[PATCH 3/3] env: mmc: fix offsets relative to the end of the partition

[Quentin Schulz]

Hi Michael,

On 3/12/25 8:40 AM, Michael Walle wrote:
> According to the help text, you can set negative offsets to indicated
> that the offset is relative to the end of the parition. But kconfig
> doesn't let you specify negative hex values. I think this fell through
> the cracks when converting the symbol from a '#define' to a kconfig
> option.
> 
> Introduce a new boolean kconfig option to switch on the "relative to the
> end" behavior.
> 
> Signed-off-by: Michael Walle <mwalle at kernel.org>
> ---
>   env/Kconfig | 42 +++++++++++++++++++++++++-----------------
>   env/mmc.c   |  8 ++++++++
>   2 files changed, 33 insertions(+), 17 deletions(-)
> 
> diff --git a/env/Kconfig b/env/Kconfig
> index 4438f0b392c..49888bf700c 100644
> --- a/env/Kconfig
> +++ b/env/Kconfig
> @@ -231,14 +231,6 @@ config ENV_IS_IN_MMC
>   	  These two #defines specify the offset and size of the environment
>   	  area within the specified MMC device.
>   
> -	  If offset is positive (the usual case), it is treated as relative to
> -	  the start of the MMC partition. If offset is negative, it is treated
> -	  as relative to the end of the MMC partition. This can be useful if
> -	  your board may be fitted with different MMC devices, which have
> -	  different sizes for the MMC partitions, and you always want the
> -	  environment placed at the very end of the partition, to leave the
> -	  maximum possible space before it, to store other data.
> -
>   	  These two values are in units of bytes, but must be aligned to an
>   	  MMC sector boundary.
>   
> @@ -249,9 +241,6 @@ config ENV_IS_IN_MMC
>   	  valid backup copy in case the other copy is corrupted, e.g. due
>   	  to a power failure during a "saveenv" operation.
>   
> -	  This value may also be positive or negative; this is handled in the
> -	  same way as CONFIG_ENV_OFFSET.
> -
>   	  In case CONFIG_SYS_MMC_ENV_PART is 1 (i.e. environment in eMMC boot
>   	  partition) then setting CONFIG_ENV_OFFSET_REDUND to the same value
>   	  as CONFIG_ENV_OFFSET makes use of the second eMMC boot partition for
> @@ -592,9 +581,18 @@ config ENV_OFFSET
>   	  Offset from the start of the device (or partition).
>   
>   	  This offset may be interpreted differently depending on the chosen
> -	  ENV_IS_IN_* options. For example, for ENV_IS_IN_MMC=y, this offset may
> -	  be negative to indicate an offset backwards from the end of the
> -	  partition. See the relevant help messages for more details.
> +	  ENV_IS_IN_* options. See the relevant help messages for more details.
> +
> +config ENV_OFFSET_RELATIVE_END
> +	bool "Offset is relative to the end of the partition"
> +	depends on ENV_IS_IN_MMC
> +	help
> +	  Treat the environment offset as relative to the end of the MMC
> +	  partition. This can be useful if your board may be fitted with

I guess by MMC partition you meant hardware MMC partitions, as opposed 
to GPT/MBR partitions?

It's not clear from JEDEC standard if there's a word that would apply to 
the boot partitions, User Area (I think it can be split also?), RPMB, 
etc.? But if there's one, maybe use that term?

> +	  different MMC devices, which have different sizes for the MMC
> +	  partitions, and you always want the environment placed at the very end
> +	  of the partition, to leave the maximum possible space before it, to
> +	  store other data.
>   
>   config ENV_OFFSET_REDUND
>   	hex "Redundant environment offset"
> @@ -607,9 +605,19 @@ config ENV_OFFSET_REDUND
>   	  environment location.
>   
>   	  This offset may be interpreted differently depending on the chosen
> -	  ENV_IS_IN_* options. For example, for ENV_IS_IN_MMC=y, this offset may
> -	  be negative to indicate an offset backwards from the end of the
> -	  partition. See the relevant help messages for more details.
> +	  ENV_IS_IN_* options. See the relevant help messages for more details.
> +
> +config ENV_OFFSET_REDUND_RELATIVE_END
> +	bool "Offset is relative to the end of the partition"
> +	depends on SYS_REDUNDAND_ENVIRONMENT
> +	depends on ENV_IS_IN_MMC
> +	help
> +	  Treat the redundnat environment offset as relative to the end of the

s/redundnat/redundant/

> +	  MMC partition. This can be useful if your board may be fitted with
> +	  different MMC devices, which have different sizes for the MMC
> +	  partitions, and you always want the environment placed at the very end
> +	  of the partition, to leave the maximum possible space before it, to
> +	  store other data.
>   

Same remark as for ENV_OFFSET_RELATIVE_END.

Looks good to me otherwise!

Cheers,
Quentin