Re: [PATCH v4 0/5] block: partition table OF support

[Rasmus Villemoes]

Andy Shevchenko <andy@xxxxxxxxxx> writes:

> On Mon, Sep 30, 2024 at 01:30:07PM +0200, Christian Marangi wrote:
>> Hi,
>> this is an initial proposal to complete support for manually defining
>> partition table.
>> 
>> 
>> Some block device also implement boot1 and boot2 additional disk. Similar
>> to the cmdline parser, these disk can have OF support using the
>> "partitions-boot0" and "partitions-boot1" additional node.
>> 
>> It's also completed support for declaring partition as read-only as this
>> feature was introduced but never finished in the cmdline parser.
>
>
> I'm not sure I fully understood the problem you are trying to solve.
> I have a device at hand that uses eMMC (and was produced almost ten years ago).
> This device has a regular GPT on eMMC and no kernel needs to be patched for that.
> So, why is it a problem for the mentioned OEMs to use standard GPT approach?

For the user area (main block device), yes, a GPT can often be used, but
not always. For the boot partitions, the particular SOC/cpu/bootrom may
make it impossible to use a standard partition table, because the
bootrom expects to find a bootloader at offset 0 on the active boot
partition. In such a case, there's no way you can write a regular MBR or
GPT, but it is nevertheless nice to have a machine-readable definition
of which data goes where in the boot partitions. With these patches, one
can do

  partitions-boot0 {
    partition@0 {
      label = "bootloader";
      reg = <0 0x...>; // 2 MB
    }
    partition@... {
      label = "device-data";
      reg = <...> // 4 MB
    }
  }

and describe that layout.

Rasmus