linux-kernel - Re: [PATCH 2/2] mtd: nand: gpmi: add support for specific ECC strength

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Date:   Wed, 14 Feb 2018 20:05:37 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Han Xu <han.xu@....com>
Cc:     Stefan Agner <stefan@...er.ch>,
        "boris.brezillon@...e-electrons.com" 
        <boris.brezillon@...e-electrons.com>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "richard@....at" <richard@....at>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "cyrille.pitchen@...ev4u.fr" <cyrille.pitchen@...ev4u.fr>,
        "max.oss.09@...il.com" <max.oss.09@...il.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mtd: nand: gpmi: add support for specific ECC
 strength

On Wed, 14 Feb 2018 16:28:36 +0000
Han Xu <han.xu@....com> wrote:

> On 02/06/2018 11:40 AM, Stefan Agner wrote:
> > Add support for specified ECC strength/size using device tree
> > properties nand-ecc-strength/nand-ecc-step-size.
> >
> > Signed-off-by: Stefan Agner <stefan@...er.ch>
> > ---
> >   .../devicetree/bindings/mtd/gpmi-nand.txt          |  5 ++++
> >   drivers/mtd/nand/gpmi-nand/gpmi-nand.c             | 29 ++++++++++++++--------
> >   2 files changed, 24 insertions(+), 10 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/mtd/gpmi-nand.txt b/Documentation/devicetree/bindings/mtd/gpmi-nand.txt
> > index eb2d9919d063..ea6e9b735160 100644
> > --- a/Documentation/devicetree/bindings/mtd/gpmi-nand.txt
> > +++ b/Documentation/devicetree/bindings/mtd/gpmi-nand.txt
> > @@ -46,6 +46,11 @@ Optional properties:
> >                          partitions written from Linux with this feature
> >                          turned on may not be accessible by the BootROM
> >                          code.
> > +  - nand-ecc-strength: integer representing the number of bits to correct
> > +                       per ECC step. Needs to be a multiple of 2.
> > +  - nand-ecc-step-size: integer representing the number of data bytes
> > +                       that are covered by a single ECC step. The driver
> > +                       supports 512 and 1024.
> >   
> >   The device tree may optionally contain sub-nodes describing partitions of the
> >   address space. See partition.txt for more detail.
> > diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> > index 50f8d4a1b983..8cb378358e11 100644
> > --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> > +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> > @@ -198,17 +198,15 @@ static inline bool gpmi_check_ecc(struct gpmi_nand_data *this)
> >    *
> >    * We may have available oob space in this case.
> >    */
> > -static int set_geometry_by_ecc_info(struct gpmi_nand_data *this)
> > +static int set_geometry_by_ecc_info(struct gpmi_nand_data *this,
> > +			unsigned int ecc_strength, unsigned int ecc_step)
> >   {
> >   	struct bch_geometry *geo = &this->bch_geometry;
> >   	struct nand_chip *chip = &this->nand;
> >   	struct mtd_info *mtd = nand_to_mtd(chip);
> >   	unsigned int block_mark_bit_offset;
> >   
> > -	if (!(chip->ecc_strength_ds > 0 && chip->ecc_step_ds > 0))
> > -		return -EINVAL;
> > -
> > -	switch (chip->ecc_step_ds) {
> > +	switch (ecc_step) {
> >   	case SZ_512:
> >   		geo->gf_len = 13;
> >   		break;
> > @@ -221,8 +219,8 @@ static int set_geometry_by_ecc_info(struct gpmi_nand_data *this)
> >   			chip->ecc_strength_ds, chip->ecc_step_ds);
> >   		return -EINVAL;
> >   	}
> > -	geo->ecc_chunk_size = chip->ecc_step_ds;
> > -	geo->ecc_strength = round_up(chip->ecc_strength_ds, 2);
> > +	geo->ecc_chunk_size = ecc_step;
> > +	geo->ecc_strength = round_up(ecc_strength, 2);
> >   	if (!gpmi_check_ecc(this))
> >   		return -EINVAL;
> >   
> > @@ -230,7 +228,7 @@ static int set_geometry_by_ecc_info(struct gpmi_nand_data *this)
> >   	if (geo->ecc_chunk_size < mtd->oobsize) {
> >   		dev_err(this->dev,
> >   			"unsupported nand chip. ecc size: %d, oob size : %d\n",
> > -			chip->ecc_step_ds, mtd->oobsize);
> > +			ecc_step, mtd->oobsize);
> >   		return -EINVAL;
> >   	}
> >   
> > @@ -423,9 +421,20 @@ static int legacy_set_geometry(struct gpmi_nand_data *this)
> >   
> >   int common_nfc_set_geometry(struct gpmi_nand_data *this)
> >   {
> > +	struct nand_chip *chip = &this->nand;
> > +
> > +	if (chip->ecc.strength > 0 && chip->ecc.size > 0)
> > +		return set_geometry_by_ecc_info(this, chip->ecc.strength,
> > +						chip->ecc.size);
> > +  
> 
> I was wondering how to keep, let's say u-boot, and kernel ecc setting 
> aligned, if users can specify the strength and step_ds in DT? Did u-boot 
> enable to get these parameters from DT?

Both u-boot and Linux have to support using strength/step information
passed through the DT before you can start patching dts files. Anyway,
users will have to change their DT (add the nand-ecc-strength/step-size
properties) to use this feature, so they should quickly notice that
something is going wrong and update their bootloader or drop those
nand-ecc-xxx props.

> >   	if ((of_property_read_bool(this->dev->of_node, "fsl,use-minimum-ecc"))
> > -				|| legacy_set_geometry(this))
> > -		return set_geometry_by_ecc_info(this);
> > +				|| legacy_set_geometry(this)) {
> > +		if (!(chip->ecc_strength_ds > 0 && chip->ecc_step_ds > 0))
> > +			return -EINVAL;
> > +
> > +		return set_geometry_by_ecc_info(this, chip->ecc_strength_ds,
> > +						chip->ecc_step_ds);
> > +	}
> >   
> >   	return 0;
> >   }  



-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com