linux-kernel - Re: [PATCH] Fix writing mtdoops to nand flash.

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Date:   Mon, 30 Oct 2017 09:23:03 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     motobud@...il.com
Cc:     Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix writing mtdoops to nand flash.

Hi Brent,

Subject should be prefixed by "mtd: nand: ", so

"mtd: nand: Fix writing mtdoops to nand flash"

On Sun, 29 Oct 2017 23:23:43 -0500
motobud@...il.com wrote:

> From: Brent Taylor <motobud@...il.com>
> 
> When mtdoops calls mtd_panic_write, it eventually calls
> panic_nand_write in nand_base.c.  In order to properly
> wait for the nand chip to be ready in panic_nand_wait,
> the chip must first be selected.
> 
> When using the atmel nand flash controller, a panic
> would occur due to a NULL pointer exception.
> 
> Signed-off-by: Brent Taylor <motobud@...il.com>
> ---
>  drivers/mtd/nand/nand_base.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index 12edaae17d81..0a8058a66d93 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -2802,9 +2802,14 @@ static int panic_nand_write(struct mtd_info *mtd, loff_t to, size_t len,
>  	struct mtd_oob_ops ops;
>  	int ret;
>  
> +	int chipnr = (int)(to >> chip->chip_shift);
> +	chip->select_chip(mtd, chipnr);
> +
>  	/* Wait for the device to get ready */
>  	panic_nand_wait(mtd, chip, 400);
>  
> +	chip->select_chip(mtd, -1);
> +

Duh! Looks like a piece of code that is never tested. Did you face the
problem or did you find out by inspecting the code?

Anyway, I fear the atmel driver is not the only one to rely on the chip
to be selected when ->dev_ready() is called so this should definitely
be fixed. Also, we should probably move the ->select_chip() and
panic_nand_wait() calls after panic_nand_get_device(), and I don't
think we need to unselect the chip (it will be taken care of by
nand_do_write_ops()).

>  	/* Grab the device */
>  	panic_nand_get_device(chip, mtd, FL_WRITING);
>