[PATCH v4] drm/amd/amdgpu: Prevent null pointer dereference in GPU bandwidth calculation

[Srinivasan Shanmugam]

If the parent is NULL, adev->pdev is used to retrieve the PCIe speed and
width, ensuring that  the function can still determine these
capabilities from the device itself.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:6193 amdgpu_device_gpu_bandwidth()
	error: we previously assumed 'parent' could be null (see line 6180)

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
    6170 static void amdgpu_device_gpu_bandwidth(struct amdgpu_device *adev,
    6171                                         enum pci_bus_speed *speed,
    6172                                         enum pcie_link_width *width)
    6173 {
    6174         struct pci_dev *parent = adev->pdev;
    6175
    6176         if (!speed || !width)
    6177                 return;
    6178
    6179         parent = pci_upstream_bridge(parent);
    6180         if (parent && parent->vendor == PCI_VENDOR_ID_ATI) {
                     ^^^^^^
If parent is NULL

    6181                 /* use the upstream/downstream switches internal to dGPU */
    6182                 *speed = pcie_get_speed_cap(parent);
    6183                 *width = pcie_get_width_cap(parent);
    6184                 while ((parent = pci_upstream_bridge(parent))) {
    6185                         if (parent->vendor == PCI_VENDOR_ID_ATI) {
    6186                                 /* use the upstream/downstream switches internal to dGPU */
    6187                                 *speed = pcie_get_speed_cap(parent);
    6188                                 *width = pcie_get_width_cap(parent);
    6189                         }
    6190                 }
    6191         } else {
    6192                 /* use the device itself */
--> 6193                 *speed = pcie_get_speed_cap(parent);
                                                     ^^^^^^ Then we are toasted here.

    6194                 *width = pcie_get_width_cap(parent);
    6195         }
    6196 }

Fixes: 9e424a5d9087 ("drm/amdgpu: cache gpu pcie link width")
Cc: Christian König <christian.koenig at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
Suggested-by: Lijo Lazar <lijo.lazar at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 46af07faf8c8..ae83e23872fa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -6187,8 +6187,8 @@ static void amdgpu_device_gpu_bandwidth(struct amdgpu_device *adev,
 		}
 	} else {
 		/* use the device itself */
-		*speed = pcie_get_speed_cap(parent);
-		*width = pcie_get_width_cap(parent);
+		*speed = pcie_get_speed_cap(adev->pdev);
+		*width = pcie_get_width_cap(adev->pdev);
 	}
 }
 
-- 
2.34.1