[bug report] drm/amd/display: Register DCN as a PMFW DF C-state client on DCN42

[Dan Carpenter <error27@gmail.com>]

Hello Leo Chen,

Commit 53845307d52e ("drm/amd/display: Register DCN as a PMFW DF
C-state client on DCN42") from Jul 9, 2026, leads to the following
Smatch complaint:

    drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn42/dcn42_hwseq.c:686 dcn42_prepare_bandwidth()
    warn: variable dereferenced before check 'dc->clk_mgr' (see line 681)

drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn42/dcn42_hwseq.c
   680	
   681		dcn401_prepare_bandwidth(dc, context);
                                         ^^
dc->clk_mgr is dereferenced here.

   682	
   683		/* valid C-state watermarks have now been committed to HW, so it
   684		 * is safe to vote "allow" to PMFW.
   685		 */
   686		if (dc->clk_mgr && dc->clk_mgr->funcs && dc->clk_mgr->funcs->notify_cstate_disable)
                    ^^^^^^^^^^^
so this check is too late.

   687			dc->clk_mgr->funcs->notify_cstate_disable(dc->clk_mgr, false);
   688	}

This email is a free service from the Smatch-CI project [smatch.sf.net].

regards,
dan carpenter