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

[Alexander Graf]

On 21/11/2016 21:45, york sun wrote:
> 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.

We always call some random function pointer in the new flow. That can be 
a kernel entry point, but it can also just be a function pointer. In 
this case, the code would basically look like this:

static ulong efi_run_in_el2(ulong (*entry), void *arg1, void *arg2)
{
     dcache_enable();
     return entry(arg1, arg2);
}

if (current_el() == 3) {
     ...
     return armv8_switch_to_el2(efi_run_in_el2, entry, 
&loaded_image_info, &systab);
}


Alex