linux-kernel - Re: [PATCH v4 2/2] mtd: spi-nor: Avoid setting SRWD bit in SR if WP# signal not connected

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Date:   Fri, 30 Jun 2023 16:38:32 +0200
From:   Michael Walle <michael@...le.cc>
To:     Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>
Cc:     tudor.ambarus@...aro.org, pratyush@...nel.org,
        miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, git@....com, linux-mtd@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        amitrkcian2002@...il.com,
        Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>
Subject: Re: [PATCH v4 2/2] mtd: spi-nor: Avoid setting SRWD bit in SR if WP#
 signal not connected

Am 2023-06-30 16:22, schrieb Amit Kumar Mahapatra:
> Setting the status register write disable (SRWD) bit in the status
> register (SR) with WP# signal of the flash left floating or wrongly 
> tied to
> GND (that includes internal pull-downs), will configure the SR 
> permanently
> as read-only. If WP# signal is left floating or wrongly tied to GND, 
> avoid
> setting SRWD bit while writing the SR during flash protection.
> 
> Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>
> ---
>  drivers/mtd/spi-nor/core.c    | 3 +++
>  drivers/mtd/spi-nor/core.h    | 1 +
>  drivers/mtd/spi-nor/debugfs.c | 1 +
>  drivers/mtd/spi-nor/swp.c     | 9 +++++++--
>  4 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 0bb0ad14a2fc..520f5ab86d2b 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -2864,6 +2864,9 @@ static void spi_nor_init_flags(struct spi_nor 
> *nor)
>  	if (flags & NO_CHIP_ERASE)
>  		nor->flags |= SNOR_F_NO_OP_CHIP_ERASE;
> 
> +	if (of_property_read_bool(np, "no-wp"))
> +		nor->flags |= SNOR_F_NO_WP;
> +

Not moved below the first of_property_read_bool() in that function
(as pointed out before). It's just a minor nit.

But with or without that fixed:

Reviewed-by: Michael Walle <michael@...le.cc>

>  	if (flags & SPI_NOR_RWW && nor->info->n_banks > 1 &&
>  	    !nor->controller_ops)
>  		nor->flags |= SNOR_F_RWW;
> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
> index 4fb5ff09c63a..55b5e7abce6e 100644
> --- a/drivers/mtd/spi-nor/core.h
> +++ b/drivers/mtd/spi-nor/core.h
> @@ -132,6 +132,7 @@ enum spi_nor_option_flags {
>  	SNOR_F_SWP_IS_VOLATILE	= BIT(13),
>  	SNOR_F_RWW		= BIT(14),
>  	SNOR_F_ECC		= BIT(15),
> +	SNOR_F_NO_WP		= BIT(16),
>  };
> 
>  struct spi_nor_read_command {
> diff --git a/drivers/mtd/spi-nor/debugfs.c 
> b/drivers/mtd/spi-nor/debugfs.c
> index e11536fffe0f..6e163cb5b478 100644
> --- a/drivers/mtd/spi-nor/debugfs.c
> +++ b/drivers/mtd/spi-nor/debugfs.c
> @@ -27,6 +27,7 @@ static const char *const snor_f_names[] = {
>  	SNOR_F_NAME(SWP_IS_VOLATILE),
>  	SNOR_F_NAME(RWW),
>  	SNOR_F_NAME(ECC),
> +	SNOR_F_NAME(NO_WP),
>  };
>  #undef SNOR_F_NAME
> 
> diff --git a/drivers/mtd/spi-nor/swp.c b/drivers/mtd/spi-nor/swp.c
> index 0ba716e84377..5ab9d5324860 100644
> --- a/drivers/mtd/spi-nor/swp.c
> +++ b/drivers/mtd/spi-nor/swp.c
> @@ -214,8 +214,13 @@ static int spi_nor_sr_lock(struct spi_nor *nor, 
> loff_t ofs, uint64_t len)
> 
>  	status_new = (status_old & ~mask & ~tb_mask) | val;
> 
> -	/* Disallow further writes if WP pin is asserted */
> -	status_new |= SR_SRWD;
> +	/*
> +	 * Disallow further writes if WP# pin is neither left floating nor
> +	 * wrongly tied to GND (that includes internal pull-downs).
> +	 * WP# pin hard strapped to GND can be a valid use case.
> +	 */
> +	if (!(nor->flags & SNOR_F_NO_WP))
> +		status_new |= SR_SRWD;
> 
>  	if (!use_top)
>  		status_new |= tb_mask;