Re: [PATCH] mtd: rawnand: micron: handle "ecc off" devices correctly

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 26 Jul 2019 10:34:41 +0200
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> + Actual address for Boris
> 
> Miquel Raynal <miquel.raynal@bootlin.com> wrote on Fri, 26 Jul 2019
> 10:28:58 +0200:
> 
> > Hi Marco,
> > 
> > + Richard
> > + Working e-mail address for Boris
> > 
> > Marco Felsch <m.felsch@pengutronix.de> wrote on Fri, 26 Jul 2019
> > 09:44:34 +0200:
> >   
> > > Some devices don't support ecc "official". By "official" I mean that the
> > > feature can be set trough the "SET FEATURE (EFh)" command but isn't
> > > reported to the "READ ID Parameter Tables". Because the "ECC Field"
> > > still says that it is disabled. This is applicable at least
> > > for the MT29F2G08ABAGA and MT29F2G08ABBGA devices. Even worse the
> > > datasheet describes the ECC feature in chapter "ECC Protection".
> > > 
> > > Currently the driver checks the "READ ID Parameter" field directly after
> > > we enabled the feature. If the check fails we return immediately but
> > > leave the ECC on. Now all future read/program cycles goes trough the ecc
> > > and the host nfc gets confused and reports ECC errors.
> > > 
> > > To address this in a common way we need to turn off the ECC directly
> > > after reading the "READ ID Parameter" and before checking the
> > > "ECC status".
> > > 
> > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>  

Duh! Yet another bug on those Micron chips. I can't say I'm
surprised :-).

Anyway, the change looks good:

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> > 
> > Good catch! However you report that on-die ECC correction is working
> > but you still disable it; any reason to do so ? Would it be better to
> > actually enable on-die ECC and explicitly mark these two chips as
> > buggy (see [1] for checking the chip IDs)?

That's a solution, but are we even sure ECC works correctly on those
NANDs? Given all the problem we have with on-die ECC on Micron chips I
think it might be a good thing to base the "on-die ECC support"
detection on the full ID (or even better, the part name provided by the
ONFi param page) instead of trying to be smart. This way we can
whitelist the NANDs that are known to work correctly and stop adding
more quirks every time we find a new bug...

> > 
> > [1] https://elixir.bootlin.com/linux/v5.3-rc1/source/drivers/mtd/nand/raw/nand_macronix.c#L83
> >   
> > > ---
> > >  drivers/mtd/nand/raw/nand_micron.c | 14 +++++++++++---
> > >  1 file changed, 11 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
> > > index 1622d3145587..fb199ad2f1a6 100644
> > > --- a/drivers/mtd/nand/raw/nand_micron.c
> > > +++ b/drivers/mtd/nand/raw/nand_micron.c
> > > @@ -390,6 +390,14 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
> > >  	    (chip->id.data[4] & MICRON_ID_INTERNAL_ECC_MASK) != 0x2)
> > >  		return MICRON_ON_DIE_UNSUPPORTED;
> > >  
> > > +	/*
> > > +	 * It seems that there are devices which do not support ECC official.
> > > +	 * At least the MT29F2G08ABAGA / MT29F2G08ABBGA devices supports
> > > +	 * enabling the ECC feature but don't reflect that to the READ_ID table.
> > > +	 * So we have to guarantee that we disable the ECC feature directly
> > > +	 * after we did the READ_ID table command. Later we can evaluate the
> > > +	 * ECC_ENABLE support.
> > > +	 */
> > >  	ret = micron_nand_on_die_ecc_setup(chip, true);
> > >  	if (ret)
> > >  		return MICRON_ON_DIE_UNSUPPORTED;
> > > @@ -398,13 +406,13 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
> > >  	if (ret)
> > >  		return MICRON_ON_DIE_UNSUPPORTED;
> > >  
> > > -	if (!(id[4] & MICRON_ID_ECC_ENABLED))
> > > -		return MICRON_ON_DIE_UNSUPPORTED;
> > > -
> > >  	ret = micron_nand_on_die_ecc_setup(chip, false);
> > >  	if (ret)
> > >  		return MICRON_ON_DIE_UNSUPPORTED;
> > >  
> > > +	if (!(id[4] & MICRON_ID_ECC_ENABLED))
> > > +		return MICRON_ON_DIE_UNSUPPORTED;
> > > +
> > >  	ret = nand_readid_op(chip, 0, id, sizeof(id));
> > >  	if (ret)
> > >  		return MICRON_ON_DIE_UNSUPPORTED;  
> > 
> > Thanks,
> > Miquèl  


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