Re: [PATCH 6/6] mtd: spi-nor: core; avoid odd length/address writes in 8D-8D-8D mode

[Michael Walle <michael@walle.cc>]

Am 2021-05-06 21:18, schrieb Pratyush Yadav:
> On Octal DTR capable flashes like Micron Xcella the writes cannot start
> or end at an odd address in Octal DTR mode. Extra 0xff bytes need to be
> appended or prepended to make sure the start address and end address 
> are
> even. 0xff is used because on NOR flashes a program operation can only
> flip bits from 1 to 0, not the other way round. 0 to 1 flip needs to
> happen via erases.
> 
> Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
> 
> ---
> 
>  drivers/mtd/spi-nor/core.c | 72 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 71 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 3d66cc34af4d..265d8b25fc7f 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -2022,6 +2022,71 @@ static int spi_nor_read(struct mtd_info *mtd,
> loff_t from, size_t len,
>  	return ret;
>  }
> 
> +/*
> + * On Octal DTR capable flashes like Micron Xcella the writes cannot 
> start or
> + * end at an odd address in Octal DTR mode. Extra 0xff bytes need to
> be appended
> + * or prepended to make sure the start address and end address are
> even. 0xff is
> + * used because on NOR flashes a program operation can only flip bits 
> from 1 to
> + * 0, not the other way round. 0 to 1 flip needs to happen via erases.
> + */
> +static int spi_nor_octal_dtr_write(struct spi_nor *nor, loff_t to, 
> size_t len,
> +				   const u8 *buf)
> +{
> +	u8 *tmp_buf;
> +	size_t bytes_written;
> +	loff_t start, end;
> +	int ret;
> +
> +	if (IS_ALIGNED(to, 2) && IS_ALIGNED(len, 2))
> +		return spi_nor_write_data(nor, to, len, buf);
> +
> +	tmp_buf = kmalloc(nor->page_size, GFP_KERNEL);
> +	if (!tmp_buf)
> +		return -ENOMEM;
> +
> +	memset(tmp_buf, 0xff, nor->page_size);

This could be replaced by just setting the first and the
last byte to 0xff. But this might be easier to read. I am
fine with both.

> +
> +	start = round_down(to, 2);
> +	end = round_up(to + len, 2);
> +
> +	memcpy(tmp_buf + (to - start), buf, len);
> +
> +	ret = spi_nor_write_data(nor, start, end - start, tmp_buf);
> +	if (ret == 0) {
> +		ret = -EIO;
> +		goto out;
> +	}
else if ? I've missed this in the other patch.

> +	if (ret < 0)
> +		goto out;
> +
> +	/*
> +	 * More bytes are written than actually requested, but that number 
> can't
> +	 * be reported to the calling function or it will confuse its
> +	 * calculations. Calculate how many of the _requested_ bytes were
> +	 * written.
> +	 */
> +	bytes_written = ret;
> +
> +	if (to != start)
> +		ret -= to - start;
> +
> +	/*
> +	 * Only account for extra bytes at the end if they were actually
> +	 * written. For example, if for some reason the controller could only
> +	 * complete a partial write then the adjustment for the extra bytes 
> at
> +	 * the end is not needed.
> +	 */
> +	if (start + bytes_written == end)
> +		ret -= end - (to + len);
> +
> +	if (ret < 0)
> +		ret = -EIO;

can this happen?

> +
> +out:
> +	kfree(tmp_buf);
> +	return ret;
> +}
> +
>  /*
>   * Write an address range to the nor chip.  Data must be written in
>   * FLASH_PAGESIZE chunks.  The address range may be any size provided
> @@ -2066,7 +2131,12 @@ static int spi_nor_write(struct mtd_info *mtd,
> loff_t to, size_t len,
>  		if (ret)
>  			goto write_err;
> 
> -		ret = spi_nor_write_data(nor, addr, page_remain, buf + i);
> +		if (nor->write_proto == SNOR_PROTO_8_8_8_DTR)
> +			ret = spi_nor_octal_dtr_write(nor, addr, page_remain,
> +						      buf + i);
> +		else
> +			ret = spi_nor_write_data(nor, addr, page_remain,
> +						 buf + i);
>  		if (ret < 0)
>  			goto write_err;
>  		written = ret;

-michael