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

[Christian König]

Am 03.04.2018 um 10:36 schrieb Michel Dänzer:
> On 2018-04-01 07:45 PM, Ilia Mirkin wrote:
>> On Sun, Apr 1, 2018 at 1:39 PM, Christian König
>> <christian.koenig at amd.com> wrote:
>>> Am 30.03.2018 um 22:45 schrieb Takashi Iwai:
>>>> 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.
>>>
>>> NAK, modesetting is mandatory for amdgpu and we should probably remove the
>>> option to disable it from other DRM drivers without UMS support as well
>>> (pretty much all of them now).
>>>
>>> If you want to prevent a driver from loading I think the correct way to do
>>> so is to give modprobe.blacklist=amdgpu on the kernel commandline.
>>>
>>> That would remove the possibility to prevent the driver from loading when it
>>> is compiled in, but I don't see much of a problem with that.
>> Having a way to kill the graphics driver is a very useful debugging
>> tool, and also a quick and easy way to get out of an unpleasant
>> situation where graphics are messed up / system hangs / etc. The
>> modprobe blacklist kernel arg only works in certain environments (and
>> only if it's a module).
> Building amdgpu into the kernel isn't feasible for a generic kernel such
> as a distro one, because it would require including all microcode into
> the kernel as well (12M right now, and growing).
>
> If a user decides to build amdgpu into their custom kernel and runs into
> trouble due to that, that's "doctor, it hurts if I do this" territory.

Correct, but I agree that even in this situation it would be very 
helpful to prevent the gfx drivers from loading and fallback to 
efifb/vesafd (or whatever the platform provides).

It's just that the "nomodeset" and "amdgpu.modeset=0" options are really 
not well named for this task.

Christian.