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

[Takashi Iwai]

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.


thanks,

Takashi