diff --git a/llvm/docs/AMDGPUUsage.rst b/llvm/docs/AMDGPUUsage.rst
--- a/llvm/docs/AMDGPUUsage.rst
+++ b/llvm/docs/AMDGPUUsage.rst
@@ -1196,6 +1196,8 @@
                                      uniform control flow.
 
      ``amdgpu_cs_chain_preserve``    Same as ``amdgpu_cs_chain``, but active lanes for VGPRs starting at v8 are preserved.
+                                     Calls to ``amdgpu_gfx`` functions are not allowed, and any calls to ``llvm.amdgcn.cs.chain``
+                                     must not pass more VGPR arguments than the caller's VGPR function parameters.
 
      ``amdgpu_es``                   Used for AMDPAL shader stage before geometry shader if geometry is in
                                      use. So either the domain (= tessellation evaluation) shader if