[PATCH 2/2] drm/amdgpu: Add modeset module option

[Koenig, Christian]

Am 25.09.19 um 10:07 schrieb Dave Airlie:
> On Sat, 31 Mar 2018 at 06:45, Takashi Iwai <tiwai at suse.de> wrote:
>> amdgpu driver lacks of modeset module option other drm drivers provide
>> for enforcing or disabling the driver load.  Interestingly, the
>> amdgpu_mode variable declaration is already found in the header file,
>> but the actual implementation seems to have been forgotten.
>>
>> This patch adds the missing piece.
> I'd like to land this patch, I realise people have NAKed it but for
> consistency across drivers I'm going to ask we land it or something
> like it.
>
> The main use case for this is actually where you have amdgpu crashes
> on load, and you want to debug them, people boot with nomodeset and
> then modprobe amdgpu modeset=1 to get the crash in a running system.
> This works for numerous other drivers, I'm not sure why amdgpu needs
> to be the odd one out.

Because this is essentially the wrong approach.

The correct way to prevent a module from automatically loading is to add 
modprobe.blacklist=$name to the kernel command line.

The modeset and nomodeset kernel options where used to switch between 
KMS and UMS and not to disable driver load.

We should have removed those options with the removal of UMS or 
otherwise it becomes just another ancient cruft we need to carry forward 
in potentially all drivers.

Regards,
Christian.

>
> Reviewed-by: Dave Airlie <airlied at redhat.com>
>
> Dave.