can only be chip or
>>> driver, not both.  Though, I don't see anywhere this option is set by a
>>> chip -- maybe we can just renumber it to be in the controller half.
>>
>> I suspect this was meant to allow controllers where one chip can do subpage-
>> write and the other can not.
>
> What I mean is I don't see any place where this is actually used --
> gpmi-nand is the only place I see this flag being set (though it belongs
> on at least elbc as well).

It's never actually set per-chip (i.e., it's not in the nand_ids table
or similar), so I don't see a problem with Scott's suggestion: "maybe
we can just renumber it to be in the controller half." But that may
not be the best way (see below)

>>> I still don't see a whole lot of value in the mask, though -- seems to
>>> be just causing problems, especially given that bits set by the "wrong"
>>> component are silently discarded.
>>
>> Yes. Patch is welcome to remove it and separate these two ;-)
>
> Do they need to be separated?  Just OR them with no mask.  If either the
> controller or the chip set the flag, then it's set, and subpage writes
> are disallowed.  Obviously you can only do this for certain types of
> options -- for others, just don't set the flag in an inappropriate context.

It looks like this might work as well. Now that I look at the code a
bit, it seems that there's at least one other option
(NAND_NO_AUTOINCR) which is sometimes set by the controller *and*
per-chip (in nand_ids.c) but the per-chip option will always be
silently masked out in nand_base.c:

  chip->options |= type->options & NAND_CHIPOPTIONS_MSK;

But it also seems that NAND_NO_AUTOINCR has no effect in the kernel
anyway... (seems like we should just kill the option, then, right? But
I digress...)

So there seems to be more than one issue related to a mostly
unnecessary mask, and unless there's a strong reason against it, I
like Scott's last suggestions a little better ("Just OR them with no
mask" and "just don't set the flag in an inappropriate context").

Brian

Re: GPMI-NAND: Wrong ECC size in driver

[Marek Vasut]

> Hi Marek:
> > Hi,
> > 
> > the gpmi-nand.c driver apparently has misconfigured ecc.size field:
> > 
> > drivers/mtd/nand/gpmi-nand/gpmi-nand.c:
> > ---------->8 ----------
> > 1493         chip->ecc.mode          = NAND_ECC_HW;
> > 1494         chip->ecc.size          = 1;
> > 1495         chip->ecc.layout        =&gpmi_hw_ecclayout;
> > ---------- 8<  ----------
> > 
> > This boils down to misconfigured mtd->subpage_sft in:
> > 
> > drivers/mtd/nand/nand_base.c:
> > ---------->8 ----------
> > 3434         /* Allow subpage writes up to ecc.steps. Not possible for
> > MLC flash */
> > 3435         if (!(chip->options&  NAND_NO_SUBPAGE_WRITE)&&
> > 3436             !(chip->cellinfo&  NAND_CI_CELLTYPE_MSK)) {
> > 3437                 switch (chip->ecc.steps) {
> > 3438                 case 2:
> > 3439                         mtd->subpage_sft = 1;
> > 3440                         break;
> > 3441                 case 4:
> > 3442                 case 8:
> > 3443                 case 16:
> > 3444                         mtd->subpage_sft = 2;
> > 3445                         break;
> > 3446                 }
> > 3447         }
> > 3448         chip->subpagesize = mtd->writesize>>  mtd->subpage_sft;
> > ---------- 8<  ----------
> > 
> > The mtd->subpage_sft is accidentally 0 by default. Therefore, the subpage
> > size is mtd->writesize>>  0. Therefore the subpage size reported to UBI
> > formating tools is the size of whole page, which works. Now, if I
> > correct the problem by setting ecc.size properly to 512 bytes, I get
> > into trouble with UBI:
> > 
> > 1) UBI formating tools are reported the driver CAN DO subpage writes
> > 2) UBI formating tools are reported the subpage size is 512 bytes
> 
> The gpmi driver does not support the subpage read/write.

That's what I said above.

> I will be happy if the driver works only by setting the
> NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.

So you intentionally set the ecc.size to 1 to work around the issue?

> 
> Best Regards
> Huang Shijie
> 
> > and this happens even though the NAND_NO_SUBPAGE_WRITE option is set by
> > the driver. This is because:
> > 
> > drivers/mtd/nand/nand_base.c:
> > ---------->8 ----------
> > 3072         /* Get chip options, preserve non chip based options */
> > 3073         chip->options&= ~NAND_CHIPOPTIONS_MSK;
> > 3074         chip->options |= type->options&  NAND_CHIPOPTIONS_MSK;
> > ---------- 8<  ----------
> > 
> > which effectively masks that bit away. So, how are we going to fix it?
> > 
> > Cheers!
> > 
> > Marek

Re: GPMI-NAND: Wrong ECC size in driver

[Huang Shijie]

Hi,
>> I will be happy if the driver works only by setting the
>> >  NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.
> So you intentionally set the ecc.size to 1 to work around the issue?
>
yes.
I read the code, and it seemed setting the ecc.size to 1 is the right 
solution.

Best Regards
Huang Shijie

Re: GPMI-NAND: Wrong ECC size in driver

[Marek Vasut]

> Hi,
> 
> >> I will be happy if the driver works only by setting the
> >> 
> >> >  NAND_NO_SUBPAGE_WRITE, without setting the ecc.size.
> > 
> > So you intentionally set the ecc.size to 1 to work around the issue?
> 
> yes.
> I read the code, and it seemed setting the ecc.size to 1 is the right
> solution.
> 
> Best Regards
> Huang Shijie

It's definitelly wrong because it relies on undefined behaviour! The right 
solution here is to fix NAND_NO_SUBPAGE_WRITE pass-through as Scott and I 
proposed.

M