BCM2836 (Raspberry Pi 2) port

Eric Anholt eric at anholt.net
Wed May 13 10:46:24 PDT 2015

Stephen Warren <swarren at wwwdotorg.org> writes:

> On 05/12/2015 11:32 AM, Eric Anholt wrote:
>> Stephen Warren <swarren at wwwdotorg.org> writes:
>>> On 05/12/2015 09:39 AM, Alexander Stein wrote:
>>>> On Monday 11 May 2015, 20:36:40 wrote Stephen Warren:
>>>>> On 05/08/2015 10:14 AM, Alexander Stein wrote:
>>>>>> On Thursday 23 April 2015, 22:25:08 wrote Stephen Warren:
>>>>>>>> Hit any key to stop autoboot:  0
>>>>>>>> U-Boot> setenv fdt_high fffffff
>>>>>> Any specific reason to set fdt_high to fffffff?
>>>>> Yes, it prevents U-Boot's annoying habit of moving the DTB from where it
>>>>> was loaded to some other place. This was especially important in this
>>>>> case since I was trying to find out exactly which piece of RAM being
>>>>> over-written caused the issues I was seeing.
>>>> Shouldn't this then be part of the default raspberry (2 only?) environment?
>>> Eventually yes. So far, nobody seems to know which areas of RAM are
>>> off-limits (presumably since the RAM is used as a CPU1..3 pen), so I was
>>> experimenting to try and find that out.
>> If I'm reading this right, the CPU1-3 pen is in the bottom 8k of memory
>> (actually much less than 8k).
> Hmm. I wondered if that was the case. I don't think anything I was doing 
> in U-Boot /should/ touch those pages, but there have been bugs before 
> where some pointer was left at NULL, and some DM (U-Boot Device Model) 
> code ended up putting structures in page 0 by mistake. Perhaps something 
> like that has resurfaced. I'll try to find time to diff page 0 
> before/after various U-Boot operations, and see if it's getting modified...

How about on the Linux side?  What's reserving that memory for us, if
anything?  Weird things happen if I put "ARM: bcm2836: Add a DT binding
for the ARM local registers." and "ARM: bcm2835: Use a syscon regmap to
set up timer frequency." before the SMP support in the bcm2836-smp tree
(init crashes).
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