Re: [PATCH] drm/amdgpu: Add 'modeset' module parameter

[Christian König]

Am 11.05.22 um 20:36 schrieb Alex Deucher:
> On Wed, May 11, 2022 at 2:20 PM Lyude Paul <lyude@xxxxxxxxxx> wrote:
> > Many DRM drivers feature a 'modeset' argument, which can be used to
> > enable/disable the entire driver (as opposed to passing nomodeset to the
> > kernel, which would disable modesetting globally and make it difficult to
> > load amdgpu afterwards). Apparently amdgpu is actually missing this
> > however, so let's add it!
> You can already do that by passing modprobe.blacklist=amdgpu on the
> kernel command line.  I don't think we need another option to do that.

Yeah, this already came up multiple times and so far we have always 
rejected it.

Stuffing that into drivers is not a good approach I think. If we want to 
prevent some device from exposing it's display functionalities we should 
rather push that into the drm layer.

Regards,
Christian.

> > Keep in mind that this currently just lets one enable or disable amdgpu, I
> > haven't bothered adding a headless mode like nouveau has - however I'm sure
> > someone else can add this if needed.
> You can do this as well by passing an IP block mask which disables the
> display IP, or media IP, etc.
>
> Alex
>
> > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > index ebd37fb19cdb..24e6fb4517cc 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > @@ -872,6 +872,15 @@ MODULE_PARM_DESC(smu_pptable_id,
> >          "specify pptable id to be used (-1 = auto(default) value, 0 = use pptable from vbios, > 0 = soft pptable id)");
> >   module_param_named(smu_pptable_id, amdgpu_smu_pptable_id, int, 0444);
> >
> > +/**
> > + * DOC: modeset (int)
> > + * Used to enable/disable modesetting for amdgpu exclusively.
> > + */
> > +bool amdgpu_enable_modeset = true;
> > +MODULE_PARM_DESC(modeset,
> > +                "Enable or disable display driver (1 = on (default), 0 = off");
> > +module_param_named(modeset, amdgpu_enable_modeset, bool, 0444);
> > +
> >   /* These devices are not supported by amdgpu.
> >    * They are supported by the mach64, r128, radeon drivers
> >    */
> > @@ -2003,6 +2012,11 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
> >          bool is_fw_fb;
> >          resource_size_t base, size;
> >
> > +       if (!amdgpu_enable_modeset) {
> > +               DRM_INFO("modeset=0 passed to amdgpu, driver will not be enabled\n");
> > +               return -ENODEV;
> > +       }
> > +
> >          /* skip devices which are owned by radeon */
> >          for (i = 0; i < ARRAY_SIZE(amdgpu_unsupported_pciidlist); i++) {
> >                  if (amdgpu_unsupported_pciidlist[i] == pdev->device)
> > --
> > 2.35.1