Hi,
On Tuesday 05 of November 2013 12:07:29 Brian Norris wrote:
> On Mon, Oct 28, 2013 at 11:05:17AM +0800, Huang Shijie wrote:
> > In default way, we use the ecc_strength/ecc_step size calculated by ourselves
> > and use all the OOB area.
> >
> > This patch adds a new property : "fsl,use-minimum-ecc"
> >
> > If we enable it, we will firstly try to use the datasheet's minimum required
> > ECC provided by the MTD layer (the ecc_strength_ds/ecc_step_ds fields
> > in the nand_chip{}). So we may have free space in the OOB area by using the
> > minimum ECC, and we may support JFFS2 with some SLC NANDs, such as Micron's
> > SLC NAND.
> >
> > If we fail to use the minimum ECC, we will use the legacy method to calculate
> > the ecc_strength and ecc_step size.
> >
> > Signed-off-by: Huang Shijie <b32955@xxxxxxxxxxxxx>
> > ---
> > v1 --> v2:
> > based on David's patch to fix the regression.
> > ---
> > .../devicetree/bindings/mtd/gpmi-nand.txt | 6 ++++++
> > drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 3 +++
> > 2 files changed, 9 insertions(+), 0 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/mtd/gpmi-nand.txt b/Documentation/devicetree/bindings/mtd/gpmi-nand.txt
> > index 551b2a1..4297795 100644
> > --- a/Documentation/devicetree/bindings/mtd/gpmi-nand.txt
> > +++ b/Documentation/devicetree/bindings/mtd/gpmi-nand.txt
> > @@ -17,6 +17,12 @@ Required properties:
> > Optional properties:
> > - nand-on-flash-bbt: boolean to enable on flash bbt option if not
> > present false
> > + - fsl,use-minimum-ecc: By enabling this boolean property, the gpmi will try
> > + to use the datasheet's minimum required ECC provided by
> > + the MTD layer (the ecc_strength_ds/ecc_step_ds fields
> > + in the nand_chip{}). So we may have free space in the OOB
> > + area by using the minimum ECC, and we may support JFFS2
> > + with some SLC NANDs, such as Micron's SLC NAND.
>
> This description still uses Linux-isms/MTD-isms (ecc_strength_ds,
> ecc_step_ds, nand_chip{}, JFFS2). I would personally write this as
> something like the following:
>
> - fsl,use-minimum-ecc: Protect this NAND flash with the minimum ECC
> strength required. The required ECC strength is
> automatically discoverable for some flash
> (e.g., according to the ONFI standard).
> However, note that if this strength is not
> discoverable, the software may choose an
> implementation-defined ECC scheme.
After reading this description, it is not clear to me what is the default
behavior if this property is not present.
Best regards,
Tomasz
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