[U-Boot] [PATCH 14/18] efi: stub: Pass EFI GOP information to U-Boot payload

[Alexander Graf]

On 06/11/2018 08:01 AM, Bin Meng wrote:
> Hi Alex,
>
> On Mon, Jun 11, 2018 at 1:52 PM, Alexander Graf <agraf at suse.de> wrote:
>>
>> On 11.06.18 01:29, Bin Meng wrote:
>>> On Mon, Jun 11, 2018 at 3:16 AM, Alexander Graf <agraf at suse.de> wrote:
>>>>
>>>> On 10.06.18 15:25, Bin Meng wrote:
>>>>> If UEFI BIOS has the graphics output protocol (GOP), let's pass its
>>>>> information to U-Boot payload so that U-Boot can utilize it (eg:
>>>>> an EFI framebuffer driver).
>>>>>
>>>>> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
>>>> Why can't the FB drive determine all of this on its own and just fail
>>>> probe if no GOP protocol can be found?
>>>>
>>> It cannot. Once U-Boot payload is running, the boot services are gone.
>>> There is no way to determine the GOP protocol.
>> Interesting. Is there a particular reason you're not preserving boot
>> services?
>>
> This is EFI payload support with CONFIG_EFI_STUB. Preserving boot
> services is EFI application, with CONFIG_EFI_APP. For example, see
> serial_efi.c which is the serial driver that uses EFI's boot services
> to output characters on the serial port.

Oh, I see. That makes sense now.

Do people actually need CONFIG_EFI_STUB then?

>
>> It might be quite handy to reuse UEFI block interfaces for example. It
>> might also be useful to preserve (parts of?) the memory map so we don't
>> overwrite random SMM code for example.
>>
>> Maybe I misunderstand the purpose of the UEFI U-Boot support though ;).
> Looks there is some misunderstanding around the EFI payload support.

Yes, I have to admit that I never really cared enough about it to read 
its documentation though :).


Alex