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Date: Tue, 31 Jul 2012 16:09:59 +0200
From: Matthieu CASTET <matthieu.castet@parrot.com>
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To: Marek Vasut <marex@denx.de>
Subject: Re: [PATCH RESEND] mtd: nand: allow NAND_NO_SUBPAGE_WRITE to be set
 from driver
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Marek Vasut a écrit :
> Dear Matthieu CASTET,
> 
>> Hi Marek,
>>
>> Marek Vasut a écrit :
>>> Dear Matthieu CASTET,
>>>
>>>> Hi,
>>>>
>>>> for ONFI flash (like this micron one) the information should be
>>>> extracted form the ONFI table (programs_per_page IIRC)
>>>>
>>>> This should be better than relying on the SOC driver for setting this
>>>> flags.
>>>>
>>>> Does the gpmi driver set this flag because it do not support partial
>>>> write ?
>>> Yes
>>>
>>>> In this case why it doesn't set  chip->ecc.steps to 1 ?
>>> Can you elabore how exactly will that help please?
>> If you look at the nand_base.c, you will see that mtd->subpage_sft = 0 if
>> NAND_NO_SUBPAGE_WRITE flags is set or chip->ecc.steps == 1 [1].
> 
> Ok, this is what I saw coming ... this is yet another hole in the design and I 
> see only undefined behavior. So if default: branch started returning an error, 
> this whole code will break again.
Do you see any reason why chip->ecc.steps == 1 will return an error ?
This will break drivers.

The behavior match the comment : "Allow subpage writes up to ecc.steps"

Matthieu
> 
> 
>> [1]
>>     /* Allow subpage writes up to ecc.steps. Not possible for MLC flash */
>>     if (!(chip->options & NAND_NO_SUBPAGE_WRITE) &&
>>         !(chip->cellinfo & NAND_CI_CELLTYPE_MSK)) {
>>         switch (chip->ecc.steps) {
>>         case 2:
>>             mtd->subpage_sft = 1;
>>             break;
>>         case 4:
>>         case 8:
>>         case 16:
>>             mtd->subpage_sft = 2;
>>             break;
>>         }
>>     }
>>     chip->subpagesize = mtd->writesize >> mtd->subpage_sft;