Re: [PATCH v2 4/4] mtd: core: Fix a conflict between MTD and NVMEM on wp-gpios property

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Vignesh, Tudory, Pratyush,

+ Tudor and Pratyush

christophe.kerello@foss.st.com wrote on Mon, 31 Jan 2022 10:57:55 +0100:

> Wp-gpios property can be used on NVMEM nodes and the same property can
> be also used on MTD NAND nodes. In case of the wp-gpios property is
> defined at NAND level node, the GPIO management is done at NAND driver
> level. Write protect is disabled when the driver is probed or resumed
> and is enabled when the driver is released or suspended.
> 
> When no partitions are defined in the NAND DT node, then the NAND DT node
> will be passed to NVMEM framework. If wp-gpios property is defined in
> this node, the GPIO resource is taken twice and the NAND controller
> driver fails to probe.
> 
> A new Boolean flag named skip_wp_gpio has been added in nvmem_config.
> In case skip_wp_gpio is set, it means that the GPIO is handled by the
> provider. Lets set this flag in MTD layer to avoid the conflict on
> wp_gpios property.
> 
> Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
> ---
>  drivers/mtd/mtdcore.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 70f492dce158..e6d251594def 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -546,6 +546,7 @@ static int mtd_nvmem_add(struct mtd_info *mtd)
>  	config.stride = 1;
>  	config.read_only = true;
>  	config.root_only = true;
> +	config.skip_wp_gpio = true;
>  	config.no_of_node = !of_device_is_compatible(node, "nvmem-cells");
>  	config.priv = mtd;
>  
> @@ -833,6 +834,7 @@ static struct nvmem_device *mtd_otp_nvmem_register(struct mtd_info *mtd,
>  	config.owner = THIS_MODULE;
>  	config.type = NVMEM_TYPE_OTP;
>  	config.root_only = true;
> +	config.skip_wp_gpio = true;
>  	config.reg_read = reg_read;
>  	config.size = size;
>  	config.of_node = np;

TLDR: There is a conflict between MTD and NVMEM, who should handle the
WP pin when there is one? At least for raw NAND devices, I don't want
the NVMEM core to handle the wp pin. So we've introduced this
skip_wp_gpio nvmem config option. But there are two places where this
boolean can be set and one of these is for otp regions (see above). In
this case, I don't know if it is safe or if CFI/SPI-NOR rely on the
nvmem protection. Please tell us if you think this is fine for you.

Thanks,
Miquèl