linux-kernel - Re: [PATCH v2 2/3] mtd: spi-nor: add support to unlock flash device.

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Message-ID: <alpine.DEB.2.21.9999.1904301016400.7063@viisi.sifive.com>
Date:   Tue, 30 Apr 2019 10:19:10 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Sagar Shrikant Kadam <sagar.kadam@...ive.com>
cc:     marek.vasut@...il.com, tudor.ambarus@...rochip.com,
        dwmw2@...radead.org, computersforpeace@...il.com,
        bbrezillon@...nel.org, richard@....at, palmer@...ive.com,
        paul.walmsley@...ive.com, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 2/3] mtd: spi-nor: add support to unlock flash
 device.

On Sun, 28 Apr 2019, Sagar Shrikant Kadam wrote:

> Nor device (is25wp256 mounted on HiFive unleashed Rev A00 board) from ISSI
> have memory blocks guarded by block protection bits BP[0,1,2,3].
> 
> Clearing block protection bits,unlocks the flash memory regions
> The unlock scheme is registered during nor scans.

This also looks like it's partially based on Wes or Palmer's patch from 

https://github.com/riscv/riscv-linux/commit/c94e267766d62bc9a669611c3d0c8ed5ea26569b

Please note that in the patch message.

> Signed-off-by: Sagar Shrikant Kadam <sagar.kadam@...ive.com>
> ---
>  drivers/mtd/spi-nor/spi-nor.c | 48 ++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/mtd/spi-nor.h   |  1 +
>  2 files changed, 48 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index c5408ed..81c7b3e 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -1461,6 +1461,46 @@ static int macronix_quad_enable(struct spi_nor *nor)
>  }
>  
>  /**
> + * issi_unlock() - clear BP[0123] write-protection.
> + * @nor: pointer to a 'struct spi_nor'
> + * @ofs: offset from which to unlock memory
> + * @len: number of bytes to unlock
> + * Bits [2345] of the Status Register are BP[0123].
> + * ISSI chips use a different block protection scheme than other chips.
> + * Just disable the write-protect unilaterally.
> + * Return: 0 on success, -errno otherwise.

This is closer to kernel-doc format, but not quite.  Please update this to 
align to

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/doc-guide/kernel-doc.rst#n57


- Paul

> + */
> +static int issi_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)
> +{
> +	int ret, val;
> +	u8 mask = SR_BP0 | SR_BP1 | SR_BP2 | SR_BP3;
> +
> +	val = read_sr(nor);
> +	if (val < 0)
> +		return val;
> +	if (!(val & mask))
> +		return 0;
> +
> +	write_enable(nor);
> +
> +	write_sr(nor, val & ~mask);
> +
> +	ret = spi_nor_wait_till_ready(nor);
> +	if (ret)
> +		return ret;
> +
> +	ret = read_sr(nor);
> +	if (ret > 0 && !(ret & mask)) {
> +		dev_info(nor->dev,
> +			"ISSI Block Protection Bits cleared SR=0x%x", ret);
> +		return 0;
> +	} else {
> +		dev_err(nor->dev, "ISSI Block Protection Bits not cleared\n");
> +		return -EINVAL;
> +	}
> +}
> +
> +/**
>   * spansion_quad_enable() - set QE bit in Configuraiton Register.
>   * @nor:	pointer to a 'struct spi_nor'
>   *
> @@ -1836,7 +1876,7 @@ static int sr2_bit7_quad_enable(struct spi_nor *nor)
>  			SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ) },
>  	{ "is25wp256", INFO(0x9d7019, 0, 64 * 1024, 1024,
>  			SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ |
> -			SPI_NOR_4B_OPCODES)
> +			SPI_NOR_4B_OPCODES | SPI_NOR_HAS_LOCK)
>  	},
>  
>  	/* Macronix */
> @@ -4078,6 +4118,12 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
>  		nor->flash_is_locked = stm_is_locked;
>  	}
>  
> +	/* NOR protection support for ISSI chips */
> +	if (JEDEC_MFR(info) == SNOR_MFR_ISSI ||
> +	    info->flags & SPI_NOR_HAS_LOCK) {
> +		nor->flash_unlock = issi_unlock;
> +
> +	}
>  	if (nor->flash_lock && nor->flash_unlock && nor->flash_is_locked) {
>  		mtd->_lock = spi_nor_lock;
>  		mtd->_unlock = spi_nor_unlock;
> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
> index ff13297..9a7d719 100644
> --- a/include/linux/mtd/spi-nor.h
> +++ b/include/linux/mtd/spi-nor.h
> @@ -127,6 +127,7 @@
>  #define SR_BP0			BIT(2)	/* Block protect 0 */
>  #define SR_BP1			BIT(3)	/* Block protect 1 */
>  #define SR_BP2			BIT(4)	/* Block protect 2 */
> +#define SR_BP3			BIT(5)	/* Block protect 3 for ISSI device*/
>  #define SR_TB			BIT(5)	/* Top/Bottom protect */
>  #define SR_SRWD			BIT(7)	/* SR write protect */
>  /* Spansion/Cypress specific status bits */
> -- 
> 1.9.1
> 
>