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

[york sun]

On 11/21/2016 01:07 PM, Alexander Graf wrote:
>
>
> 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,

Since you are most familiar with EFI boot code, can you send a patch to 
address this? I can squash it with Alison's patch after testing. My 
current test branch is 
http://git.denx.de/?p=u-boot/u-boot-fsl-qoriq.git;a=shortlog;h=refs/heads/test_qoriq.

Thanks.

York