Re: subpage reads/writes with fsl_elbc_nand driver

[Boris Brezillon <bbrezillon@xxxxxxxxxx>]

On Thu, 31 Jan 2019 14:24:15 +0000
Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx> wrote:

> I'm in the process of upgrading a board from an old 3.14-based kernel
> with quite a few out-of-tree patches to one based on 4.19, hopefully
> with much fewer such patches.
> 
> In order to even get the new kernel to mount the existing root
> filesystem, I've had to apply the hacks below:
> 
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -6657,6 +6657,11 @@ static int nand_scan_tail(struct mtd_info *mtd)
>                 pr_warn("WARNING: %s: the ECC used on your system is too
> weak compared to the one required by the NAND chip\n",
>                         mtd->name);
> 
> +       if (IS_ENABLED(CONFIG_ML300PCM31)) {
> +               pr_warn("setting NAND_NO_SUBPAGE_WRITE bit\n");
> +               chip->ecc.write_subpage = NULL;
> +               chip->options |= NAND_NO_SUBPAGE_WRITE;
> +       }
>         /* Allow subpage writes up to ecc.steps. Not possible for MLC
> flash */
>         if (!(chip->options & NAND_NO_SUBPAGE_WRITE) && nand_is_slc(chip)) {
>                 switch (ecc->steps) {
> @@ -6681,8 +6686,12 @@ static int nand_scan_tail(struct mtd_info *mtd)
>         /* Large page NAND with SOFT_ECC should support subpage reads */
>         switch (ecc->mode) {
>         case NAND_ECC_SOFT:
> -               if (chip->page_shift > 9)
> -                       chip->options |= NAND_SUBPAGE_READ;
> +               if (chip->page_shift > 9) {
> +                       if (IS_ENABLED(CONFIG_ML300PCM31))
> +                               pr_warn("setting of NAND_SUBPAGE_READ
> bit has been patched out\n");
> +                       else
> +                               chip->options |= NAND_SUBPAGE_READ;
> +               }
>                 break;
> 
> Without the latter, I get
> 
>     [    0.833134] fsl,elbc-fcm-nand fff00000.nand: fsl_elbc_cmdfunc:
> error, unsupported command 0x5.
>     [    0.841822] fsl,elbc-fcm-nand fff00000.nand: read_buf beyond end
> of buffer (14 requested, 0 available)

For that part of the problem, you should consider converting the driver
to ->exec_op().

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