[RFC 6/7] ARM: vf610m4: HACK: get dtb pointer from SRC_GPR3

[Stefan Agner]

Am 2014-10-12 21:00, schrieb Arnd Bergmann:
> On Sunday 12 October 2014 20:14:00 Stefan Agner wrote:
>> Get DTB pointer (located in r2) from SRC_GPR3 (argument register
>> for secondary core)
>>
>> Signed-off-by: Stefan Agner <stefan at agner.ch>
>> ---
>> This is clearly a hack but it works around the need of a boot loader
>> on the Cortex-M4. I guess there is no way neither its acceptable to
>> do this on machine level..? But then, this can also be done with a
>> minimal boot loader loaded just in front of the kernel by the m4boot
>> utility.
>>
> 
> How do you actually enter the kernel on the m4? Do you use a
> decompressor or XIP_KERNEL at the moment? There are probably 
> lots of ways to do this, my first idea would be to have a vybrid
> specific boot wrapper that consists of just a few assembly
> instructions to set up the initial environment from wherever
> it gets started.

I use the XIP_KERNEL at the moment. There is a special memory area which
can be accessed through code bus of the Cortex-M4 (the ARM-v7m
architecture has two buses to the CPU, one for data, one for code. On
Vybrid you can distinguish between those two buses by using different
memory areas). So in order to make use of the Code bus, I would like to
place the kernel there, XIP kernel probably the easiest way to do
this...

--
Stefan