Reuse framebuffer after a kexec (amdgpu / efifb)

[Felix Kuehling]

On 2021-12-10 10:13 a.m., Christian König wrote:
>
>
> Am 10.12.21 um 15:25 schrieb Guilherme G. Piccoli:
>> On 10/12/2021 11:16, Alex Deucher wrote:> [...]
>>> Why not just reload the driver after kexec?
>>>
>>> Alex
>> Because the original issue is the kdump case, and we want a very very
>> tiny kernel - also, the crash originally could have been caused by
>> amdgpu itself, so if it's a GPU issue, we don't want to mess with that
>> in kdump. And I confess I tried modprobe amdgpu after a kdump, no
>> success - kdump won't call shutdown handlers, so GPU will be in a
>> "rogue" state...
>>
>> My question was about regular kexec because it's much simpler usually,
>> we can do whatever we want there. My line of thought was: if I make it
>> work in regular kexec with a simple framebuffer, I might be able to get
>> it working on kdump heheh
>
> How about issuing a PCIe reset and re-initializing the ASIC with just 
> the VBIOS?
>
> That should be pretty straightforward I think.

Do you actually need to restore the exact boot-up mode? If you have the 
same framebuffer memory layout (width, height, bpp, stride) the precise 
display timing doesn't really matter. So we "just" need to switch to a 
mode that's compatible with the efifb framebuffer parameters and point 
the display engine at the efifb as the scan-out buffer.

Regards,
   Felix


>
> Christian.