[U-Boot] NAND flash question

[U-Boot] NAND flash question

[ANDY KENNEDY]

All,

We have a design that has NAND as a secondary device (not the boot
device).  The last four pages of the NAND flash are reported as bad.
Should this be true for all NAND flash devices we have?

Thanks,
Andy

[U-Boot] NAND flash question

[Peter Barada]

On 09/19/2013 04:04 PM, ANDY KENNEDY wrote:
> All,
>
> We have a design that has NAND as a secondary device (not the boot
> device).  The last four pages of the NAND flash are reported as bad.
> Should this be true for all NAND flash devices we have?
>
>
No, I wouldn't think so.  Manufacturers qualify their parts and mark bad
blocks found during qualification testing.  Most data sheets indicate
that the number of bad blocks marked bad during manufacturer is below a
set percentage(if above thent he part is rejected).  Some parts that are
meant to be used during boot (such as NAND meant for OMAP parts) will
have certain blocks that are guaranteed good (i.e. the boot blocks). 
Past that bad blocks could be anywhere in a particular device.

-- 
Peter Barada
peter.barada at logicpd.com

[U-Boot] NAND flash question

[ANDY KENNEDY]

> -----Original Message-----
> From: u-boot-bounces at lists.denx.de [mailto:u-boot-bounces at lists.denx.de] On Behalf Of Peter Barada
> Sent: Thursday, September 19, 2013 3:26 PM
> To: u-boot at lists.denx.de; Peter Barada
> Subject: Re: [U-Boot] NAND flash question
> 
> On 09/19/2013 04:04 PM, ANDY KENNEDY wrote:
> > All,
> >
> > We have a design that has NAND as a secondary device (not the boot
> > device).  The last four pages of the NAND flash are reported as bad.
> > Should this be true for all NAND flash devices we have?
> >
> >
> No, I wouldn't think so.  Manufacturers qualify their parts and mark bad
> blocks found during qualification testing.  Most data sheets indicate
> that the number of bad blocks marked bad during manufacturer is below a
> set percentage(if above thent he part is rejected).  Some parts that are
> meant to be used during boot (such as NAND meant for OMAP parts) will
> have certain blocks that are guaranteed good (i.e. the boot blocks).
> Past that bad blocks could be anywhere in a particular device.
> 

Okay, well, next question:  So on EVERY unit we have designed with a
NAND flash, when u-Boot reads the NAND flash it reports that it couldn't
locate a bad block table and states that it cannot read the last four
pages of the flash.  Next, when one does a 'nand bad' on these boards,
these last four pages are reported by u-Boot as bad.  Looking at the
code, we believe that this is by design.  Is that correct?  Has anyone
else done a 'nand bad' on a board and seen the same information?

Thanks again for any information you can provide,

Andy

[U-Boot] NAND flash question

[Peter Barada]

On 09/20/2013 11:27 AM, ANDY KENNEDY wrote:
>> -----Original Message-----
>> From: u-boot-bounces at lists.denx.de [mailto:u-boot-bounces at lists.denx.de] On Behalf Of Peter Barada
>> Sent: Thursday, September 19, 2013 3:26 PM
>> To: u-boot at lists.denx.de; Peter Barada
>> Subject: Re: [U-Boot] NAND flash question
>>
>> On 09/19/2013 04:04 PM, ANDY KENNEDY wrote:
>>> All,
>>>
>>> We have a design that has NAND as a secondary device (not the boot
>>> device).  The last four pages of the NAND flash are reported as bad.
>>> Should this be true for all NAND flash devices we have?
>>>
>>>
>> No, I wouldn't think so.  Manufacturers qualify their parts and mark bad
>> blocks found during qualification testing.  Most data sheets indicate
>> that the number of bad blocks marked bad during manufacturer is below a
>> set percentage(if above thent he part is rejected).  Some parts that are
>> meant to be used during boot (such as NAND meant for OMAP parts) will
>> have certain blocks that are guaranteed good (i.e. the boot blocks).
>> Past that bad blocks could be anywhere in a particular device.
>>
> Okay, well, next question:  So on EVERY unit we have designed with a
> NAND flash, when u-Boot reads the NAND flash it reports that it couldn't
> locate a bad block table and states that it cannot read the last four
> pages of the flash.  Next, when one does a 'nand bad' on these boards,
> these last four pages are reported by u-Boot as bad.  Looking at the
> code, we believe that this is by design.  Is that correct?  Has anyone
> else done a 'nand bad' on a board and seen the same information?
>
> Thanks again for any information you can provide,
>
> Andy
If you are using a NAND-based bad block table (i.e. set the
NAND_USE_FLASH_BBT bit in nand->options), then the MTD layer will
internally use the last four blocks to hold the bad block table _and_
report those blocks as bad to prevent the user from accidentally
modifying them...



-- 
Peter Barada
peter.barada at logicpd.com