[U-Boot] [PATCH v2] pcm058: fix NAND flash not using badblock table

[Stefano Babic]

Hi Harald,

On 07/12/18 22:18, Harald Seiler wrote:
> Hello Stefano,
> 
> On Fri, 2018-12-07 at 19:55 +0100, Stefano Babic wrote:
>> Hi Harald,
>>
>> On 07/12/18 13:18, Marek Vasut wrote:
>>> On 12/07/2018 01:15 PM, Harald Seiler wrote:
>>>> Hello Marek,
>>>
>>> Hi,
>>>
>>>> On Fri, 2018-12-07 at 12:48 +0100, Marek Vasut wrote:
>>>>> On 12/07/2018 10:19 AM, Harald Seiler wrote:
>>>>>> Currently, U-Boot ignores the BBT stored in the last 4 blocks of NAND
>>>>>> flash because the NAND_BBT_USE_FLASH flag is not set.  This leads to
>>>>>> two issues:
>>>>>>
>>>>>> * U-Boot silently uses a memory-only BBT which is initialized with all
>>>>>>   blocks marked as good.  This means, actual bad blocks are marked good
>>>>>>   and U-Boot might try writing to or reading from them.
>>>>>> * The BBT in flash, which will be created once Linux boots up, is not
>>>>>>   off limits for a driver ontop, like UBI.  While it does not seem to
>>>>>>   consistently produce an error, sometimes UBI will fail to attach
>>>>>>   because the BBT blocks obviously don't contain valid UBI data.
>>>>>>
>>>>>> To fix this, this patch sets the CONFIG_SYS_NAND_USE_FLASH_BBT option,
>>>>>> which is used in ./drivers/mtd/nand/raw/mxs_nand.c to decide whether
>>>>>> a BBT in flash is used.
>>>>>>
>>>>>> Signed-off-by: Harald Seiler <hws at denx.de>
>>>>>
>>>>> V2 Changelog is missing.
>>>>>
>>>>>> ---
>>>>>>  include/configs/pcm058.h | 1 +
>>>>>>  1 file changed, 1 insertion(+)
>>>>>>
>>>>>> diff --git a/include/configs/pcm058.h b/include/configs/pcm058.h
>>>>>> index 49048c163f..b9bc08b388 100644
>>>>>> --- a/include/configs/pcm058.h
>>>>>> +++ b/include/configs/pcm058.h
>>>>>> @@ -55,6 +55,7 @@
>>>>>>  #define CONFIG_SYS_NAND_BASE		0x40000000
>>>>>>  #define CONFIG_SYS_NAND_5_ADDR_CYCLE
>>>>>>  #define CONFIG_SYS_NAND_ONFI_DETECTION
>>>>>> +#define CONFIG_SYS_NAND_USE_FLASH_BBT
>>>>>
>>>>> Shouldn't this be enabled on all boards with GPMI NAND ?
>>>>>
>>>>
>>>> I looked at other boards and they all defined this config, so I
>>>> assumed this was the way to go ...
>>
>> Let me understand. If Isearch for CONFIG_NAND_MXS, I get 27 boards using
>> this drivers, with different SOC (mx28, mx6[Dual|Quad|Solo], mx6sx,
>> mx6ull). But none of them is setting  CONFIG_SYS_NAND_USE_FLASH_BBT.
>>
>> When does it happen the issue ? It should happen if we create a UBI
>> container and its volumes in U-Boot. If UBI is generated in linux, this
>> should not happen. Is it the case or does it happen in any condition ?
> 
> Linux will write the badblock table to the last 4 blocks by default which
> U-Boot ignores at the moment.  So the issue happens if you use the default
> kernel config (which you pointed out below).

Right, or in any case where there is a mismatch in the configuration
between U-Boot and Linux.

> 
>> I think the issue happens because there is a disalignment between kernel
>> and u-boot. Kernel mainline for this board (file
>> imx6qdl-phytec-phycore-som.dtsi) sets "nand-on-flash-bbt", while U-Boot
>> not. That mean that this can always happen if kernel and U-Boot does not
>> use the same setup for the driver.
>>
>> Maybe with previous kernel versions there was no problem because Linux
>> used the same setup as U-Boot.
> 
> This is exactly what I think is going on ...

Right.

> 
>> Anyway, this discourage setting CONFIG_SYS_NAND_USE_FLASH_BBT
>> unconditionally for all boards with GPMI driver.
>>
> 
> I agree, it only makes sense in cases where Linux also does it this way.
> Although, not doing it this way means not having any persistent badblock
> table at all, which I feel is never a good idea ...
> 
>>> But yes, as far as I understand,
>>>> it would make sense to have it enabled most of the time.  Although
>>>> there is some code which makes this configuration from the
>>>> devicetree, which might be an even better solution.
>>
>> Device tree has already this option as I see in
>> drivers/mtd/nand/raw/nand_base.c. The driver enforces this if no DT (as
>> in this case) is used.
> 
> What do you mean by enforce? 

Without DT, behavior is decided at compile time.

> If no devicetree is used, the code does not
> set any flags as far as I understand it, which also aligns with the results
> of my experimentation ... (Currently bbt_options is 0)

Ok - we agree that this change cannot be done for all boards because it
depends if Linux is using or not, and we do not know the common use
cases for thoese boards. It must be decided any time by the board
maintainer (well, in this case me..). Use case for this board is running
kernel mainline, so it makes sense to apply this patch.

Regards,
Stefano

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