Re: [PATCH 2/2] mtd: spi-nor: add a stateless method to support memory size above 128Mib

[Marek Vasut <marek.vasut@gmail.com>]

On 12/06/2016 05:52 PM, Cyrille Pitchen wrote:
> This patch provides an alternative mean to support memory above 16MiB
> (128Mib) by replacing 3byte address op codes by their associated 4byte
> address versions.
> 
> Using the dedicated 4byte address op codes doesn't change the internal
> state of the SPI NOR memory as opposed to using other means such as
> updating a Base Address Register (BAR) and sending command to enter/leave
> the 4byte mode.
> 
> Hence when a CPU reset occurs, early bootloaders don't need to be aware
> of BAR value or 4byte mode being enabled: they can still access the first
> 16MiB of the SPI NOR memory using the regular 3byte address op codes.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
> Tested-by: Vignesh R <vigneshr@ti.com>
> ---
>  drivers/mtd/spi-nor/spi-nor.c | 114 ++++++++++++++++++++++++++++++++++--------
>  1 file changed, 93 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 8abe134e174a..606c030c566d 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -75,6 +75,10 @@ struct flash_info {
>  					 * bit. Must be used with
>  					 * SPI_NOR_HAS_LOCK.
>  					 */
> +#define SPI_NOR_4B_OPCODES	BIT(10)	/*
> +					 * Use dedicated 4byte address op codes
> +					 * to support memory size above 128Mib.
> +					 */
>  };
>  
>  #define JEDEC_MFR(info)	((info)->id[0])
> @@ -188,6 +192,91 @@ static inline struct spi_nor *mtd_to_spi_nor(struct mtd_info *mtd)
>  	return mtd->priv;
>  }
>  
> +
> +struct spi_nor_address_entry {
> +	u8	src_opcode;
> +	u8	dst_opcode;
> +};
> +
> +static u8 spi_nor_convert_opcode(u8 opcode,
> +				 const struct spi_nor_address_entry *entries,
> +				 size_t num_entries)
> +{
> +	int min, max;
> +
> +	/*
> +	 * This function implements a dichotomic search in the entries[]
> +	 * array indexed by src_opcode. Hence we assume that the entries[]
> +	 * array is sorted by src_opcode.
> +	 * The dichotomic search has a logarithmic complexity as opposed
> +	 * to a simple loop on all entires, which has a linear complexity:
> +	 * it means that when n is the number of entries in the input array,
> +	 * the dichotomic search performs O(log2(n)) comparisons whereas
> +	 * a simple loop performs O(n) comparisons.
> +	 */
> +	min = 0;
> +	max = num_entries - 1;
> +	while (min <= max) {
> +		int mid = (min + max) >> 1;
> +		const struct spi_nor_address_entry *entry = &entries[mid];
> +
> +		if (opcode == entry->src_opcode)
> +			return entry->dst_opcode;
> +
> +		if (opcode < entry->src_opcode)
> +			max = mid - 1;
> +		else
> +			min = mid + 1;
> +	}

You have like 16 entries in that table, just do a linear search, this is
only complex for no benefit.

> +	/* No conversion found */
> +	return opcode;
> +}
> +
> +static u8 spi_nor_3to4_opcode(u8 opcode)
> +{
> +	/* MUST be sorted by 3byte opcode (cf spi_nor_convert_opcode). */
> +#define ENTRY_3TO4(_opcode)	{ _opcode, _opcode##_4B }
> +	static const struct spi_nor_address_entry spi_nor_3to4_table[] = {

You can make this static const struct const for extra constness :-)

> +		ENTRY_3TO4(SPINOR_OP_PP),		/* 0x02 */
> +		ENTRY_3TO4(SPINOR_OP_READ),		/* 0x03 */
> +		ENTRY_3TO4(SPINOR_OP_READ_FAST),	/* 0x0b */
> +		ENTRY_3TO4(SPINOR_OP_BE_4K),		/* 0x20 */
> +		ENTRY_3TO4(SPINOR_OP_PP_1_1_4),		/* 0x32 */
> +		ENTRY_3TO4(SPINOR_OP_PP_1_4_4),		/* 0x38 */
> +		ENTRY_3TO4(SPINOR_OP_READ_1_1_2),	/* 0x3b */
> +		ENTRY_3TO4(SPINOR_OP_BE_32K),		/* 0x52 */
> +		ENTRY_3TO4(SPINOR_OP_READ_1_1_4),	/* 0x6b */
> +		ENTRY_3TO4(SPINOR_OP_READ_1_2_2),	/* 0xbb */
> +		ENTRY_3TO4(SPINOR_OP_SE),		/* 0xd8 */
> +		ENTRY_3TO4(SPINOR_OP_READ_1_4_4),	/* 0xeb */

I'd probably break this into three smaller tables, read/program/erase
and then call something like:

spi_nor_3to4_opcode(nor->read_opcode, read_opcode_table,
                    ARRAY_SIZE(read_opcode_table));

This would further reduce the table size (heck, it'd probably fit into a
cacheline), so linear search would be more than enough.

> +	};
> +#undef ENTRY_3TO4
> +
> +	return spi_nor_convert_opcode(opcode, spi_nor_3to4_table,
> +				      ARRAY_SIZE(spi_nor_3to4_table));
> +}
> +
> +static void spi_nor_set_4byte_opcodes(struct spi_nor *nor,
> +				      const struct flash_info *info)
> +{
> +	/* Do some manufacturer fixups first */
> +	switch (JEDEC_MFR(info)) {
> +	case SNOR_MFR_SPANSION:
> +		/* No small sector erase for 4-byte command set */
> +		nor->erase_opcode = SPINOR_OP_SE;
> +		nor->mtd.erasesize = info->sector_size;
> +		break;
> +
> +	default:
> +		break;
> +	}
> +
> +	nor->read_opcode	= spi_nor_3to4_opcode(nor->read_opcode);
> +	nor->program_opcode	= spi_nor_3to4_opcode(nor->program_opcode);
> +	nor->erase_opcode	= spi_nor_3to4_opcode(nor->erase_opcode);
> +}
> +
>  /* Enable/disable 4-byte addressing mode. */
>  static inline int set_4byte(struct spi_nor *nor, const struct flash_info *info,
>  			    int enable)
> @@ -1486,27 +1575,10 @@ int spi_nor_scan(struct spi_nor *nor, const char *name, enum read_mode mode)
>  	else if (mtd->size > 0x1000000) {
>  		/* enable 4-byte addressing if the device exceeds 16MiB */
>  		nor->addr_width = 4;
> -		if (JEDEC_MFR(info) == SNOR_MFR_SPANSION) {
> -			/* Dedicated 4-byte command set */
> -			switch (nor->flash_read) {
> -			case SPI_NOR_QUAD:
> -				nor->read_opcode = SPINOR_OP_READ_1_1_4_4B;
> -				break;
> -			case SPI_NOR_DUAL:
> -				nor->read_opcode = SPINOR_OP_READ_1_1_2_4B;
> -				break;
> -			case SPI_NOR_FAST:
> -				nor->read_opcode = SPINOR_OP_READ_FAST_4B;
> -				break;
> -			case SPI_NOR_NORMAL:
> -				nor->read_opcode = SPINOR_OP_READ_4B;
> -				break;
> -			}
> -			nor->program_opcode = SPINOR_OP_PP_4B;
> -			/* No small sector erase for 4-byte command set */
> -			nor->erase_opcode = SPINOR_OP_SE_4B;
> -			mtd->erasesize = info->sector_size;
> -		} else
> +		if (JEDEC_MFR(info) == SNOR_MFR_SPANSION ||
> +		    info->flags & SPI_NOR_4B_OPCODES)
> +			spi_nor_set_4byte_opcodes(nor, info);
> +		else
>  			set_4byte(nor, info, 1);
>  	} else {
>  		nor->addr_width = 3;
> 


-- 
Best regards,
Marek Vasut