Re: [PATCH v1 2/2] commands: mmc_extcsd: fix enhanced-area / GPP size display arithmetic

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

On 6/17/26 12:34 PM, Johannes Schneider wrote:
> Per JEDEC eMMC 5.1 (JESD84-B51, February 2015), the displayed byte
> size for the enhanced user data area and for each general-purpose
> partition is the product of the SIZE_MULT bytes, the write-protect
> group size, the erase group size, and 512 KiB:
> 
>   §7.4.90 ENH_SIZE_MULT [142:140] (p. 219):
>     Enhanced User Data Area x Size =
>        (ENH_SIZE_MULT_2 * 2^16 + ENH_SIZE_MULT_1 * 2^8
>         + ENH_SIZE_MULT_0 * 2^0)
>        * HC_WP_GRP_SIZE * HC_ERASE_GRP_SIZE * 512 kBytes
> 
>   §7.4.89 GP_SIZE_MULT_GP0..GP3 [154:143] (p. 218):
>     General_Purpose_Partition_X Size =
>        (GP_SIZE_MULT_X_2 * 2^16 + GP_SIZE_MULT_X_1 * 2^8
>         + GP_SIZE_MULT_X_0 * 2^0)
>        * HC_WP_GRP_SIZE * HC_ERASE_GRP_SIZE * 512 kBytes
> 
> The displayed-size code in mmc_extcsd.c for ENH_SIZE_MULT and for
> all four GP_SIZE_MULT[0..3] cases instead *added* HC_WP_GRP_SIZE
> and HC_ERASE_GRP_SIZE before multiplying by the SIZE_MULT and
> SZ_512K factors, producing nonsensical values. The neighbouring
> MAX_ENH_SIZE_MULT case already uses the correct multiplication.
> Bring the five buggy cases in line.
> 
> Assisted-by: Claude:claude-opus-4-7
> Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>

Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

> ---
>  commands/mmc_extcsd.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/commands/mmc_extcsd.c b/commands/mmc_extcsd.c
> index e7b0fd82ee..b898bd8515 100644
> --- a/commands/mmc_extcsd.c
> +++ b/commands/mmc_extcsd.c
> @@ -1342,7 +1342,7 @@ static int print_field(u8 *reg, int index)
>  
>  	case EXT_CSD_ENH_SIZE_MULT:
>  		tmp = get_field_val(EXT_CSD_HC_WP_GRP_SIZE, 0, 0xFF);
> -		tmp = tmp + get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
> +		tmp = tmp * get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
>  		tmp64 *= tmp;
>  		tmp64 *= SZ_512K;
>  		printf("\tEnhanced User Data Area %i Size: %llu B\n",
> @@ -1351,7 +1351,7 @@ static int print_field(u8 *reg, int index)
>  
>  	case EXT_CSD_GP_SIZE_MULT3:
>  		tmp = get_field_val(EXT_CSD_HC_WP_GRP_SIZE, 0, 0xFF);
> -		tmp = tmp + get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
> +		tmp = tmp * get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
>  		tmp64 *= tmp;
>  		tmp64 *= SZ_512K;
>  		printf("\tGeneral_Purpose_Partition_3 Size: %llu B\n", tmp64);
> @@ -1359,7 +1359,7 @@ static int print_field(u8 *reg, int index)
>  
>  	case EXT_CSD_GP_SIZE_MULT2:
>  		tmp = get_field_val(EXT_CSD_HC_WP_GRP_SIZE, 0, 0xFF);
> -		tmp = tmp + get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
> +		tmp = tmp * get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
>  		tmp64 *= tmp;
>  		tmp64 *= SZ_512K;
>  		printf("\tGeneral_Purpose_Partition_2 Size: %llu B\n", tmp64);
> @@ -1367,7 +1367,7 @@ static int print_field(u8 *reg, int index)
>  
>  	case EXT_CSD_GP_SIZE_MULT1:
>  		tmp = get_field_val(EXT_CSD_HC_WP_GRP_SIZE, 0, 0xFF);
> -		tmp = tmp + get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
> +		tmp = tmp * get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
>  		tmp64 *= tmp;
>  		tmp64 *= SZ_512K;
>  		printf("\tGeneral_Purpose_Partition_1 Size: %llu B\n", tmp64);
> @@ -1375,7 +1375,7 @@ static int print_field(u8 *reg, int index)
>  
>  	case EXT_CSD_GP_SIZE_MULT0:
>  		tmp = get_field_val(EXT_CSD_HC_WP_GRP_SIZE, 0, 0xFF);
> -		tmp = tmp + get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
> +		tmp = tmp * get_field_val(EXT_CSD_HC_ERASE_GRP_SIZE, 0, 0xFF);
>  		tmp64 *= tmp;
>  		tmp64 *= SZ_512K;
>  		printf("\tGeneral_Purpose_Partition_0 Size: %llu B\n", tmp64);

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