[U-Boot] [RFC PATCH] arm: bootm: Boot kernel with U-Boot's FDT blob

[Alexander Graf]

On 01/10/2017 05:42 PM, york sun wrote:
> On 01/10/2017 08:35 AM, Alexander Graf wrote:
>> On 01/10/2017 05:31 PM, york sun wrote:
>>> On 01/10/2017 05:02 AM, Alexander Graf wrote:
>>>> On 01/10/2017 01:58 PM, Michal Simek wrote:
>>>>> U-Boot configured via DTB can use the same DTB for booting the kernel.
>>>>> When OF_CONTROL is used fdtcontroladdr is setup and can be use for boot.
>>>>>
>>>>> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
>>>>> ---
>>>>>
>>>>> Didn't check if there is any side effect or not but it looks weird when
>>>>> you have DT driver u-boot that you have to load dtb again.
>>>> I agree, and I think it's very reasonable to try and use the same device
>>>> tree for U-Boot and Linux.
>>>>
>>> Size is a concern. U-Boot only uses a small portion of the device tree.
>>> If the complete device tree is embedded into U-Boot, the size increases
>>> quite a bit.
>> Is size really a concern? At the end of the day we only care about the
>> full dt for non-SPL U-Boot which is reasonably big anyway. And if it's a
>> real problem, we can always compress.
>>
> Are we sure DT will never be used for SPL?

It is used for SPL today already (see firefly), but SPL can used a 
trimmed down version of device tree that only contains devices u-boot 
cares about.

> Size is an issue for MPC85xx. The reset vector is at the very end, so
> the image is fixed at 768KB for most targets (maybe some still use
> 512KB). There is limited room for additional stuff. We surely can
> increase the image size to 1MB to make room. So it is a concern but not
> a huge concern.
>
> The device tree is maintained under kernel, keeping it updated for
> U-Boot will be a challenge, won't it?

I hope it won't stay in the kernel tree forever. There have been 
discussions to move it into a separate tree for a while. On non-embedded 
devices (SPARC systems, POWER servers) device trees are *much* more 
stable than in the embedded Linux dominated world. Maybe it'll mature 
one day :).


Alex