Re: [PATCH v2] crypto: crc32: make crc32 available in PBL

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 29.08.23 16:38, Johannes Zink wrote:
> crc32 may be required in PBL for checking data integrity. Add it to PBL
> when CONFIG_CRC32 is enabled.
> 
> To save some memory use a slower-but-smaller variant of the crc32 algorithm
> in the PBL.
> 
> Signed-off-by: Johannes Zink <j.zink@pengutronix.de>
> ---
> To: Barebox Mailing List <barebox@lists.infradead.org>
> Cc: Johannes Zink <j.zink@pengutronix.de>
> Cc: patchwork-jzi@pengutronix.de
> ---
> 
> Changes:
> 
> v1->v2: Worked in Ahmad's review (thank you for reviewing my patch):
>   - instead of using CRC32_EARLY, always add crc32.o to obj and pbl if
>     CONFIG_CRC is set and rely on LTO to remove unused symbols instead

fyi, LTO goes beyond linker garbage collection and actively rewrites
code, while --gc-sections, just checks which data/code sections are unused
and drops the dead code/data. We don't (yet) do LTO in barebox.

Patch looks good otherwise:
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

>   - use a CRC32 implementation without a prepopulated Lookup Table,
>     which trades in speed for code size in the PBL, analogously to what
>     Sascha implemented in [1]
>   - add hints on some of the #endifs for better readability of nested
>     ifdef blocks
>   - reword commit message to reflect on the changes made
> 
>     [1] 2d13b856604b ("crc: Add PBL variant for crc_itu_t()")
> ---
>  crypto/Makefile |  2 +-
>  crypto/crc32.c  | 34 ++++++++++++++++++++++++++++------
>  2 files changed, 29 insertions(+), 7 deletions(-)
> 
> diff --git a/crypto/Makefile b/crypto/Makefile
> index 22035d4f69ee..4a1c7e9615b8 100644
> --- a/crypto/Makefile
> +++ b/crypto/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  
> -obj-$(CONFIG_CRC32)	+= crc32.o
> +obj-pbl-$(CONFIG_CRC32)	+= crc32.o
>  obj-pbl-$(CONFIG_CRC_ITU_T)	+= crc-itu-t.o
>  obj-$(CONFIG_CRC7)	+= crc7.o
>  obj-$(CONFIG_DIGEST)	+= digest.o
> diff --git a/crypto/crc32.c b/crypto/crc32.c
> index 95cb2212db2b..2cf13144c1d2 100644
> --- a/crypto/crc32.c
> +++ b/crypto/crc32.c
> @@ -22,7 +22,7 @@
>  #define STATIC static inline
>  #endif
>  
> -#ifdef CONFIG_DYNAMIC_CRC_TABLE
> +#if defined(CONFIG_DYNAMIC_CRC_TABLE) && !defined(__PBL__)
>  
>  static uint32_t *crc_table;
>  
> @@ -73,7 +73,7 @@ static void make_crc_table(void)
>      crc_table[n] = c;
>    }
>  }
> -#else
> +#elif !defined(__PBL__)
>  /* ========================================================================
>   * Table of CRC-32's of all single-byte values (made by make_crc_table)
>   */
> @@ -131,9 +131,30 @@ static const uint32_t crc_table[256] = {
>    0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
>    0x2d02ef8dL
>  };
> -#endif
> +#endif /* defined(CONFIG_DYNAMIC_CRC_TABLE) && !defined(__PBL__) */
> +
> +
> +
> +#ifdef __PBL__
> +#define CRC32_POLY 0xEDB88320L
> +STATIC uint32_t crc32(uint32_t crc, const void *_buf, unsigned int len)
> +{
> +	int i, j;
> +	const unsigned char *buf = _buf;
>  
> +	crc = crc ^ 0xffffffffL;
>  
> +	for (i=0; i< len; i++) {
> +		crc ^= buf[i];
> +		for (j = 0; j < 8; j++) {
> +			crc = (crc >> 1) ^ ((crc & 1) ? CRC32_POLY : 0);
> +		}
> +	}
> +
> +	crc = crc ^ 0xffffffffL;
> +	return crc;
> +}
> +#else
>  /* ========================================================================= */
>  #define DO1(buf) crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
>  #define DO2(buf)  DO1(buf); DO1(buf);
> @@ -148,7 +169,7 @@ STATIC uint32_t crc32(uint32_t crc, const void *_buf, unsigned int len)
>  #ifdef CONFIG_DYNAMIC_CRC_TABLE
>  	if (!crc_table)
>  		make_crc_table();
> -#endif
> +#endif /* CONFIG_DYNAMIC_CRC_TABLE */
>      crc = crc ^ 0xffffffffL;
>      while (len >= 8)
>      {
> @@ -162,7 +183,7 @@ STATIC uint32_t crc32(uint32_t crc, const void *_buf, unsigned int len)
>  }
>  #ifdef __BAREBOX__
>  EXPORT_SYMBOL(crc32);
> -#endif
> +#endif /* __BAREBOX__ */
>  
>  /* No ones complement version. JFFS2 (and other things ?)
>   * don't use ones compliment in their CRC calculations.
> @@ -174,7 +195,7 @@ STATIC uint32_t crc32_no_comp(uint32_t crc, const void *_buf, unsigned int len)
>  #ifdef CONFIG_DYNAMIC_CRC_TABLE
>  	if (!crc_table)
>  		make_crc_table();
> -#endif
> +#endif /* CONFIG_DYNAMIC_CRC_TABLE */
>      while (len >= 8)
>      {
>        DO8(buf);
> @@ -186,6 +207,7 @@ STATIC uint32_t crc32_no_comp(uint32_t crc, const void *_buf, unsigned int len)
>  
>      return crc;
>  }
> +#endif /* __PBL__ */
>  
>  STATIC uint32_t crc32_be(uint32_t crc, const void *_buf, unsigned int len)
>  {
> 
> ---
> base-commit: bef38b18eeb5d2f1fac334fb8b831e47261e099c
> change-id: 20230829-crc32_in_pbl-4d824629d4e2
> 
> Best regards,

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |