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

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Message-ID: <CANZat+g=emsHmx7i4mEzTXh1s2=t8Bw7cmXYd0YUXKt_oNh-rA@mail.gmail.com>
Date:   Fri, 17 Jan 2020 14:32:54 -0500
From:   Zak Hays <zdhays@...il.com>
To:     Marco Felsch <m.felsch@...gutronix.de>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Zak Hays <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 Marco & Miquel,

On Fri, Jan 17, 2020 at 2:10 AM Marco Felsch <m.felsch@...gutronix.de> wrote:
>
> 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?

I was referring to the combination of these two patches:

9748e1d87573  Thomas Petazzoni  mtd: nand: add support for Micron on-die ECC
cb2bf403a462  Chris Packham  mtd: rawnand: micron: allow forced on-die ECC

>
> > > 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.
>

Agreed. I'll ask my contact at Micron if such a document exists and
if they would be willing to share it.

> > > 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?
>

Yes. I used the term HW ECC as that is how it is referenced in the
device tree (nand-ecc-mode = "hw") and the driver (NAND_ECC_HW).

> > > 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.
>

That's understandable. I'll look into this a little more and see if it's
feasible to implement a static table to handle this.

Thanks,
Zak


On Fri, Jan 17, 2020 at 2:28 PM Zak Hays <zdhays@...il.com> wrote:
>
> Hi Marco & Miquel,
>
> On Fri, Jan 17, 2020 at 2:10 AM Marco Felsch <m.felsch@...gutronix.de> wrote:
> >
> > 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?
>
> I was referring to the combination of these two patches:
>
> 9748e1d87573  Thomas Petazzoni  mtd: nand: add support for Micron on-die ECC
> cb2bf403a462  Chris Packham  mtd: rawnand: micron: allow forced on-die ECC
>
> >
> > > > 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.
> >
>
> Agreed. I'll ask my contact at Micron if such a document exists and
> if they would be willing to share it.
>
> > > > 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?
> >
>
> Yes. I used the term HW ECC as that is how it is referenced in the
> device tree (nand-ecc-mode = "hw") and the driver (NAND_ECC_HW).
>
> > > > 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.
> >
>
> That's understandable. I'll look into this a little more and see if it's
> feasible to implement a static table to handle this.
>
> Thanks,
> Zak