[U-Boot] [PATCH v8 1/3] armv8: Support loading 32-bit OS in AArch32 execution state

[york sun]

On 11/21/2016 12:40 PM, Alexander Graf wrote:
>
>
> On 21/11/2016 21:23, york sun wrote:
>> On 11/09/2016 07:02 PM, Alison Wang 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>
>>> ---
>>> Changes in v8:
>>> - Fix the issue when U-Boot is running in EL2 or EL1.
>>>
>>
>> Alison,
>>
>> There is a conflict when merging with upstream code. Alex Graf merged
>> his change to support EFI booting. See commit
>> 69bd459d343fe1e5a68a6f187d8c99c78c6fc6ce. Specifically these lines
>>
>>
>>          if (current_el() == 3) {
>>                  smp_kick_all_cpus();
>>                  dcache_disable();
>>                  armv8_switch_to_el2();
>>                  dcache_enable();
>>          }
>>
>> Function armv8_switch_to_el2() didn't take any argument before you
>> change. With your proposed change to support 32-bit OS, you added
>> arguments to this function, and presume this function always load OS.
>> This may be flawed. Would it be possible to keep armv8_switch_to_el2()
>> but introduce another function to carry out switching EL while loading OS?
>
> Alison introduced it based on my comments - and I'd prefer if we only
> have the function call based version :).
>
> It should be reasonably straight forward to move to it here. Just create
> a new helper stub that enables the dcache and calls entry().
>

Alex,

Do you always load OS when calling armv8_switch_to_el2()? In this case 
of efi booting, kernel entry point needs to be passed to the new 
armv8_switch_to_el2 function. The new armv8_switch_to_el2 function 
doesn't return, so you cannot continue to run the code.

York