linux-kernel - Re: [PATCH v2] mtd: rawnand: denali: set SPARE_AREA_SKIP

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Date:   Tue, 2 Oct 2018 14:28:33 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mtd@...ts.infradead.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-kernel@...r.kernel.org, Dinh Nguyen <dinguyen@...nel.org>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2] mtd: rawnand: denali: set SPARE_AREA_SKIP_BYTES
 register to 8 if unset

On Fri, 28 Sep 2018 13:16:01 +0900
Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:

> NAND devices need additional data area (OOB) for error correction,
> but it is also used for Bad Block Marker (BBM).  In many cases, the
> first byte in OOB is used for BBM, but the location actually depends
> on chip vendors.  The NAND controller should preserve the precious
> BBM to keep track of bad blocks.
> 
> In Denali IP, the SPARE_AREA_SKIP_BYTES register is used to specify
> the number of bytes to skip from the start of OOB.  The ECC engine
> will automatically skip the specified number of bytes when it gets
> access to OOB area.
> 
> The same value for SPARE_AREA_SKIP_BYTES should be used between
> firmware and the operating system if you intend to use the NAND
> device across the control hand-off.
> 
> In fact, the current denali.c code expects firmware to have already
> set the SPARE_AREA_SKIP_BYTES register, then reads the value out.
> 
> If no firmware (or bootloader) has initialized the controller, the
> register value is zero, which is the default after power-on-reset.
> In other words, the Linux driver cannot initialize the controller
> by itself.
> 
> Some possible solutions are:
> 
>  [1] Add a DT property to specify the skipped bytes in OOB
>  [2] Associate the preferred value with compatible
>  [3] Hard-code the default value in the driver
> 
> My first attempt was [1], but in the review process, [3] was suggested
> as a counter-implementation.
> (https://lore.kernel.org/patchwork/patch/983055/)
> 
> The default value 8 was chosen to match to the boot ROM of the UniPhier
> platform.  The preferred value may vary by platform.  If so, please
> trade up to a different solution.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Reviewed-by: Boris Brezillon <boris.brezillon@...tlin.com>

> ---
> 
> Changes in v2:
>   - Change approach from a DT-property to a hard-coded dafault
> 
>  drivers/mtd/nand/raw/denali.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c
> index aaab121..18bbfc8 100644
> --- a/drivers/mtd/nand/raw/denali.c
> +++ b/drivers/mtd/nand/raw/denali.c
> @@ -21,6 +21,7 @@
>  #include "denali.h"
>  
>  #define DENALI_NAND_NAME    "denali-nand"
> +#define DENALI_DEFAULT_OOB_SKIP_BYTES	8
>  
>  /* for Indexed Addressing */
>  #define DENALI_INDEXED_CTRL	0x00
> @@ -1056,12 +1057,17 @@ static void denali_hw_init(struct denali_nand_info *denali)
>  		denali->revision = swab16(ioread32(denali->reg + REVISION));
>  
>  	/*
> -	 * tell driver how many bit controller will skip before
> -	 * writing ECC code in OOB, this register may be already
> -	 * set by firmware. So we read this value out.
> -	 * if this value is 0, just let it be.
> +	 * Set how many bytes should be skipped before writing data in OOB.
> +	 * If a non-zero value has already been set (by firmware or something),
> +	 * just use it.  Otherwise, set the driver default.
>  	 */
>  	denali->oob_skip_bytes = ioread32(denali->reg + SPARE_AREA_SKIP_BYTES);
> +	if (!denali->oob_skip_bytes) {
> +		denali->oob_skip_bytes = DENALI_DEFAULT_OOB_SKIP_BYTES;
> +		iowrite32(denali->oob_skip_bytes,
> +			  denali->reg + SPARE_AREA_SKIP_BYTES);
> +	}
> +
>  	denali_detect_max_banks(denali);
>  	iowrite32(0x0F, denali->reg + RB_PIN_ENABLED);
>  	iowrite32(CHIP_EN_DONT_CARE__FLAG, denali->reg + CHIP_ENABLE_DONT_CARE);