[U-Boot] [PATCH 2/2] boards: ls2080: Disable fdt copying by default

[york sun]

On 03/01/2016 09:35 AM, Scott Wood wrote:
> On Tue, 2016-03-01 at 16:48 +0000, york sun wrote:
>> On 03/01/2016 08:01 AM, Scott Wood wrote:
>>> On Tue, 2016-03-01 at 06:03 +0000, Bhupesh Sharma wrote:
>>>>> From: york sun
>>>>> Sent: Tuesday, March 01, 2016 11:30 AM
>>>>>
>>>>> On 02/29/2016 09:20 PM, Bhupesh Sharma wrote:
>>>>>>> From: U-Boot [mailto:u-boot-bounces at lists.denx.de] On Behalf Of
>>>>>>> Scott
>>>>>>> Wood
>>>>>>> Sent: Tuesday, March 01, 2016 7:13 AM
>>>>>>>
>>>>>>> On Tue, 2016-03-01 at 00:08 +0000, york sun wrote:
>>>>>>>> Sorry for top posting. I am on outlook web access.
>>>>>>>>
>>>>>>>> There may be some limitation on fdt relocation. Without setting
>>>>>>>> fdt_high, u -boot relocates the device tree toward the end of
>>>>>>>> useable memory. I haven't got a chance to debug why it doesn't
>>>>>>>> work.
>>>>>>>>
>>>>>>>> This patch is to disable the relocation by default. A magic
>>>>>>>> number
>>>>>>>> 0xa0000000 doesn't make much sense here.
>>>>>>>
>>>>>>> I agree, if the number is arbitrary.  But if Linux has a
>>>>>>> limitation,
>>>>>>> as it does on arm32, then it should be expressed here.
>>>>>>>
>>>>>>
>>>>>> There are explicit requirements for placement of DTB for aarch64
>>>>>> linux.
>>>>>> Linux versions prior to v4.2 also require that the DTB be placed
>>>>>> within the 512 MB region starting at text_offset bytes below the
>>>>>> kernel
>>>>> Image:
>>>>>>
>>>>>> http://lxr.free-electrons.com/source/Documentation/arm64/booting.txt
>>>>>> #L
>>>>>> 43
>>>>>>
>>>>>> York - have you tested this patch against older kernels like 3.18?
>>>>>
>>>>> Bhupesh,
>>>>>
>>>>> Thanks for the link. It may explained why Linux doesn't boot if
>>>>> fdt_high
>>>>> is not set properly on kernel prior 4.2.
>>>>>
>>>>> I proposed to disable fdt copying by default. It doesn't mean we
>>>>> cannot
>>>>> will won't use fdt_high. My point is, setting an arbitrary value
>>>>> doesn't
>>>>> make much sense.
>>>
>>> It's not arbitrary if it comes from a Linux requirement.
>>
>> Even kernel requires device tree to be within 512MB from kernel image, it
>> doesn't warrant a magic number, because the kernel image location is not
>> fixed.
> 
> It's not "512MB from kernel image".  It's "within the 512 MB region starting
> at text_offset bytes below the kernel Image" which, when combined with "The
> Image must be placed text_offset bytes from a 2MB aligned base address near
> the start of usable system RAM and called there" means that if RAM starts at
> 0x80000000, the actual limit is "near" (and no lower than) 0xa0000000, which
> makes 0xa0000000 a good default.

I get your point. Basically you expect U-Boot has default setting for a default
use, and you expect U-Boot knows the exact memory location and size. It is
reasonable.

I was debugging high region memory. I have to abandon low region all together so
Linux can boot from high region memory.

I can drop this patch for now and revisit it when we decide to move to high
region memory.

York