[PATCH v3] 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.koe...@amd.com>
Cc: Alex Deucher <alexander.deuc...@amd.com>
Reported-by: Dan Carpenter <dan.carpen...@linaro.org>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com>
Suggested-by: Lijo Lazar <lijo.la...@amd.com>
---
v3: change the else s/parent/adev->pdev (Lijo)

 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 46af07faf8c8..8ed7f2f8546d 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -6174,7 +6174,7 @@ static void amdgpu_device_gpu_bandwidth(struct 
amdgpu_device *adev,
                return;
 
        parent = pci_upstream_bridge(parent);
-       if (parent && parent->vendor == PCI_VENDOR_ID_ATI) {
+       if (parent->vendor == PCI_VENDOR_ID_ATI) {
                /* use the upstream/downstream switches internal to dGPU */
                *speed = pcie_get_speed_cap(parent);
                *width = pcie_get_width_cap(parent);
@@ -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