[U-Boot] [PATCH] efi: Update README.efi to clarify build and test instructions

[Bin Meng]

Hi Igor,

On Fri, Aug 14, 2015 at 9:03 PM, Stoppa, Igor <igor.stoppa at intel.com> wrote:
> Hi Bin,
>
> On 14 August 2015 at 15:54, Bin Meng <bmeng.cn at gmail.com> wrote:
>> Hi Igor,
>>
>> On Fri, Aug 14, 2015 at 8:46 PM, Stoppa, Igor <igor.stoppa at intel.com> wrote:
>
> [...]
>
>>> Yes, I did read it. That section is - unsurprisingly - written from
>>> the perspective of a U-Boot developer/user.
>>
>> Yes, they are for hackers.
>
> Heh, nice answer, yet my observation was on the lines of:
>
> "written from the perspective of a U-Boot developer/user vs the
> perspective of an EFI developer/user"
>
> IOW it was not clear to me if the jargon EFI payload / EFI app was
> limited to the U-Boot world or not. Now I know that it is :-)
>
> [...]
>
>> Oops, I misread. Do you mean the console output from U-Boot
>> application and payload?
>
> yes, at least in the stub.c file it is clearly visible that the
> console output can be routed either to the serial port or to the
> screen.

At the stub phase, it is still the EFI application phase, and U-Boot
uses EFI console output protocol to print messages. If you read the
hacker part, it is already documented. Or maybe if you are familiar
with EFI, at this stage it is still under EFI control so you may be
seeing either serial or display or both. After exit boot services
call, EFI no longer control the system and it is solely a U-Boot
payload running so which console output depends on U-Boot driver
support in that payload.

>
> It might be worth mentioning under which circumstances this happen in
> a certain way and under which circumstances it happen in another way,
> if it's something that is specific to EFI.
>

Does this really matter? An example would be: when I boot Linux I may
get part of the kernel output on the serial and the other part on the
screen, or maybe nothing. But finally I know it's booting, that's
enough. But if I want to figure out *when* this switch happens I may
have to dig into the source codes. After all, it is open source and
you can read it by yourself :-)

Regards,
Bin