[2/3] mtd: rawnand: micron: Disable ECC earlier in the read path

[Chris.Packham@xxxxxxxxxxxxxxxxxxx (Chris Packham)]

On 17/07/18 08:55, Boris Brezillon wrote:
> On Mon, 16 Jul 2018 18:10:57 +0200
> Boris Brezillon <boris.brezillon at bootlin.com> wrote:
> 
>> On Mon, 16 Jul 2018 09:00:59 +0000
>> Chris Packham <Chris.Packham at alliedtelesis.co.nz> wrote:
>>
>>> Hi Boris,
>>>
>>> On 04/07/18 00:20, Boris Brezillon wrote:
>>>> We are about to support extracting the real number of bitflips for
>>>> 4-bits ECC when WRITE_RECOMMEND is returned. This requires re-reading
>>>> the page in raw mode to compare it to the corrected version, and this
>>>> logic will be placed in micron_nand_on_die_ecc_status_4().
>>>>
>>>> Moving the micron_nand_on_die_ecc_setup() will allow us to disable
>>>> ECC only once.
>>>>
>>>> As a result, we have to rework the exit path and add an error path
>>>> where the ECC is disabled.
>>>>
>>>> Signed-off-by: Boris Brezillon <boris.brezillon at bootlin.com>
>>>
>>> As I said on the other thread this appears to cause a problem for me on
>>> the MT29F1G08ABAFAWP-ITE setup I have. I notice we're not able to find
>>> the BBT, not sure if that is symptom or cause.
> 
> It's most likely the symptom, not the cause.
> 
>>>>
>>>> diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
>>>> index 63ac98a36ed7..b9cbaf125a98 100644
>>>> --- a/drivers/mtd/nand/raw/nand_micron.c
>>>> +++ b/drivers/mtd/nand/raw/nand_micron.c
>>>> @@ -197,30 +197,37 @@ micron_nand_read_page_on_die_ecc(struct mtd_info *mtd, struct nand_chip *chip,
>>>>    
>>>>    	ret = nand_read_page_op(chip, page, 0, NULL, 0);
>>>>    	if (ret)
>>>> -		goto out;
>>>> +		goto err_disable_ecc;
>>>>    
>>>>    	ret = nand_status_op(chip, &status);
>>>>    	if (ret)
>>>> -		goto out;
>>>> +		goto err_disable_ecc;
>>>>    
>>>>    	ret = nand_exit_status_op(chip);
>>>>    	if (ret)
>>>> -		goto out;
>>>> +		goto err_disable_ecc;
>>>>    
>>>> -	if (chip->ecc.strength == 4)
>>>> -		max_bitflips = micron_nand_on_die_ecc_status_4(chip, status);
>>>> -	else
>>>> -		max_bitflips = micron_nand_on_die_ecc_status_8(chip, status);
>>>> +	micron_nand_on_die_ecc_setup(chip, false);
>>
>> Hm, can you try to move the micron_nand_on_die_ecc_setup(chip, false)
>> call just before nand_exit_status_op()?
>>
> 
> Just pushed a branch fixing that [1]. Can you test it? If it works,
> I'll ask Miquel to drop the initial set of patches and instead pick the
> fixed ones so that we don't break bisectibility.
> 
> [1]https://github.com/bbrezillon/linux-0day/commits/nand/next
> 

Still appears to have the same problem.

I'm guessing that since you can't actually disable ecc on this chip 
calling micron_nand_on_die_ecc_setup(chip, false); before reading the 
oob data interferes with it somehow (if I call it after there is no 
problem).

We could add code to qualify the attempt to disable ecc early based on 
it being optional/mandatory or just stick with it being disabled late.