On Tue, 2009-11-03 at 16:01 +0530, Sudhakar Rajashekhara wrote:
> On TI's DA830/OMAP-L137, DA850/OMAP-L138 and DM365, after
> setting the 4BITECC_ADD_CALC_START bit in the NAND Flash
> control register to 1 and before waiting for the NAND Flash
> status register to be equal to 1, 2 or 3, we have to wait
> till the ECC HW goes to correction state. Without this wait,
> ECC correction calculations will not be proper.
>
> This has been tested on DA830/OMAP-L137, DA850/OMAP-L138,
> DM355 and DM365 EVMs.
>
> Signed-off-by: Sudhakar Rajashekhara <[email protected]>
> Acked-by: Sneha Narnakaje <[email protected]>
> ---
> drivers/mtd/nand/davinci_nand.c | 16 ++++++++++++++++
> 1 files changed, 16 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
> index fe3eba8..8a32999 100644
> --- a/drivers/mtd/nand/davinci_nand.c
> +++ b/drivers/mtd/nand/davinci_nand.c
> @@ -310,6 +310,7 @@ static int nand_davinci_correct_4bit(struct mtd_info *mtd,
> unsigned short ecc10[8];
> unsigned short *ecc16;
> u32 syndrome[4];
> + u32 ecc_state;
> unsigned num_errors, corrected;
>
> /* All bytes 0xff? It's an erased page; ignore its ECC. */
> @@ -360,6 +361,21 @@ compare:
> */
> davinci_nand_writel(info, NANDFCR_OFFSET,
> davinci_nand_readl(info, NANDFCR_OFFSET) | BIT(13));
> +
> + /*
> + * ECC_STATE field reads 0x3 (Error correction complete) immediately
> + * after setting the 4BITECC_ADD_CALC_START bit. So if you immediately
> + * begin trying to poll for the state, you may fall right out of your
> + * loop without any of the correction calculations having taken place.
> + * The recommendation from the hardware team is to wait till ECC_STATE
> + * reads less than 4, which means ECC HW has entered correction state.
> + */
> + do {
> + ecc_state = (davinci_nand_readl(info,
> + NANDFSR_OFFSET) >> 8) & 0x0f;
> + cpu_relax();
> + } while (ecc_state < 4);
> +
> for (;;) {
> u32 fsr = davinci_nand_readl(info, NANDFSR_OFFSET);
I see a lot of constructs like this in many mtd drivers. I wonder, what
happens if ecc_state never becomes < 4? Should there be some protection
against this, e.g., exit the loop with an error message if we are
looping for more than 1 or several seconds?
What is the "official" / "right" way for this kind of loops?
--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)