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

[Cyrille Pitchen]

Le 07/12/2016 Ã 17:20, Marek Vasut a Ãcrit :
> 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@xxxxxxxxx>
>> Tested-by: Vignesh R <vigneshr@xxxxxx>
>> ---
>>  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.

Well ok, I agree with you, it's too much overkill for what it does.
For readiness purpose, what about a simple and straight forward switch()
statement? Let's forget about cache-line and other memory/time optimizations :)

> 
>> +	/* 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;
>>
> 
>