[bug report] drm/amd/display: Refactor SubVP cursor limiting logic

[Dan Carpenter]

Hello Dillon Varone,

Commit 4465dd0e41e8 ("drm/amd/display: Refactor SubVP cursor limiting
logic") from Apr 1, 2025 (linux-next), leads to the following Smatch
static checker warning:

	drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c:336 dc_stream_program_cursor_attributes()
	error: we previously assumed 'stream' could be null (see line 334)

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c
    327 bool dc_stream_program_cursor_attributes(
    328         struct dc_stream_state *stream,
    329         const struct dc_cursor_attributes *attributes)
    330 {
    331         struct dc  *dc;
    332         bool reset_idle_optimizations = false;
    333 
    334         dc = stream ? stream->ctx->dc : NULL;
                     ^^^^^^
The old code assumed stream could be NULL.

    335 
--> 336         if (dc_stream_set_cursor_attributes(stream, attributes)) {
                                                    ^^^^^^
The refactor added an unchecked dereference.

drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_stream.c
   313  bool dc_stream_set_cursor_attributes(
   314          struct dc_stream_state *stream,
   315          const struct dc_cursor_attributes *attributes)
   316  {
   317          bool result = false;
   318  
   319          if (dc_stream_check_cursor_attributes(stream, stream->ctx->dc->current_state, attributes)) {
                                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Here.  This function used to check for if stream as NULL and return false
at the start.  Probably we should add that back.

   320                  stream->cursor_attributes = *attributes;
   321                  result = true;
   322          }
   323  
   324          return result;
   325  }

regards,
dan carpenter