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

[Ryan Harkin]

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'm slightly confused that it's resetting. The switch to
> EL2 shouldn't matter in your setup, because you're executing U-Boot in EL2
> already, since you're running ATF in EL3.
>
>
> Alex
>