Re: [PATCH v3 4/8] mtd: rawnand: Add nand_extract_bits()

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu,  7 May 2020 13:00:30 +0200
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> There are cases where ECC bytes are not byte-aligned. Indeed, BCH
> implies using a number of ECC bits, which are not always a multiple of
> 8. We then need a helper like nand_extract_bits() to extract these
> syndromes from a buffer.

Do you plan to send a patch to make the GPMI driver use this helper?

> 
> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> ---
>  drivers/mtd/nand/raw/nand_base.c | 31 +++++++++++++++++++++++++++++++
>  include/linux/mtd/rawnand.h      |  4 ++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index 25d298938aa9..b236e1bdddaf 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -224,6 +224,37 @@ static int check_offs_len(struct nand_chip *chip, loff_t ofs, uint64_t len)
>  	return ret;
>  }
>  
> +/* Copy unaligned bits from one buffer to another one (no overlap) */
> +void nand_extract_bits(u8 *dst, const u8 *src, unsigned int src_off,
> +		       unsigned int nbits)
> +{
> +	unsigned int dst_off = 0, tmp, n;
> +
> +	src += src_off / 8;
> +	src_off %= 8;
> +
> +	while (nbits) {
> +		n = min3(8 - dst_off, 8 - src_off, nbits);
> +
> +		tmp = (*src >> src_off) & GENMASK(n - 1, 0);
> +		*dst |= tmp << dst_off;
> +
> +		dst_off += n;
> +		if (dst_off >= 8) {
> +			dst++;
> +			dst_off -= 8;
> +		}
> +
> +		src_off += n;
> +		if (src_off >= 8) {
> +			src++;
> +			src_off -= 8;
> +		}
> +
> +		nbits -= n;
> +	}
> +}
> +
>  /**
>   * nand_select_target() - Select a NAND target (A.K.A. die)
>   * @chip: NAND chip object
> diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
> index 406e9ff0f45c..734564232545 100644
> --- a/include/linux/mtd/rawnand.h
> +++ b/include/linux/mtd/rawnand.h
> @@ -1404,6 +1404,10 @@ int nand_gpio_waitrdy(struct nand_chip *chip, struct gpio_desc *gpiod,
>  void nand_select_target(struct nand_chip *chip, unsigned int cs);
>  void nand_deselect_target(struct nand_chip *chip);
>  
> +/* Bitops */
> +void nand_extract_bits(u8 *dst, const u8 *src, unsigned int src_off,
> +		       unsigned int nbits);
> +
>  /**
>   * nand_get_data_buf() - Get the internal page buffer
>   * @chip: NAND chip object