[PATCH V2] ARM: mvebu: fix RAM size for Armada XP board DB-MV784MP-GP

[Gregory CLEMENT]

On 03/14/2013 05:56 PM, Jason Cooper wrote:
> On Thu, Mar 14, 2013 at 10:22:36AM -0600, Jason Gunthorpe wrote:
>> On Thu, Mar 14, 2013 at 03:57:54PM +0000, Jason Cooper wrote:
>>> The board is supplied with a 4GB RAM module.  This value can be
>>> overridden by the bootloader based on probed memory size.  We set it to
>>> a reasonable value here.
>>>
>>> Signed-off-by: Jason Cooper <jason at lakedaemon.net>
>>> Changes from v1:
>>>  - grammatical fix suggested by Sergei Shtylyov
>>>  - correct size suggested by several folks (within 32bit, 1 dword)
>>>
>>> As promised, catching this fix in the -rc cycle.
>>>
>>> For those not familiar, earlier versions of the patch adding this board listed
>>> 3GB because that is all that was visible.  I mistaken applied v3 of the patch
>>> instead of v4 which properly listed 4GB.  This patch cleans up my error.
>>
>> What happens when the kernel tries to treat 0xD0000000 and above as
>> memory? Lots of internal register blocks overlap 0 -> 4GB - won't this
>> cause resource conflicts on boot? I'm actually very surprised it boots
>> at all - what does /proc/iomem say?
> 
> We'll have to wait to hear from Gregory or Florian on that.  They are
> the only two I know of who have this board.  I can only compile-test.
> 

Indeed there are conflicts with the internals registers. I was too focused
on the size of the RAM itslelf and I forgotten that if we use the 4GB we have
no more address space for the internal registers themselves.
Even with LPAE we will need to leave a "hole" from 0xD0000000 to 0x100000000
for these registers.

So to conclude, currently, if we try to boot the Armada XP GP board with
reg = <0x00000000 0xFFFFFFFF>, the kernel crash, even if there is 4GB of
RAM.

> thx,
> 
> Jason.
> 


-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com