drm/amdgpu/discovery: add comments about VCN instance handling

Add comments to clarify code that is safe, but triggers and
smatch warning.

Link: https://lists.freedesktop.org/archives/amd-gfx/2022-June/079905.html
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
index 91f21b7..b081128 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
@@ -1435,6 +1435,11 @@ static int amdgpu_discovery_get_vcn_info(struct amdgpu_device *adev)
                return -EINVAL;
        }
 
+       /* num_vcn_inst is currently limited to AMDGPU_MAX_VCN_INSTANCES
+        * which is smaller than VCN_INFO_TABLE_MAX_NUM_INSTANCES
+        * but that may change in the future with new GPUs so keep this
+        * check for defensive purposes.
+        */
        if (adev->vcn.num_vcn_inst > VCN_INFO_TABLE_MAX_NUM_INSTANCES) {
                dev_err(adev->dev, "invalid vcn instances\n");
                return -EINVAL;
@@ -1450,6 +1455,9 @@ static int amdgpu_discovery_get_vcn_info(struct amdgpu_device *adev)
 
        switch (le16_to_cpu(vcn_info->v1.header.version_major)) {
        case 1:
+               /* num_vcn_inst is currently limited to AMDGPU_MAX_VCN_INSTANCES
+                * so this won't overflow.
+                */
                for (v = 0; v < adev->vcn.num_vcn_inst; v++) {
                        adev->vcn.vcn_codec_disable_mask[v] =
                                le32_to_cpu(vcn_info->v1.instance_info[v].fuse_data.all_bits);