linux-kernel - Re: [PATCH v1] mtd: rawnand: micron: don't error out if internal ECC is set

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Date:   Fri, 17 Jan 2020 08:10:26 +0100
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     zdhays@...il.com, zhays@...mark.com,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Piotr Sroka <piotrs@...ence.com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mtd: rawnand: micron: don't error out if internal ECC
 is set

Hi Zak, Miquel,

On 20-01-16 19:22, Miquel Raynal wrote:
> Hi Zak,
> 
> zdhays@...il.com wrote on Fri, 10 Jan 2020 11:25:01 -0500:
> 
> > From: Zak Hays <zdhays@...il.com>
> > 
> > Recent changes to the driver require use of on-die correction if
> > the internal ECC enable bit is set. On some Micron parts, this bit
> > is enabled by default and there is no method for disabling it.

Which changes did you mean here?

> > This is a false assumption though as that bit being enabled does not
> > necessarily mean that the on-die ECC *has* to be used. It has been
> > verified with a Micron FAE that other methods of error correction are
> > still valid even if this bit is set.

It would be cool if a micron FAE can provide a document with all the
quirks and how those quirks can be handled.

> > HW ECC offers generally higher performance than on-die so it is
> > preferred in some situations. This also allows multiple NAND parts to
> > be supported on the same PCB as some parts may not support on-die
> > error correction.

By HW ECC you mean the host ecc controller?

> > With that in mind, only throw a warning that the on-die bit is set
> > and allow the init to continue.
> 
> I don't think I can take this patch as-is. We must find a reliable way
> to discriminate Micron parts features. If we cannot (I think we can't
> before of the endless list of bugs they have introduced without
> documenting them), the best way is to build a static table.

+1 for 'find a reliable way to discriminate Micron parts features'

Regards,
  Marco

> > 
> > Signed-off-by: Zak Hays <zdhays@...il.com>
> > ---
> >  drivers/mtd/nand/raw/nand_micron.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
> > index 56654030ec7f..ec40c76443be 100644
> > --- a/drivers/mtd/nand/raw/nand_micron.c
> > +++ b/drivers/mtd/nand/raw/nand_micron.c
> > @@ -455,9 +455,7 @@ static int micron_nand_init(struct nand_chip *chip)
> >  
> >  	if (ondie == MICRON_ON_DIE_MANDATORY &&
> >  	    chip->ecc.mode != NAND_ECC_ON_DIE) {
> > -		pr_err("On-die ECC forcefully enabled, not supported\n");
> > -		ret = -EINVAL;
> > -		goto err_free_manuf_data;
> > +		pr_warn("WARNING: On-die ECC forcefully enabled, use caution with other methods\n");
> >  	}
> >  
> >  	if (chip->ecc.mode == NAND_ECC_ON_DIE) {
> 
> Thanks,
> Miquèl
> 

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