Re: [PATCH 2/4] mtd: spi-nor: core: Allow specifying the byte order in DTR mode

[<Tudor.Ambarus@microchip.com>]

On 3/2/22 13:34, Pratyush Yadav wrote:
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> 
> Hi Tudor,

Hi, Pratyush,

> 
> On 18/02/22 04:58PM, Tudor Ambarus wrote:
>> Macronix swaps bytes on a 16-bit boundary when configured in Octal DTR.
>> The byte order of 16-bit words is swapped when read or write written in
>> 8D-8D-8D mode compared to STR modes. Swapping the bytes is a bad design
>> decision because this may affect the boot sequence if the entire boot
>> sequence is not handled in either 8D-8D-8D mode or 1-1-1 mode. Allow
>> operations to specify the byte order in DTR mode, so that controllers can
>> swap the bytes back at run-time to fix the endianness, if they are capable.
>>
>> The byte order in 8D-8D-8D mode can be retrieved at run-time by checking
>> BFPT[DWORD(18)] BIT(31). When set to one, the "Byte order of 16-bit words
>> is swapped when read in 8D-8D-8D mode compared to 1-1-1 mode.". It doesn't
>> specify if this applies to both register and data operations. Macronix is
>> the single user of this byte swap and it doesn't have clear rules, as it
>> contains register operations that require data swap (RDPASS, WRPASS,
>> PASSULK, RDSFDP) and register operations that don't require data swap
>> (WRFBR). All these are not common and can be handled in 1-1-1 mode, so we
>> can ignore them for now. All the other register operations are done on one
>> byte length. The read register operations are actually in 8D-8D-8S mode,
>> as they send the data value twice, on each half of the clock cycle. In case
>> of a register write of one byte, the memory supports receiving the register
>> value only on the first byte, thus it discards the value of the byte on the
>> second half of the clock cycle. Swapping the bytes for one byte register
>> writes is not required, and for one byte register reads it doesn't matter.
>> Thus swap the bytes only for read or page program operations.
>>
>> Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
>> ---
>>  drivers/mtd/spi-nor/core.c  | 31 +++++++++++++++++++++++++------
>>  drivers/mtd/spi-nor/core.h  |  1 +
>>  include/linux/mtd/spi-nor.h | 17 +++++++++++++++++
>>  3 files changed, 43 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
>> index 04ea180118e3..453d8c54d062 100644
>> --- a/drivers/mtd/spi-nor/core.c
>> +++ b/drivers/mtd/spi-nor/core.c
>> @@ -106,6 +106,9 @@ void spi_nor_spimem_setup_op(const struct spi_nor *nor,
>>               op->dummy.dtr = true;
>>               op->data.dtr = true;
>>
>> +             if (spi_nor_protocol_is_dtr_bswap16(proto))
>> +                     op->data.dtr_bswap16 = true;
>> +
>>               /* 2 bytes per clock cycle in DTR mode. */
>>               op->dummy.nbytes *= 2;
>>
>> @@ -388,7 +391,7 @@ int spi_nor_read_sr(struct spi_nor *nor, u8 *sr)
>>                                  SPI_MEM_OP_NO_DUMMY,
>>                                  SPI_MEM_OP_DATA_IN(1, sr, 0));
>>
>> -             if (nor->reg_proto == SNOR_PROTO_8_8_8_DTR) {
>> +             if (spi_nor_protocol_is_octal_dtr(nor->reg_proto)) {
>>                       op.addr.nbytes = nor->params->rdsr_addr_nbytes;
>>                       op.dummy.nbytes = nor->params->rdsr_dummy;
>>                       /*
>> @@ -432,7 +435,7 @@ static int spi_nor_read_fsr(struct spi_nor *nor, u8 *fsr)
>>                                  SPI_MEM_OP_NO_DUMMY,
>>                                  SPI_MEM_OP_DATA_IN(1, fsr, 0));
>>
>> -             if (nor->reg_proto == SNOR_PROTO_8_8_8_DTR) {
>> +             if (spi_nor_protocol_is_octal_dtr(nor->reg_proto)) {
>>                       op.addr.nbytes = nor->params->rdsr_addr_nbytes;
>>                       op.dummy.nbytes = nor->params->rdsr_dummy;
>>                       /*
>> @@ -2488,7 +2491,7 @@ static int spi_nor_set_addr_width(struct spi_nor *nor)
>>  {
>>       if (nor->addr_width) {
>>               /* already configured from SFDP */
>> -     } else if (nor->read_proto == SNOR_PROTO_8_8_8_DTR) {
>> +     } else if (spi_nor_protocol_is_octal_dtr(nor->read_proto)) {
>>               /*
>>                * In 8D-8D-8D mode, one byte takes half a cycle to transfer. So
>>                * in this protocol an odd address width cannot be used because
>> @@ -2701,6 +2704,19 @@ static void spi_nor_init_fixup_flags(struct spi_nor *nor)
>>               nor->flags |= SNOR_F_IO_MODE_EN_VOLATILE;
>>  }
>>
>> +static void spi_nor_set_dtr_bswap16_ops(struct spi_nor *nor)
>> +{
>> +     struct spi_nor_flash_parameter *params = nor->params;
>> +     u32 mask = SNOR_HWCAPS_READ_8_8_8_DTR | SNOR_HWCAPS_PP_8_8_8_DTR;
>> +
>> +     if ((params->hwcaps.mask & mask) == mask) {
>> +             params->reads[SNOR_CMD_READ_8_8_8_DTR].proto |=
>> +                     SNOR_PROTO_IS_DTR_BSWAP16;
>> +             params->page_programs[SNOR_CMD_PP_8_8_8_DTR].proto |=
>> +                     SNOR_PROTO_IS_DTR_BSWAP16;
>> +     }
>> +}
>> +
>>  /**
>>   * spi_nor_late_init_params() - Late initialization of default flash parameters.
>>   * @nor:     pointer to a 'struct spi_nor'
>> @@ -2721,6 +2737,9 @@ static void spi_nor_late_init_params(struct spi_nor *nor)
>>       spi_nor_init_flags(nor);
>>       spi_nor_init_fixup_flags(nor);
>>
>> +     if (nor->flags & SNOR_F_DTR_BSWAP16)
>> +             spi_nor_set_dtr_bswap16_ops(nor);
>> +
>>       /*
>>        * NOR protection support. When locking_ops are not provided, we pick
>>        * the default ones.
>> @@ -2899,8 +2918,8 @@ static int spi_nor_octal_dtr_enable(struct spi_nor *nor, bool enable)
>>       if (!nor->params->octal_dtr_enable)
>>               return 0;
>>
>> -     if (!(nor->read_proto == SNOR_PROTO_8_8_8_DTR &&
>> -           nor->write_proto == SNOR_PROTO_8_8_8_DTR))
>> +     if (!(spi_nor_protocol_is_octal_dtr(nor->read_proto) &&
>> +           spi_nor_protocol_is_octal_dtr(nor->write_proto)))
>>               return 0;
>>
>>       if (!(nor->flags & SNOR_F_IO_MODE_EN_VOLATILE))
>> @@ -2968,7 +2987,7 @@ static int spi_nor_init(struct spi_nor *nor)
>>               spi_nor_try_unlock_all(nor);
>>
>>       if (nor->addr_width == 4 &&
>> -         nor->read_proto != SNOR_PROTO_8_8_8_DTR &&
>> +         !spi_nor_protocol_is_octal_dtr(nor->read_proto) &&
>>           !(nor->flags & SNOR_F_4B_OPCODES)) {
>>               /*
>>                * If the RESET# pin isn't hooked up properly, or the system
>> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
>> index 2afb610853a9..7c077d41c335 100644
>> --- a/drivers/mtd/spi-nor/core.h
>> +++ b/drivers/mtd/spi-nor/core.h
>> @@ -29,6 +29,7 @@ enum spi_nor_option_flags {
>>       SNOR_F_IO_MODE_EN_VOLATILE = BIT(14),
>>       SNOR_F_SOFT_RESET       = BIT(15),
>>       SNOR_F_SWP_IS_VOLATILE  = BIT(16),
>> +     SNOR_F_DTR_BSWAP16      = BIT(17),
>>  };
>>
>>  struct spi_nor_read_command {
>> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
>> index fc90fce26e33..6e9660475c5b 100644
>> --- a/include/linux/mtd/spi-nor.h
>> +++ b/include/linux/mtd/spi-nor.h
>> @@ -168,6 +168,11 @@
>>        SNOR_PROTO_DATA_MASK)
>>
>>  #define SNOR_PROTO_IS_DTR    BIT(24) /* Double Transfer Rate */
>> +/*
>> + * Byte order of 16-bit words is swapped when read or written in DTR mode
>> + * compared to STR mode.
>> + */
>> +#define SNOR_PROTO_IS_DTR_BSWAP16    BIT(25)
> 
> I am not so sure if the protocol is the best place to encode this. The
> protocol stays the same regardless of the data organisation. Maybe all
> we need to do is add something like
> 
> static inline bool
> spi_nor_needs_bswap16(struct spi_nor *nor, enum spi_nor_protocol proto)
> {
>         return (proto == SNOR_PROTO_8_8_8_DTR) && (nor->flags & SNOR_F_DTR_BSWAP16);
> }
> 
> And then call it from spi_nor_spimem_setup_op(). Thoughts?
> 

I find it better. There's no such thing as a 8D-8D-8D-bswap16 in
the standard terminology, so I'll drop the protocol handling.

Thanks!
ta
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