linux-kernel - Re: [PATCH v3 2/6] mtd: rawnand: add an option to specify NAND chip as a boot device

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Date:   Tue, 5 Jun 2018 14:11:02 -0600
From:   Rob Herring <robh@...nel.org>
To:     Stefan Agner <stefan@...er.ch>
Cc:     boris.brezillon@...tlin.com, dwmw2@...radead.org,
        computersforpeace@...il.com, marek.vasut@...il.com,
        mark.rutland@....com, thierry.reding@...il.com, dev@...xeye.de,
        miquel.raynal@...tlin.com, richard@....at, marcel@...wiler.com,
        krzk@...nel.org, digetx@...il.com, benjamin.lindqvist@...ian.se,
        jonathanh@...dia.com, pdeschrijver@...dia.com, pgaikwad@...dia.com,
        mirza.krak@...il.com, linux-mtd@...ts.infradead.org,
        linux-tegra@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/6] mtd: rawnand: add an option to specify NAND chip
 as a boot device

On Fri, Jun 01, 2018 at 12:16:33AM +0200, Stefan Agner wrote:
> Allow to define a NAND chip as a boot device. This can be helpful
> for the selection of the ECC algorithm and strength in case the boot
> ROM supports only a subset of controller provided options.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
>  Documentation/devicetree/bindings/mtd/nand.txt | 4 ++++
>  drivers/mtd/nand/raw/nand_base.c               | 3 +++
>  include/linux/mtd/rawnand.h                    | 6 ++++++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/nand.txt b/Documentation/devicetree/bindings/mtd/nand.txt
> index 8bb11d809429..8daf81b9748c 100644
> --- a/Documentation/devicetree/bindings/mtd/nand.txt
> +++ b/Documentation/devicetree/bindings/mtd/nand.txt
> @@ -43,6 +43,10 @@ Optional NAND chip properties:
>  		     This is particularly useful when only the in-band area is
>  		     used by the upper layers, and you want to make your NAND
>  		     as reliable as possible.
> +- nand-is-boot-medium: Whether the NAND chip is a boot medium. Drivers might use
> +		       this information to select ECC algorithms supported by
> +		       the boot ROM or similar restrictions.
> +

Shouldn't this be a partition level option? You could conceivably do one 
ECC type for boot area and something else for the rest of the NAND.


>  - nand-rb: shall contain the native Ready/Busy ids.
>  
>  The ECC strength and ECC step size properties define the correction capability
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index 9eb5678dd6d0..c8fb7c9855e2 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -5826,6 +5826,9 @@ static int nand_dt_init(struct nand_chip *chip)
>  	if (of_get_nand_bus_width(dn) == 16)
>  		chip->options |= NAND_BUSWIDTH_16;
>  
> +	if (of_property_read_bool(dn, "nand-is-boot-medium"))
> +		chip->options |= NAND_IS_BOOT_MEDIUM;
> +
>  	if (of_get_nand_on_flash_bbt(dn))
>  		chip->bbt_options |= NAND_BBT_USE_FLASH;
>  
> diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
> index 6a82da8c44ce..8e54fcf2fa94 100644
> --- a/include/linux/mtd/rawnand.h
> +++ b/include/linux/mtd/rawnand.h
> @@ -212,6 +212,12 @@ enum nand_ecc_algo {
>   */
>  #define NAND_WAIT_TCCS		0x00200000
>  
> +/*
> + * Whether the NAND chip is a boot medium. Drivers might use this information
> + * to select ECC algorithms supported by the boot ROM or similar restrictions.
> + */
> +#define NAND_IS_BOOT_MEDIUM	0x00400000
> +
>  /* Options set by nand scan */
>  /* Nand scan has allocated controller struct */
>  #define NAND_CONTROLLER_ALLOC	0x80000000
> -- 
> 2.17.0
>