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Date:   Wed, 2 Mar 2022 17:04:49 +0530
From:   Pratyush Yadav <p.yadav@ti.com>
To:     Tudor Ambarus <tudor.ambarus@microchip.com>
CC:     <michael@walle.cc>, <broonie@kernel.org>,
        <miquel.raynal@bootlin.com>, <richard@nod.at>, <vigneshr@ti.com>,
        <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <linux-spi@vger.kernel.org>, <nicolas.ferre@microchip.com>,
        <zhengxunli@mxic.com.tw>, <jaimeliao@mxic.com.tw>
Subject: Re: [PATCH 2/4] mtd: spi-nor: core: Allow specifying the byte order
 in DTR mode
Message-ID: <20220302113449.tc2iipvwtaxavfec@ti.com>
References: <20220218145900.1440045-1-tudor.ambarus@microchip.com>
 <20220218145900.1440045-3-tudor.ambarus@microchip.com>
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In-Reply-To: <20220218145900.1440045-3-tudor.ambarus@microchip.com>
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Hi Tudor,

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?

>  
>  #define SNOR_PROTO_STR(_inst_nbits, _addr_nbits, _data_nbits)	\
>  	(SNOR_PROTO_INST(_inst_nbits) |				\
> @@ -201,6 +206,18 @@ static inline bool spi_nor_protocol_is_dtr(enum spi_nor_protocol proto)
>  	return !!(proto & SNOR_PROTO_IS_DTR);
>  }
>  
> +static inline bool spi_nor_protocol_is_octal_dtr(enum spi_nor_protocol proto)
> +{
> +	return ((proto & SNOR_PROTO_8_8_8_DTR) == SNOR_PROTO_8_8_8_DTR);
> +}
> +
> +static inline bool spi_nor_protocol_is_dtr_bswap16(enum spi_nor_protocol proto)
> +{
> +	u32 mask = SNOR_PROTO_IS_DTR | SNOR_PROTO_IS_DTR_BSWAP16;
> +
> +	return ((proto & mask) == mask);
> +}
> +
>  static inline u8 spi_nor_get_protocol_inst_nbits(enum spi_nor_protocol proto)
>  {
>  	return ((unsigned long)(proto & SNOR_PROTO_INST_MASK)) >>
> -- 
> 2.25.1
> 

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.