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

[Lyude Paul <lyude@redhat.com>]

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!

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.

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