[U-Boot] can u-boot tools fw_{printenv, setenv} work with eMMC HW partition?

[Michael Heimpold <mhei@heimpold.de>]

Hi,

>   right, i can see that and that clarifies things for me. my
> *original* question was whether there was a way to set up
> /etc/fw_env.config to refer to the eMMC partition /dev/mmcblk1boot1
> *directly*, treating it as a regular block partition and bypassing all
> the MTD-related processing. (perhaps stefano can weigh in and say
> whether that's how he understood what i was asking.)
> 
>   if you instead refer to /dev/mmcblk1, as i understand it, you're
> just back to the standard MTD-based access, yes?

the /dev/mmcblk... devices are block devices and do not provide
the MTD API of the kernel. I guess this is the cause for the error message
you've seen. You could try strace to verify.
And this is the problem why the patches Luka mentioned are required:
they make fw_{printenv,setenv} aware of opening such block devices
by-passing the MTD-specific stuff, that means simply open the file,
write/read the data and close the file descriptor. Without these patches
these tools assume that the file descriptor opened are MTD-based.

You can pass what ever you want via your config, so your file could
look like:
/dev/mmcblk1boot1 0x0 0x4000
Since the partition is somewhere placed on the eMMC device, you
can also refer to the same location using /dev/mmcblk1. In the latter
case you have to calculate the offset correctly to not overwrite
other data (e.g. on other partitions). Using /dev/mmcblk1boot1 as
"entry point" the kernel should reject write requests which go beyond
the partition size.

BR, Michael