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

["Christian König" <christian.koenig@amd.com>]

Am 11.05.22 um 20:36 schrieb Alex Deucher:
> On Wed, May 11, 2022 at 2:20 PM Lyude Paul <lyude@redhat.com> 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@redhat.com>
>> ---
>>   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
>>