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

[york sun]

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?

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?

York