Development tree for Cortex-A15?

[Marc Zyngier]

On Fri, 4 May 2012 15:30:27 +0100 (BST), Jemma Jones
<jemmajones81 at yahoo.co.uk> wrote:
>> Subject: Re: Development tree for Cortex-A15?
> 
>> 
>> On Fri, 4 May 2012 09:44:07 +0100 (BST), Jemma Jones
>> <jemmajones81 at yahoo.co.uk> wrote:
>>>>  Subject: Re: Development tree for Cortex-A15?
>>> 
>>>> 
>>>>  On Thu, 3 May 2012 14:35:55 +0100 (BST), Jemma Jones
>>>>  <jemmajones81 at yahoo.co.uk> wrote:
>>>>>>   Subject: Re: Development tree for Cortex-A15?
>>>>> 
>>>>>   I'm currently on kvm-arm-v7-ael, because it looked like the 
>> most
>>>>>   up-to-date one. Which one should I be using for Cortex-A15 
>> support?
>>>> 
>>>>  That branch is good enough, if you have a bleeding edge QEMU. Note
>>>>  that
>>>>  the VE A15 support in that tree is DT only. I'm working on a v3.4 
>> based
>>>>  one
>>>>  at the moment, but that's not completely ready yet.
>>> 
>>>  I'm just a little confused because under arch/arm/mach-vexpress/
there
>> is
>>>  no A15 tile? On the virtualopensystems.com git (which you quote
above)
>> you
>>>  had to explicitly enable the board and it would show up in the
.config
>> as
>>>  CONFIG_ARCH_VEXPRESS_CA15X4. Is that not the case anymore in your
>>>  kernel
>>>  tree?
>> 
>> No. The ARM tree in general is moving to the device tree, and
>> CONFIG_ARCH_VEXPRESS_CA15X4 was always meant as a temporary hack until
>> the
>> VE-DT port was mature enough to be used.
>> 
>> As Paweł's DT work has been merged into 3.4, there is strictly no
reason
>> to keep this hack around, and my recent trees do reflect that fact
>> (kvm-arm-v7-ael and kvm-arm-3.4). Christoffer may decide to keep this
in
>> his tree during a transition period, but CONFIG_ARCH_VEXPRESS_CA15X4 is
>> dead as far as I am concerned.
>> 
>> If you're just starting to play with KVM-ARM now, please don't rely on 
>> the
>> A15 board file, it is a dead end.
> 
> What would be the correct configuration of low-level kernel debugging
for
> the A15 board? I'd like to have earlyprintk etc working.
> 
> When I set it to 
> Kernel low-level debugging port (No low-level debugging UART)
> 
> then I get the following error:
> 
> $ ARCH=arm make uImage
> scripts/kconfig/conf --silentoldconfig Kconfig
> #
> # configuration written to .config
> #
>   CHK     include/linux/version.h
>   CHK     include/generated/utsrelease.h
> make[1]: `include/generated/mach-types.h' is up to date.
>   CALL    scripts/checksyscalls.sh
>   CHK     include/generated/compile.h
>   AS      arch/arm/kernel/debug.o
> In file included from arch/arm/kernel/debug.S:104:0:
> arch/arm/mach-vexpress/include/mach/debug-macro.S:26:2: error: #error
> "Unknown vexpress UART offset"
> make[1]: *** [arch/arm/kernel/debug.o] Error 1
> make: *** [arch/arm/kernel] Error 2

Known problem with this kernel tree, fixed in kvm-arm-3.4.

> If I just disable
> [*] Kernel low-level debugging functions
> then I don't seem to get any output at all.

Because your kernel is probably crashing before the console is enabled.

> What is the correct configuration?

First, we have to understand why your kernel is crashing, and I have the
strong feeling it is DT related. I'm really curious of what dts file you're
using when building your uImage...

        M.
-- 
Fast, cheap, reliable. Pick two.