Re: [PATCH v2 1/2] mtd: spi-nor: add Global Block Unlock support

[Boris Brezillon <boris.brezillon@collabora.com>]

On Sat, 24 Aug 2019 12:27:12 +0000
<Tudor.Ambarus@microchip.com> wrote:

> From: Tudor Ambarus <tudor.ambarus@microchip.com>
> 
> To avoid inadvertent writes during power-up, some flashes are
> write-protected by default after a power-on reset cycle.
> A Global Block-Protection Unlock command offers a single
> command cycle that unlocks the entire memory array. This is
> identical with what other nor flashes are doing by clearing
> the block protection bits from the status register: disable
> the write protection after a power-on reset cycle.
> 
> We can't determine this purely by manufacturer type and it's not
> autodetectable by anything like SFDP, so make a new flag for it:
> UNLOCK_GLOBAL_BLOCK.
> 
> Note that the Global Block Unlock command has different names
> depending on the manufacturer, but always the same command value:
> 0x98. Macronix's MX25U12835F names it Gang Block Unlock,
> Winbound's W25Q128FV names it Global Block Unlock and
> Microchip's SST26VF064B names it Global Block Protection Unlock.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
> ---
> v2: the check for UNLOCK_GLOBAL_BLOCK should be done the first
> thing in spi_nor_disable_block_protection(). We use it for a faster
> throughput, a single command cycle that unlocks the entire memory
> array. Fix it.
> 
>  drivers/mtd/spi-nor/spi-nor.c | 46 ++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/mtd/spi-nor.h   |  1 +
>  2 files changed, 46 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 1896d36a7d11..c0ba6fe62461 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -196,7 +196,7 @@ struct flash_info {
>  	u16		page_size;
>  	u16		addr_width;
>  
> -	u16		flags;
> +	u32		flags;
>  #define SECT_4K			BIT(0)	/* SPINOR_OP_BE_4K works uniformly */
>  #define SPI_NOR_NO_ERASE	BIT(1)	/* No erase command needed */
>  #define SST_WRITE		BIT(2)	/* use SST byte programming */
> @@ -233,6 +233,7 @@ struct flash_info {
>  #define SPI_NOR_SKIP_SFDP	BIT(13)	/* Skip parsing of SFDP tables */
>  #define USE_CLSR		BIT(14)	/* use CLSR command */
>  #define SPI_NOR_OCTAL_READ	BIT(15)	/* Flash supports Octal Read */
> +#define UNLOCK_GLOBAL_BLOCK	BIT(16)	/* Unlock global block protection */

Let's add the corresponding SNOR_F_ flag so that manufacturer/sfdp init
can set the flag directly.

>  
>  	/* Part specific fixup hooks. */
>  	const struct spi_nor_fixups *fixups;
> @@ -2031,6 +2032,41 @@ static int spi_nor_spansion_clear_sr_bp(struct spi_nor *nor)
>  	return spi_nor_clear_sr_bp(nor);
>  }
>  
> +/**
> + * spi_nor_unlock_global_block_protection() - Unlock the Global Block Protection
> + * @nor:        pointer to a 'struct spi_nor'
> + *
> + * The Global Block-Protection Unlock command offers a single command cycle
> + * that unlocks the entire memory array.
> + *
> + * Return: 0 on success, -errno otherwise.
> + */
> +static int spi_nor_unlock_global_block_protection(struct spi_nor *nor)
> +{
> +	int ret;
> +
> +	write_enable(nor);
> +
> +	if (nor->spimem) {
> +		struct spi_mem_op op =
> +			SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_ULBPR, 1),
> +				   SPI_MEM_OP_NO_ADDR,
> +				   SPI_MEM_OP_NO_DUMMY,
> +				   SPI_MEM_OP_NO_DATA);
> +
> +		ret = spi_mem_exec_op(nor->spimem, &op);
> +	} else {
> +		ret = nor->write_reg(nor, SPINOR_OP_ULBPR, NULL, 0);
> +	}
> +
> +	if (ret < 0) {
> +		dev_err(nor->dev, "error %d on ULBPR\n", ret);
> +		return ret;
> +	}
> +
> +	return spi_nor_wait_till_ready(nor);
> +}
> +
>  /* Used when the "_ext_id" is two bytes at most */
>  #define INFO(_jedec_id, _ext_id, _sector_size, _n_sectors, _flags)	\
>  		.id = {							\
> @@ -4697,6 +4733,14 @@ static int spi_nor_quad_enable(struct spi_nor *nor)
>   */
>  static int spi_nor_disable_block_protection(struct spi_nor *nor)
>  {
> +	/*
> +	 * If the flash supports the Global Block-Protection Unlock command,
> +	 * use it for faster throughput: a single command cycle that unlocks
> +	 * the entire memory array.
> +	 */
> +	if (nor->info->flags & UNLOCK_GLOBAL_BLOCK)
> +		return spi_nor_unlock_global_block_protection(nor);

Hm, I'd rather put that as a new hook in spi_nor_locking_ops, this way
we're ready to support any vendor-specific variant (and I like the idea
of having all locking-related functions placed in a separate _ops
struct).

> +
>  	if (!nor->params.disable_block_protection)
>  		return 0;
>  
> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
> index 4752d08e9a3e..31b99a7743fc 100644
> --- a/include/linux/mtd/spi-nor.h
> +++ b/include/linux/mtd/spi-nor.h
> @@ -66,6 +66,7 @@
>  #define SPINOR_OP_CLFSR		0x50	/* Clear flag status register */
>  #define SPINOR_OP_RDEAR		0xc8	/* Read Extended Address Register */
>  #define SPINOR_OP_WREAR		0xc5	/* Write Extended Address Register */
> +#define SPINOR_OP_ULBPR		0x98	/* Global Block Unlock Protection */
>  
>  /* 4-byte address opcodes - used on Spansion and some Macronix flashes. */
>  #define SPINOR_OP_READ_4B	0x13	/* Read data bytes (low frequency) */