[U-Boot] CONFIG_MIPS_BOOT_CMDLINE_LEGACY usage ?

[Stefan Roese]

On 15.08.2018 16:05, Daniel Schwierzeck wrote:
> 
> 
> On 15.08.2018 15:13, Stefan Roese wrote:
>> Hi Daniel,
>>
>> On 15.08.2018 15:01, Daniel Schwierzeck wrote:
>>> On 15.08.2018 10:23, Stefan Roese wrote:
>>>> Hi Daniel,
>>>>
>>>> I'm wondering about the CONFIG_MIPS_BOOT_CMDLINE_LEGACY Kconfig
>>>> option in MIPS. Why is this one called "legacy" and what should
>>>> be used instead to pass the U-Boot bootargs to the Linux kernel?
>>>>
>>>> Thanks,
>>>> Stefan
>>>
>>> This interface was initially added to U-Boot with MIPS support and is
>>> copied from the MIPS Yamon bootloader. Dependent on the platform and the
>>> used bootloader there are more different boot interfaces.
>>>
>>> The modern way to boot a kernel on MIPS would be to add a DTB to the
>>> kernel FIT image and let U-Boot pass it over to the kernel
>>> (CONFIG_MIPS_BOOT_FDT). All bootargs would then be added automatically
>>> to the /chosen/bootargs node. This interface is conformant with the MIPS
>>> UHI boot protocol. The kernel supports this in a generic way. The PROM
>>> code of a platform only needs to evaluate the fw_passed_dtb variable for
>>> a DTB address. In your case the Ralink platform supports this.
>>>
>>> But you still have the flexibility to use a DTB built-in or appended to
>>> the kernel and pass the bootargs in the traditional way. The kernel has
>>> various config options to select the source of bootargs.
>>
>> I see. Thanks for the detailed answer. We'll move over to passing via
>> DT once this is ready in Linux. Until then, we will use this legacy
>> interface.
>>
> 
> DT handover is already supported for Ralink/mMediatek platform, see [1]
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/mips/ralink/of.c#n78

Right, thanks. I was more referring to the fact, that the current
Linux target we are using is not using an separate DT blob. Its no
big deal to add this though and we will do this soon.

Thanks,
Stefan