BCM2836 (Raspberry Pi 2) port

Stephen Warren [off-list ref] writes:

On 05/12/2015 11:32 AM, Eric Anholt wrote:

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Stephen Warren [off-list ref] writes:

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On 05/12/2015 09:39 AM, Alexander Stein wrote:

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On Monday 11 May 2015, 20:36:40 wrote Stephen Warren:

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On 05/08/2015 10:14 AM, Alexander Stein wrote:

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On Thursday 23 April 2015, 22:25:08 wrote Stephen Warren:

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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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