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

[Michel Dänzer]

On 2018-04-03 11:02 AM, Takashi Iwai wrote:
> On Tue, 03 Apr 2018 10:57:56 +0200,
> Christian K6nig wrote:
>>
>> 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.
> 
> Agreed with the naming mess.  But OTOH, it's already a thing that is
> too popular to kill.  You can add a more suitable option name, but you
> cannot drop these existing ones easily.  It's already in a gray zone
> of the golden "don't break user-space" rule.

That's quite a stretch argument, given that amdgpu has never supported
the modeset parameter. Also, module parameters aren't UAPI.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer