[U-Boot] [PATCH] NAND: DaVinci: Update 4 bit ECC correction

[Paulraj, Sandeep]

> > From: Sandeep Paulraj <s-paulraj at ti.com>
> >
> > There was a bug in the 4 bit ECC calculation routine
> > in the DaVinci NAND driver. This becomes prominent
> > when we use 4K page size NAND devices.
> > This is a fix for the issue.
> >
> > Signed-off-by: Sandeep Paulraj <s-paulraj at ti.com>
> > ---
> >  drivers/mtd/nand/davinci_nand.c |   11 +++++++++++
> >  1 files changed, 11 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/mtd/nand/davinci_nand.c
> b/drivers/mtd/nand/davinci_nand.c
> > index 41a9568..68a0e15 100644
> > --- a/drivers/mtd/nand/davinci_nand.c
> > +++ b/drivers/mtd/nand/davinci_nand.c
> > @@ -388,6 +388,17 @@ static int nand_davinci_4bit_correct_data(struct
> mtd_info *mtd, uint8_t *dat,
> >  	emif_regs->NANDFCR |= 1 << 13;
> >
> >  	/*
> > +	 * ECC_STATE in NANDFSR register reads 0x3 (Error correction
> complete)
> > +	 * immediately after setting the 4BITECC_ADD_CALC_START bit. So if
> we
> > +	 * begin trying to poll for the state, we may fall right out of your
> > +	 * loop
> 
> "your" loop?
> 
> >  without any of the correction calculations having taken place.
> > +	 * So wait till ECC_STATE reads less than 4.
> > +	 */
> > +	do {
> > +		val = ((emif_regs->NANDFSR >> 8) & 0xf);
> > +	} while (val < 4);
> 
> Comment says wait until less than 4, code says wait until at least 4.
> Could
> symbolic constants be used to describe the states instead of magic numbers
> like 4 and 0xc00?
I'll update my explanations and use symbolic constants

> 
> Is it possible that there could be a race, whereby the hardware finishes
> before you read NANDFSR for the first time, and thus you never see it be
> greater than 3?

There are other check conditions after this check condition in the driver.
If we never see the concetned value greater than 3, that actually means that ECC calculation has finished or not required at all because there were no errors

> 
> -Scott