Re: [PATCH] ddr_spd: use unsigned type for crc bytes in DDR3/4 SPD check

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, Jan 13, 2023 at 05:06:48PM +0300, Denis Orlov wrote:
> Using signed char type for computed CRC bytes leads to them being sign
> extended on comparison with unsigned char values from SPD EEPROM struct.
> This happens as when being compared those values undergo integer
> promotion that converts them into ints, sign extending signed types.
> Having most significant byte set for any of computed CRC bytes thus
> results in the mismatch being erroneously detected.
> 
> While at it, also remove redundant type casts.
> 
> Signed-off-by: Denis Orlov <denorl2009@gmail.com>
> ---
>  common/ddr_spd.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)

Applied, thanks

Sascha

> 
> diff --git a/common/ddr_spd.c b/common/ddr_spd.c
> index 52773178e7..dd3b8511e6 100644
> --- a/common/ddr_spd.c
> +++ b/common/ddr_spd.c
> @@ -65,8 +65,8 @@ int ddr3_spd_check(const struct ddr3_spd_eeprom *spd)
>  	char *p = (char *)spd;
>  	int csum16;
>  	int len;
> -	char crc_lsb;	/* byte 126 */
> -	char crc_msb;	/* byte 127 */
> +	unsigned char crc_lsb;	/* byte 126 */
> +	unsigned char crc_msb;	/* byte 127 */
>  
>  	/*
>  	 * SPD byte0[7] - CRC coverage
> @@ -77,8 +77,8 @@ int ddr3_spd_check(const struct ddr3_spd_eeprom *spd)
>  	len = !(spd->info_size_crc & 0x80) ? 126 : 117;
>  	csum16 = crc_itu_t(0, p, len);
>  
> -	crc_lsb = (char) (csum16 & 0xff);
> -	crc_msb = (char) (csum16 >> 8);
> +	crc_lsb = csum16 & 0xff;
> +	crc_msb = csum16 >> 8;
>  
>  	if (spd->crc[0] == crc_lsb && spd->crc[1] == crc_msb) {
>  		return 0;
> @@ -96,14 +96,14 @@ int ddr4_spd_check(const struct ddr4_spd_eeprom *spd)
>  	char *p = (char *)spd;
>  	int csum16;
>  	int len;
> -	char crc_lsb;	/* byte 126 */
> -	char crc_msb;	/* byte 127 */
> +	unsigned char crc_lsb;	/* byte 126 */
> +	unsigned char crc_msb;	/* byte 127 */
>  
>  	len = 126;
>  	csum16 = crc_itu_t(0, p, len);
>  
> -	crc_lsb = (char) (csum16 & 0xff);
> -	crc_msb = (char) (csum16 >> 8);
> +	crc_lsb = csum16 & 0xff;
> +	crc_msb = csum16 >> 8;
>  
>  	if (spd->crc[0] != crc_lsb || spd->crc[1] != crc_msb) {
>  		printf("SPD checksum unexpected.\n"
> @@ -117,8 +117,8 @@ int ddr4_spd_check(const struct ddr4_spd_eeprom *spd)
>  	len = 126;
>  	csum16 = crc_itu_t(0, p, len);
>  
> -	crc_lsb = (char) (csum16 & 0xff);
> -	crc_msb = (char) (csum16 >> 8);
> +	crc_lsb = csum16 & 0xff;
> +	crc_msb = csum16 >> 8;
>  
>  	if (spd->mod_section.uc[126] != crc_lsb ||
>  	    spd->mod_section.uc[127] != crc_msb) {
> -- 
> 2.30.2
> 
> 

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