[bug report] drm/i915/dp_mst: Fix configuring TUs for a disconnected stream

[Dan Carpenter <error27@gmail.com>]

Hello Imre Deak,

Commit ee00f8fbb2b2 ("drm/i915/dp_mst: Fix configuring TUs for a
disconnected stream") from Sep 7, 2026 (linux-next), leads to the
following Smatch static checker warning:

	drivers/gpu/drm/i915/display/intel_link_bw.c:69 intel_link_bw_init_limits()
	error: we previously assumed 'crtc_state' could be null (see line 67)

drivers/gpu/drm/i915/display/intel_link_bw.c
    53 void intel_link_bw_init_limits(struct intel_atomic_state *state,
    54                                struct intel_link_bw_limits *limits)
    55 {
    56         struct intel_display *display = to_intel_display(state);
    57         enum pipe pipe;
    58 
    59         limits->link_dsc_pipes = 0;
    60         limits->bpp_limit_reached_pipes = 0;
    61         for_each_pipe(display, pipe) {
    62                 struct intel_crtc *crtc = intel_crtc_for_pipe(display, pipe);
    63                 const struct intel_crtc_state *crtc_state =
    64                         intel_atomic_get_new_crtc_state(state, crtc);
    65                 int forced_bpp_x16 = get_forced_link_bpp_x16(state, crtc);
    66 
    67                 if ((state->base.duplicated && crtc_state) ||
                                                      ^^^^^^^^^^
Check for NULL

    68                     intel_dp_mst_stream_disconnected(state, crtc)) {
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Possible this also implied crtc_state is non-NULL?  It looks more like
intel_dp_mst_stream_disconnected() assumes that crtc_state is non-NULL...

--> 69                         limits->max_bpp_x16[pipe] = crtc_state->max_link_bpp_x16;
                                                           ^^^^^^^^^^^^
Unchecked dereference.

    70                         if (intel_dsc_enabled_on_link(crtc_state))
    71                                 limits->link_dsc_pipes |= BIT(pipe);
    72                 } else {
    73                         limits->max_bpp_x16[pipe] = INT_MAX;
    74                 }
    75 
    76                 if (forced_bpp_x16)
    77                         limits->max_bpp_x16[pipe] = min(limits->max_bpp_x16[pipe], forced_bpp_x16);
    78         }
    79 }

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regards,
dan carpenter