[U-Boot] [PATCH v5 1/2] armv8: Support loading 32-bit OS in AArch32 execution state

[Alexander Graf]

On 07/07/2016 02:46 PM, Ryan Harkin wrote:
> On 7 July 2016 at 13:41, Alexander Graf <agraf at suse.de> wrote:
>> On 07/07/2016 02:35 PM, Ryan Harkin wrote:
>>> On 7 July 2016 at 13:30, Alexander Graf <agraf at suse.de> wrote:
>>>> On 07/07/2016 02:16 PM, Ryan Harkin wrote:
>>>>> On 7 July 2016 at 07:30, Alison Wang <b18965 at freescale.com> wrote:
>>>>>> To support loading a 32-bit OS, the execution state will change from
>>>>>> AArch64 to AArch32 when jumping to kernel.
>>>>>>
>>>>>> The architecture information will be got through checking FIT image,
>>>>>> then U-Boot will load 32-bit OS or 64-bit OS automatically.
>>>>>>
>>>>>> Signed-off-by: Ebony Zhu <ebony.zhu at nxp.com>
>>>>>> Signed-off-by: Alison Wang <alison.wang at nxp.com>
>>>>>> Signed-off-by: Chenhui Zhao <chenhui.zhao at nxp.com>
>>>>> Unfortunately, this patch fails to boot for me.
>>>>>
>>>>> On FVP Foundation models, I see this error before the model hangs:
>>>>>
>>>>> [snip]
>>>>> Starting kernel ...
>>>>>
>>>>> resetting ...
>>>>> [snip]
>>>>>
>>>>> And I see the same output on AEMv8 Base models and Juno boards, only
>>>>> they reset continuously rather than hang.
>>>>>
>>>>> I think the problem is that I see this from ARM Trusted Firmware on
>>>>> boot:
>>>>>
>>>>> INFO:    BL31: Preparing for EL3 exit to normal world
>>>>>
>>>>> Looking at the patch, it appears to be changing everything to boot in
>>>>> EL2.
>>>>
>>>> That was the case before the patch (with the removal of the EL1 boot
>>>> thing)
>>>> already. Linux can't run in EL3, that's why it has to boot in EL2 (or
>>>> EL1,
>>>> but that really should be limited to VMs).
>>>>
>>> Pah!  I misread the patch, specifically this hunk (and the one before
>>> it, I suppose):
>>>
>>> diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
>>> index e3c9832..59adab8 100644
>>> --- a/arch/arm/lib/bootm.c
>>> +++ b/arch/arm/lib/bootm.c
>>> @@ -193,7 +193,6 @@ static void do_nonsec_virt_switch(void)
>>>    {
>>>        smp_kick_all_cpus();
>>>        dcache_disable();    /* flush cache before swtiching to EL2 */
>>> -    armv8_switch_to_el2();
>>>    }
>>>    #endif
>>>
>>> That's a "-", not a "+" on the call to armv8_switch_to_el2().
>>>
>>> Either way, all my platforms are dead with this patch.
>>
>> Since you're running in software models, can you try to figure out where
>> exactly it breaks?
> You assume that because I have a model that I have the ability to debug it ;-)
>
> ARM's FVP Foundation model is publicly available and free to use.  So
> if you want to give it a spin, it's there for the taking.

I thought the Foundation model doesn't support external debugging? I'd 
basically want to put a breakpoint at the point where the kernel exit 
print goes and then trace it from there :).

But since Alison wrote the patches, I'm sure he can do that too :).


Alex