eMMC partitions kernel comand line

eMMC partitions kernel comand line

[Giorgio Dal Molin]

Hallo,

I'm working on an arm IMX7 module with an eMMC flash on it.

I don't need/want to have a partition table on the eMMC, some hardcoded
partitions are just OK. I've already defined them in the barebox device tree
and it works, for barebox:

...
  partition@0 {
    label = "bl_env";
    reg = <BLENV_OFS BLENV_SIZE>;
  };
  partition@1 {
    label = "boot";
    reg = <BOOT_OFS BOOT_SIZE>;
  };
...

Unfortunately the same trick is not supported by the linux kernel.
What works for the kernel is the special command line option:

blkdevparts=mmcblk1:1M(bl_env),50M(boot),...

My question is: is it possible to let barebox automatically generate
this command line according to what it has in its device tree or do I
have to do it manually.

giorgio

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Re: eMMC partitions kernel comand line

[Sascha Hauer]

Hi Giorgio,

On Thu, Jun 18, 2020 at 10:21:12AM +0200, Giorgio Dal Molin wrote:
> Hallo,
> 
> I'm working on an arm IMX7 module with an eMMC flash on it.
> 
> I don't need/want to have a partition table on the eMMC, some hardcoded
> partitions are just OK. I've already defined them in the barebox device tree
> and it works, for barebox:
> 
> ...
>   partition@0 {
>     label = "bl_env";
>     reg = <BLENV_OFS BLENV_SIZE>;
>   };
>   partition@1 {
>     label = "boot";
>     reg = <BOOT_OFS BOOT_SIZE>;
>   };
> ...
> 
> Unfortunately the same trick is not supported by the linux kernel.
> What works for the kernel is the special command line option:
> 
> blkdevparts=mmcblk1:1M(bl_env),50M(boot),...
> 
> My question is: is it possible to let barebox automatically generate
> this command line according to what it has in its device tree or do I
> have to do it manually.

No, this is currently not possible, at least not without adding this
feature to barebox. Note that barebox doesn't know which MMC device
corresponds to "mmcblk1" as it depends on the initialization order in
Linux which MMC ends up as "mmcblk1".

It might be worth trying to add device tree partitioning support for
MMCs to Linux. The command line option was accepted also, so why not
device tree?

Regards,
  Sascha

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