drm/amdgpu/uvd4.2: Don't initialize UVD 4.2 when DPM is disabled

[ Upstream commit 8b3e8fa ]

UVD 4.2 doesn't work at all when DPM is disabled because
the SMU is responsible for ungating it. So, Linux fails
to boot with CIK GPUs when using the amdgpu.dpm=0 parameter.

Fix this by returning -ENOENT from uvd_v4_2_early_init()
when amdgpu_dpm isn't enabled.

Note: amdgpu.dpm=0 is often suggested as a workaround
for issues and is useful for debugging.

Fixes: a2e73f5 ("drm/amdgpu: Add support for CIK parts")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Timur Kristóf

drivers/gpu/drm/amd/amdgpu/uvd_v4_2.c

@@ -93,6 +93,11 @@ static void uvd_v4_2_ring_set_wptr(struct amdgpu_ring *ring)
 static int uvd_v4_2_early_init(struct amdgpu_ip_block *ip_block)
 {
 	struct amdgpu_device *adev = ip_block->adev;
+
+	/* UVD doesn't work without DPM, it needs DPM to ungate it. */
+	if (!amdgpu_dpm)
+		return -ENOENT;
+
 	adev->uvd.num_uvd_inst = 1;
 
 	uvd_v4_2_set_ring_funcs(adev);