Re: [PATCH 1/9] mtd: nand: qcom: use the ecc strength from device parameter
From: Miquel Raynal
Date: Tue Apr 10 2018 - 03:56:19 EST
> Hi Abhishek,
>
> On Tue, 10 Apr 2018 11:39:35 +0530, Abhishek Sahu
> <absahu@xxxxxxxxxxxxxx> wrote:
>
> > On 2018-04-06 18:01, Miquel Raynal wrote:
> > > Hi Abhishek,
> > >
> > > On Wed, 4 Apr 2018 18:12:17 +0530, Abhishek Sahu
> > > <absahu@xxxxxxxxxxxxxx> wrote:
> > >
> > >> Currently the driver uses the ECC strength specified in
> > >> device tree. The ONFI or JEDEC device parameter page
> > >> contains the âECC correctabilityâ field which indicates the
> > >> number of bits that the host should be able to correct per
> > >> 512 bytes of data.
> > >
> > > This is misleading. This field is not about the controller but rather
> > > the chip requirements in terms of minimal strength for nominal use.
> > >
> >
> > Thanks Miquel.
> >
> > Yes. Its NAND chip requirement. I have used the description for
> > NAND ONFI param page
> >
> > 5.6.1.24. Byte 112: Number of bits ECC correctability
> > This field indicates the number of bits that the host should be
> > able to correct per 512 bytes of data.
> >
> > >> The ecc correctability is assigned in
> > >> chip parameter during device probe time. QPIC/EBI2 NAND
> > >> supports 4/8-bit ecc correction. The Same kind of board
> > >> can have different NAND parts so use the ecc strength
> > >> from device parameter (if its non zero) instead of
> > >> device tree.
> > >
> > > That is not what you do.
> > >
> > > What you do is forcing the strength to be 8-bit per ECC chunk if the
> > > NAND chip requires at least 8-bit/chunk strength.
> > >
> > > The DT property is here to force a strength. Otherwise, Linux will
> > > propose to the NAND controller to use the minimum strength required by
> > > the chip (from either the ONFI/JEDEC parameter page or from a static
> > > table).
> > >
> >
> > The main problem is that the same kind of boards can have different
> > NAND parts.
> >
> > Lets assume, we have following 2 cases.
> >
> > 1. Non ONFI/JEDEC device for which chip->ecc_strength_ds
> > will be zero. In this case, the ecc->strength from DT
> > will be used
>
> No, the strength from DT will always be used if the property is
> present, no matter the type of chip.
>
> > 2. ONFI/JEDEC device for which chip->ecc_strength_ds > 8.
> > Since QCOM nand controller can not support
> > ECC correction greater than 8 bits so we can use 8 bit ECC
> > itself instead of failing NAND boot completely.
>
> I understand that. But this is still not what you do.
>
> >
> > > IMHO, you have two solutions:
> > > 1/ Remove these properties from the board DT (breaks DT backward
> > > compatibility though);
> >
> > - nand-ecc-strength: This is optional property in nand.txt and
> > Required property in qcom_nandc.txt.
>
> Well, this property is not controller specific but chip specific. The
> controller driver does not rely on it, so this property should not be
> required.
>
> > We can't remove since
> > if the device is Non ONFI/JEDEC, then ecc strength will come
> > from DT only.
>
> We can remove it and let the core handle this (as this is generic to
> all raw NANDs and not specific to this controller driver). Try it out!
>
> However if the defaults value do not match your expectations, I think
> you can add your non-ONFI/JEDEC chip in 'nand_ids.c', this should fill
> your strength_ds field and let you avoid using these properties.
Actually nand_ids.c should not be filled anymore, instead you can
implement this detection thanks to the part full name in the vendor
code nand_samsung.c, nand_micron.c, nand_macronix.c, nand_hynix.c, etc.
Depending on what part you are using, it might already work.
>
> >
> > > 2/ Create another DT for the board.
> > >
> >
> > Its not about board but about part. We have IPQ8074 HK01 board
> > with 4 bit ECC chip/8 bit ECC chip/non ONFI/JEDEC chip.
> >
> > > However, there is something to do in this driver: the strength chosen
> > > should be limited to the controller capabilities (8-bit/512B if I
> > > understand correctly). In this case you have two options: either you
> > > limit the strength like the size [1] if (ecc->strength > 8);
> >
> > Limiting the strength will make all the boards with ecc strength > 8
> > to fail completely
> >
> > > just limit the maximum strength to 8 like this [2] and the core will
> > > spawn a warning in the dmesg telling that the ECC strength used is
> > > below the NAND chip requirements.
> >
> > Yes its good idea. I can update the patch with dmesg warning.
> >
> > Thanks,
> > Abhishek
> >
> > >
> > > Thanks,
> > > MiquÃl
> > >
> > > [1]
> > > https://elixir.bootlin.com/linux/latest/source/drivers/mtd/nand/qcom_nandc.c#L2332
> > > [2] http://code.bulix.org/nyf63w-315268
> > >
> > >
> > >>
> > >> Signed-off-by: Abhishek Sahu <absahu@xxxxxxxxxxxxxx>
> > >> ---
> > >> drivers/mtd/nand/qcom_nandc.c | 8 ++++++++
> > >> 1 file changed, 8 insertions(+)
> > >>
> > >> diff --git a/drivers/mtd/nand/qcom_nandc.c
> > >> b/drivers/mtd/nand/qcom_nandc.c
> > >> index 563b759..8dd40de 100644
> > >> --- a/drivers/mtd/nand/qcom_nandc.c
> > >> +++ b/drivers/mtd/nand/qcom_nandc.c
> > >> @@ -2334,6 +2334,14 @@ static int qcom_nand_host_setup(struct
> > >> qcom_nand_host *host)
> > >> return -EINVAL;
> > >> }
> > >>
> > >> + /*
> > >> + * Read the required ecc strength from NAND device and overwrite
> > >> + * the device tree ecc strength for devices which require
> > >> + * ecc correctability bits >= 8
> > >> + */
> > >> + if (chip->ecc_strength_ds >= 8)
> > >> + ecc->strength = 8;
> > >> +
> > >> wide_bus = chip->options & NAND_BUSWIDTH_16 ? true : false;
> > >>
> > >> if (ecc->strength >= 8) {
> >
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/
>
>
Thanks,
MiquÃl
--
Miquel Raynal, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com