[PATCH v2] drm/amdgpu: Avoid possible buffer overflow

[Su Hui]

smatch error:
drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1257 
amdgpu_discovery_reg_base_init() error:
testing array offset 'adev->vcn.num_vcn_inst' after use.

change the assignment order to avoid buffer overflow.

Fixes: c40bdfb2ffa4 ("drm/amdgpu: fix incorrect VCN revision in SRIOV")
Signed-off-by: Su Hui <su...@nfschina.com>
---
changes in v2:
 - fix the error about ip->revision (thanks to Christophe JAILLET).
 drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
index 8e1cfc87122d..b07bfd106a9b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
@@ -1250,11 +1250,10 @@ static int amdgpu_discovery_reg_base_init(struct 
amdgpu_device *adev)
                                 *     0b10 : encode is disabled
                                 *     0b01 : decode is disabled
                                 */
-                               adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
-                                       ip->revision & 0xc0;
-                               ip->revision &= ~0xc0;
                                if (adev->vcn.num_vcn_inst <
                                    AMDGPU_MAX_VCN_INSTANCES) {
+                                       
adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
+                                               ip->revision & 0xc0;
                                        adev->vcn.num_vcn_inst++;
                                        adev->vcn.inst_mask |=
                                                (1U << ip->instance_number);
@@ -1265,6 +1264,7 @@ static int amdgpu_discovery_reg_base_init(struct 
amdgpu_device *adev)
                                                adev->vcn.num_vcn_inst + 1,
                                                AMDGPU_MAX_VCN_INSTANCES);
                                }
+                               ip->revision &= ~0xc0;
                        }
                        if (le16_to_cpu(ip->hw_id) == SDMA0_HWID ||
                            le16_to_cpu(ip->hw_id) == SDMA1_HWID ||
-- 
2.30.2