Re: [PATCH v1 4/5] mtd: rawnand: meson: clear OOB buffer before read

[Arseniy Krasnov <avkrasnov@sberdevices.ru>]

On 02.05.2023 15:17, Miquel Raynal wrote:
> Hi Arseniy,
> 
> Richard, your input is welcome below :-)
> 
>>>>>>>>> I just checked JFFS2 mount/umount again, here is what i see:
>>>>>>>>> 0) First attempt to mount JFFS2.
>>>>>>>>> 1) It writes OOB to page N (i'm using raw write). It is cleanmarker value 0x85 0x19 0x03 0x20. Mount is done.
>>>>>>>>> 2) Umount JFFS2. Done.
>>>>>>>>> 3) Second attempt to mount JFFS2.
>>>>>>>>> 4) It reads OOB from page N (i'm using raw read). Value is 0x85 0x19 0x03 0x20. Done.
>>>>>>>>> 5) It reads page N in ECC mode, and i get:
>>>>>>>>>      jffs2: mtd->read(0x100 bytes from N) returned ECC error
>>>>>>>>> 6) Mount failed.
>>>>>>>>>
>>>>>>>>> We already had problem which looks like this on another device. Solution was to use OOB area which is
>>>>>>>>> not covered by ECC for JFFS2 cleanmarkers.      
>>>>>>>
>>>>>>> ok, so there is not ECC parity bytes and mtd->read() returns ECC error.
>>>>>>> does it have to use raw write/read on step 1) and 4)?
>>>>>>>       
>>>>>>
>>>>>> If i'm using non raw access to OOB, for example write OOB (user bytes) in ECC mode, then
>>>>>> steps 1) and 4) and 5) passes ok, but write to this page will be impossible (for example JFFS2
>>>>>> writes to such pages later) - we can't update ECC codes properly without erasing whole page.
>>>>>> Write operation will be done without problem, but read will trigger ECC errors due to broken
>>>>>> ECC codes.
>>>>>>
>>>>>> In general problem that we discuss is that in current implementation data and OOB conflicts
>>>>>> with each other by sharing same ECC codes, these ECC codes could be written only once (without
>>>>>> erasing), while data and OOB has different callbacks to access and thus supposed to work
>>>>>> separately.    
>>>>>
>>>>> The fact that there might be helpers just for writing OOB areas or just
>>>>> in-band areas are optimizations. NAND pages are meant to be written a
>>>>> single time, no matter what portion you write. In some cases, it is
>>>>> possible to perform subpage writes if the chip supports it. Pages may
>>>>> be split into several areas which cover a partial in-band area *and* a
>>>>> partial OOB area. If you write into the in-band *or* out-of-band areas
>>>>> of a given subpage, you *cannot* write the other part later without    
>>>>
>>>> Thanks for details! So in case of JFFS2 it looks like strange, that it tries
>>>> to write page after writing clean markers to it before? In the old vendor's
>>>> driver OOB write callback is suppressed by return 0 always and JFFS2 works
>>>> correctly.  
>>>
>>> Can you point the code you're mentioning? (both what JFFS2 which looks
>>> strange to you and the old vendor hack)  
>>
>> Here is version of the old vendor's driver:
>>
>> https://github.com/kszaq/linux-amlogic/blob/master_new_amports/drivers/amlogic/nand/nand/aml_nand.c#L3260
>>
>> In my version there is no BUG() there, but it is same driver for the same chip.
>>
>> About JFFS2 - i didn't check its source code, but what I can see using printk(), is that it first
>> tries to write cleanmarker using OOB write callback. Then later it tries to write to this page, so
>> may be it is unexpected behaviour of JFFS2?
> 
> TBH I am not knowledgeable about JFFS2, maybe Richard can help here.
> 
> Are you sure you flash is recognized by JFFS2 as being a NAND device?
> Did you enable CONFIG_JFFS2_FS_WRITEBUFFER correctly? Because
> cleanmarker seem to be discarded when using a NAND device, and
> recognizing the device as a NAND device requires the above option to be
> set apparently.

Yes, I have

CONFIG_JFFS2_FS_WRITEBUFFER=y

And i see, that jffs2_mark_erased_block() calls jffs2_cleanmarker_oob() which checks that we have MTD_NANDFLASH. This
check is true, so then jffs2_write_nand_cleanmarker() is called and there is OOB write in it. So I see opposite thing:
cleanmarkers are not discarded with NAND device. 

Thanks, Arseniy

> 
> Thanks,
> Miquèl

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