Re: [Qemu-devel] [PATCH] NAND: Correct random data reads.

["andrzej zaborowski" <balrogg@gmail.com>]

2008/12/12 Edgar E. Iglesias <edgar.iglesias@axis.com>:
> I'm having problems with machine that uses a NAND_MFR_STMICRO 0xf1,
> recent Linux versions cannot properly read from the flash.
>
> Turns out that Linux MTD recently learned howto do randomly accessed reads
> from NAND flashes. QEMU has problemns emulating these.
>
> This patch fixes the problem for me but I've only tested on one flash
> model and only with Linux. I'd appreciate help with testing more machines
> with NANDs and ofcourse any comments people may have on the patch.
>
> Thanks
>
> commit 68a19f4348b12f85bd5fbfd8cf7b19033e1fd784
> Author: Edgar E. Iglesias <edgar.iglesias@axis.com>
> Date:   Fri Dec 12 12:48:58 2008 +0100
>
>    NAND: Correct random data reads.
>
>    Random reading depends on having the last row/page latched and not beeing
>    clobbered between read and any following random reads.
>
>    Also, s->iolen must be updated when loading the io/data register with randomly
>    accessed flash data.
>
>    Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
>
> diff --git a/hw/nand.c b/hw/nand.c
> index 7c9f0aa..a6f67c6 100644
> --- a/hw/nand.c
> +++ b/hw/nand.c
> @@ -212,6 +212,7 @@ void nand_reset(struct nand_flash_s *s)
>
>  static void nand_command(struct nand_flash_s *s)
>  {
> +    unsigned int offset;
>     switch (s->cmd) {
>     case NAND_CMD_READ0:
>         s->iolen = 0;
> @@ -233,8 +234,12 @@ static void nand_command(struct nand_flash_s *s)
>     case NAND_CMD_NOSERIALREAD2:
>         if (!(nand_flash_ids[s->chip_id].options & NAND_SAMSUNG_LP))
>             break;
> -
> -        s->blk_load(s, s->addr, s->addr & ((1 << s->addr_shift) - 1));
> +        offset = s->addr & ((1 << s->addr_shift) - 1);
> +        s->blk_load(s, s->addr, offset);
> +        if (s->gnd)
> +            s->iolen = (1 << s->page_shift) - offset;
> +        else
> +            s->iolen = (1 << s->page_shift) + (1 << s->oob_shift) - offset;
>         break;
>
>     case NAND_CMD_RESET:
> @@ -380,12 +385,15 @@ void nand_setio(struct nand_flash_s *s, uint8_t value)
>
>         if (s->cmd != NAND_CMD_RANDOMREAD2) {
>             s->addrlen = 0;
> -            s->addr = 0;
>         }
>     }
>
>     if (s->ale) {
> -        s->addr |= value << (s->addrlen * 8);
> +        unsigned int shift = s->addrlen * 8;
> +        unsigned int mask = ~(0xff << shift);
> +        unsigned int v = value << shift;
> +
> +        s->addr = (s->addr & mask) | v;
>         s->addrlen ++;
>
>         if (s->addrlen == 1 && s->cmd == NAND_CMD_READID)
> @@ -680,9 +688,6 @@ static void glue(nand_blk_load_, PAGE_SIZE)(struct nand_flash_s *s,
>                         offset, PAGE_SIZE + OOB_SIZE - offset);
>         s->ioaddr = s->io;
>     }
> -
> -    s->addr &= PAGE_SIZE - 1;
> -    s->addr += PAGE_SIZE;

Won't that break sequential reading?  I think the other modifications
should also be conditional on the command being RANDOMREAD.

BTW, do you happen to know what the difference is between RANDOMREAD2
and NOSERIALREAD2?  I basically added those commands because various
drivers I found had them declared or some specs had them but there
seems to be no standard or any place where they would be defined.

Cheers