Re: [PATCH v5 2/8] lib/bch: Allow easy bit swapping

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

On Tue, 19 May 2020 09:45:43 +0200
Miquel Raynal <miquel.raynal@bootlin.com> wrote:

> It seems that several hardware ECC engine use a swapped representation
> of bytes compared to software. This might having to do with how the
> ECC engine is wired to the NAND controller or the order the bits are
> passed to the hardware BCH logic.
> 
> This means that when the software BCH engine is working in conjunction
> with data generated with hardware, sometimes we might need to swap the
> bits inside bytes, eg:
> 
>     0x0A = b0000_1010 -> b0101_0000 = 0x50
> 
> Make it possible by adding a boolean to the BCH initialization routine.
> 
> Regarding the implementation itself, this is a rather simple approach
> that can probably be enhanced in the future by preparing the
> ->a_{mod,pow}_tab tables with the swapping in mind.  
> 
> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/mtd/devices/docg3.c     |  2 +-
>  drivers/mtd/nand/raw/nand_bch.c |  2 +-
>  include/linux/bch.h             |  5 +-
>  lib/bch.c                       | 90 ++++++++++++++++++++++++++++-----
>  4 files changed, 82 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/mtd/devices/docg3.c b/drivers/mtd/devices/docg3.c
> index 799df8d03357..a030792115bc 100644
> --- a/drivers/mtd/devices/docg3.c
> +++ b/drivers/mtd/devices/docg3.c
> @@ -1985,7 +1985,7 @@ static int __init docg3_probe(struct platform_device *pdev)
>  	cascade->base = base;
>  	mutex_init(&cascade->lock);
>  	cascade->bch = bch_init(DOC_ECC_BCH_M, DOC_ECC_BCH_T,
> -				DOC_ECC_BCH_PRIMPOLY);
> +				DOC_ECC_BCH_PRIMPOLY, false);
>  	if (!cascade->bch)
>  		return ret;
>  
> diff --git a/drivers/mtd/nand/raw/nand_bch.c b/drivers/mtd/nand/raw/nand_bch.c
> index d95fcc7358e9..d5af8c5fd02f 100644
> --- a/drivers/mtd/nand/raw/nand_bch.c
> +++ b/drivers/mtd/nand/raw/nand_bch.c
> @@ -130,7 +130,7 @@ struct nand_bch_control *nand_bch_init(struct mtd_info *mtd)
>  	if (!nbc)
>  		goto fail;
>  
> -	nbc->bch = bch_init(m, t, 0);
> +	nbc->bch = bch_init(m, t, 0, false);
>  	if (!nbc->bch)
>  		goto fail;
>  
> diff --git a/include/linux/bch.h b/include/linux/bch.h
> index 9c35e7cd5890..85fdce83d4e2 100644
> --- a/include/linux/bch.h
> +++ b/include/linux/bch.h
> @@ -33,6 +33,7 @@
>   * @cache:      log-based polynomial representation buffer
>   * @elp:        error locator polynomial
>   * @poly_2t:    temporary polynomials of degree 2t
> + * @swap_bits:  swap bits within data and syndrome bytes
>   */
>  struct bch_control {
>  	unsigned int    m;
> @@ -51,9 +52,11 @@ struct bch_control {
>  	int            *cache;
>  	struct gf_poly *elp;
>  	struct gf_poly *poly_2t[4];
> +	bool		swap_bits;
>  };
>  
> -struct bch_control *bch_init(int m, int t, unsigned int prim_poly);
> +struct bch_control *bch_init(int m, int t, unsigned int prim_poly,
> +			     bool swap_bits);
>  
>  void bch_free(struct bch_control *bch);
>  
> diff --git a/lib/bch.c b/lib/bch.c
> index 1091841ac716..7c031ee8b93b 100644
> --- a/lib/bch.c
> +++ b/lib/bch.c
> @@ -114,6 +114,49 @@ struct gf_poly_deg1 {
>  	unsigned int   c[2];
>  };
>  
> +static u8 swap_bits_table[] = {
> +	0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
> +	0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
> +	0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
> +	0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
> +	0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
> +	0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
> +	0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
> +	0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
> +	0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
> +	0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
> +	0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
> +	0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
> +	0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
> +	0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
> +	0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
> +	0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
> +	0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
> +	0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
> +	0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
> +	0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
> +	0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
> +	0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
> +	0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
> +	0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
> +	0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
> +	0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
> +	0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
> +	0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
> +	0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
> +	0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
> +	0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
> +	0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff,
> +};
> +
> +static u8 swap_bits(struct bch_control *bch, u8 in)
> +{
> +	if (!bch->swap_bits)
> +		return in;
> +
> +	return swap_bits_table[in];
> +}
> +
>  /*
>   * same as bch_encode(), but process input data one byte at a time
>   */
> @@ -126,7 +169,9 @@ static void bch_encode_unaligned(struct bch_control *bch,
>  	const int l = BCH_ECC_WORDS(bch)-1;
>  
>  	while (len--) {
> -		p = bch->mod8_tab + (l+1)*(((ecc[0] >> 24)^(*data++)) & 0xff);
> +		u8 tmp = swap_bits(bch, *data++);
> +
> +		p = bch->mod8_tab + (l+1)*(((ecc[0] >> 24)^(tmp)) & 0xff);
>  
>  		for (i = 0; i < l; i++)
>  			ecc[i] = ((ecc[i] << 8)|(ecc[i+1] >> 24))^(*p++);
> @@ -145,10 +190,16 @@ static void load_ecc8(struct bch_control *bch, uint32_t *dst,
>  	unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
>  
>  	for (i = 0; i < nwords; i++, src += 4)
> -		dst[i] = (src[0] << 24)|(src[1] << 16)|(src[2] << 8)|src[3];
> +		dst[i] = ((u32)swap_bits(bch, src[0]) << 24) |
> +			((u32)swap_bits(bch, src[1]) << 16) |
> +			((u32)swap_bits(bch, src[2]) << 8) |
> +			swap_bits(bch, src[3]);
>  
>  	memcpy(pad, src, BCH_ECC_BYTES(bch)-4*nwords);
> -	dst[nwords] = (pad[0] << 24)|(pad[1] << 16)|(pad[2] << 8)|pad[3];
> +	dst[nwords] = ((u32)swap_bits(bch, pad[0]) << 24) |
> +		((u32)swap_bits(bch, pad[1]) << 16) |
> +		((u32)swap_bits(bch, pad[2]) << 8) |
> +		swap_bits(bch, pad[3]);
>  }
>  
>  /*
> @@ -161,15 +212,15 @@ static void store_ecc8(struct bch_control *bch, uint8_t *dst,
>  	unsigned int i, nwords = BCH_ECC_WORDS(bch)-1;
>  
>  	for (i = 0; i < nwords; i++) {
> -		*dst++ = (src[i] >> 24);
> -		*dst++ = (src[i] >> 16) & 0xff;
> -		*dst++ = (src[i] >>  8) & 0xff;
> -		*dst++ = (src[i] >>  0) & 0xff;
> +		*dst++ = swap_bits(bch, src[i] >> 24);
> +		*dst++ = swap_bits(bch, src[i] >> 16);
> +		*dst++ = swap_bits(bch, src[i] >> 8);
> +		*dst++ = swap_bits(bch, src[i]);
>  	}
> -	pad[0] = (src[nwords] >> 24);
> -	pad[1] = (src[nwords] >> 16) & 0xff;
> -	pad[2] = (src[nwords] >>  8) & 0xff;
> -	pad[3] = (src[nwords] >>  0) & 0xff;
> +	pad[0] = swap_bits(bch, src[nwords] >> 24);
> +	pad[1] = swap_bits(bch, src[nwords] >> 16);
> +	pad[2] = swap_bits(bch, src[nwords] >> 8);
> +	pad[3] = swap_bits(bch, src[nwords]);
>  	memcpy(dst, pad, BCH_ECC_BYTES(bch)-4*nwords);
>  }
>  
> @@ -240,7 +291,13 @@ void bch_encode(struct bch_control *bch, const uint8_t *data,
>  	 */
>  	while (mlen--) {
>  		/* input data is read in big-endian format */
> -		w = r[0]^cpu_to_be32(*pdata++);
> +		w = cpu_to_be32(*pdata++);
> +		if (bch->swap_bits)
> +			w = (u32)swap_bits(bch, w) |
> +			    ((u32)swap_bits(bch, w >> 8) << 8) |
> +			    ((u32)swap_bits(bch, w >> 16) << 16) |
> +			    ((u32)swap_bits(bch, w >> 24) << 24);
> +		w ^= r[0];
>  		p0 = tab0 + (l+1)*((w >>  0) & 0xff);
>  		p1 = tab1 + (l+1)*((w >>  8) & 0xff);
>  		p2 = tab2 + (l+1)*((w >> 16) & 0xff);
> @@ -1048,7 +1105,9 @@ int bch_decode(struct bch_control *bch, const uint8_t *data, unsigned int len,
>  				break;
>  			}
>  			errloc[i] = nbits-1-errloc[i];
> -			errloc[i] = (errloc[i] & ~7)|(7-(errloc[i] & 7));
> +			if (!bch->swap_bits)
> +				errloc[i] = (errloc[i] & ~7) |
> +					    (7-(errloc[i] & 7));
>  		}
>  	}
>  	return (err >= 0) ? err : -EBADMSG;
> @@ -1240,6 +1299,7 @@ static uint32_t *compute_generator_polynomial(struct bch_control *bch)
>   * @m:          Galois field order, should be in the range 5-15
>   * @t:          maximum error correction capability, in bits
>   * @prim_poly:  user-provided primitive polynomial (or 0 to use default)
> + * @swap_bits:  swap bits within data and syndrome bytes
>   *
>   * Returns:
>   *  a newly allocated BCH control structure if successful, NULL otherwise
> @@ -1256,7 +1316,8 @@ static uint32_t *compute_generator_polynomial(struct bch_control *bch)
>   * BCH control structure, ecc length in bytes is given by member @ecc_bytes of
>   * the structure.
>   */
> -struct bch_control *bch_init(int m, int t, unsigned int prim_poly)
> +struct bch_control *bch_init(int m, int t, unsigned int prim_poly,
> +			     bool swap_bits)
>  {
>  	int err = 0;
>  	unsigned int i, words;
> @@ -1321,6 +1382,7 @@ struct bch_control *bch_init(int m, int t, unsigned int prim_poly)
>  	bch->syn       = bch_alloc(2*t*sizeof(*bch->syn), &err);
>  	bch->cache     = bch_alloc(2*t*sizeof(*bch->cache), &err);
>  	bch->elp       = bch_alloc((t+1)*sizeof(struct gf_poly_deg1), &err);
> +	bch->swap_bits = swap_bits;
>  
>  	for (i = 0; i < ARRAY_SIZE(bch->poly_2t); i++)
>  		bch->poly_2t[i] = bch_alloc(GF_POLY_SZ(2*t), &err);


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