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SubjectRe: [PATCH v2] mtd: rawnand: denali: do not pass zero maxchips to nand_scan()
Hi Masahiro,

Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Mon, 27 Aug
2018 16:01:41 +0900:

> Commit 49aa76b16676 ("mtd: rawnand: do not execute nand_scan_ident()
> if maxchips is zero") gave a new meaning for calling nand_scan_ident()
> with maxchips=0.
>
> It is a special usage for some drivers such as docg4, but actually
> the Denali driver may pass maxchips=0 to nand_scan() when the driver
> is enabled but no NAND chip is found on the board for some reasons.
>
> If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident()
> is skipped, then nand_set_defaults() is skipped as well. Thus, the
> driver must set chip->controller beforehand. Otherwise, nand_attach()
> causes NULL pointer dereference.
>
> In fact, the Denali controller knows the number of connected chips
> before calling nand_scan_ident(); if DEVICE_RESET fails, there is no
> chip in that chip select. Then, denali_reset_banks() sets the maxchips
> to the number of detected chips. If no chip is found, maxchips is zero.
>
> In this case, there is no point for calling nand_scan() because we know
> it will fail for sure. Let's make the probe function fail immediately.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
>
> Changes in v2:
> - Return -ENODEV immediately if no chip was found on the board
> for some reasons.
> This is the smallest, and safest change for the fixes branch.
> (I will investigate later if further cleanups are possible or not.)
>
> drivers/mtd/nand/raw/denali.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c
> index ca18612..67b2065 100644
> --- a/drivers/mtd/nand/raw/denali.c
> +++ b/drivers/mtd/nand/raw/denali.c
> @@ -1338,6 +1338,11 @@ int denali_init(struct denali_nand_info *denali)
>
> denali_enable_irq(denali);
> denali_reset_banks(denali);
> + if (!denali->max_banks) {
> + /* Error out earlier if no chip is found for some reasons. */
> + ret = -ENODEV;
> + goto disable_irq;
> + }
>
> denali->active_bank = DENALI_INVALID_BANK;
>

Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>

Boris, This is for you :)

Thanks,
Miquèl

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