drm/amd/display: Add null check for pipe_ctx->plane_state in dcn20_program_pipe

This commit addresses a null pointer dereference issue in the
`dcn20_program_pipe` function. The issue could occur when
`pipe_ctx->plane_state` is null.

The fix adds a check to ensure `pipe_ctx->plane_state` is not null
before accessing. This prevents a null pointer dereference.

Reported by smatch:
drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn20/dcn20_hwseq.c:1925 dcn20_program_pipe() error: we previously assumed 'pipe_ctx->plane_state' could be null (see line 1877)

Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c

@@ -1922,22 +1922,29 @@ static void dcn20_program_pipe(
 				dc->res_pool->hubbub, pipe_ctx->plane_res.hubp->inst, pipe_ctx->hubp_regs.det_size);
 	}
 
-	if (pipe_ctx->update_flags.raw || pipe_ctx->plane_state->update_flags.raw || pipe_ctx->stream->update_flags.raw)
+	if (pipe_ctx->update_flags.raw ||
+	    (pipe_ctx->plane_state && pipe_ctx->plane_state->update_flags.raw) ||
+	    pipe_ctx->stream->update_flags.raw)
 		dcn20_update_dchubp_dpp(dc, pipe_ctx, context);
 
-	if (pipe_ctx->update_flags.bits.enable
-			|| pipe_ctx->plane_state->update_flags.bits.hdr_mult)
+	if (pipe_ctx->update_flags.bits.enable ||
+	    (pipe_ctx->plane_state && pipe_ctx->plane_state->update_flags.bits.hdr_mult))
 		hws->funcs.set_hdr_multiplier(pipe_ctx);
 
 	if (hws->funcs.populate_mcm_luts) {
-		hws->funcs.populate_mcm_luts(dc, pipe_ctx, pipe_ctx->plane_state->mcm_luts,
-				pipe_ctx->plane_state->lut_bank_a);
-		pipe_ctx->plane_state->lut_bank_a = !pipe_ctx->plane_state->lut_bank_a;
+		if (pipe_ctx->plane_state) {
+			hws->funcs.populate_mcm_luts(dc, pipe_ctx, pipe_ctx->plane_state->mcm_luts,
+						     pipe_ctx->plane_state->lut_bank_a);
+			pipe_ctx->plane_state->lut_bank_a = !pipe_ctx->plane_state->lut_bank_a;
+		}
 	}
 	if (pipe_ctx->update_flags.bits.enable ||
-	    pipe_ctx->plane_state->update_flags.bits.in_transfer_func_change ||
-	    pipe_ctx->plane_state->update_flags.bits.gamma_change ||
-	    pipe_ctx->plane_state->update_flags.bits.lut_3d)
+	    (pipe_ctx->plane_state &&
+	     pipe_ctx->plane_state->update_flags.bits.in_transfer_func_change) ||
+	    (pipe_ctx->plane_state &&
+	     pipe_ctx->plane_state->update_flags.bits.gamma_change) ||
+	    (pipe_ctx->plane_state &&
+	     pipe_ctx->plane_state->update_flags.bits.lut_3d))
 		hws->funcs.set_input_transfer_func(dc, pipe_ctx, pipe_ctx->plane_state);
 
 	/* dcn10_translate_regamma_to_hw_format takes 750us to finish
@@ -1947,7 +1954,8 @@ static void dcn20_program_pipe(
 	if (pipe_ctx->update_flags.bits.enable ||
 			pipe_ctx->update_flags.bits.plane_changed ||
 			pipe_ctx->stream->update_flags.bits.out_tf ||
-			pipe_ctx->plane_state->update_flags.bits.output_tf_change)
+			(pipe_ctx->plane_state &&
+			 pipe_ctx->plane_state->update_flags.bits.output_tf_change))
 		hws->funcs.set_output_transfer_func(dc, pipe_ctx, pipe_ctx->stream);
 
 	/* If the pipe has been enabled or has a different opp, we
@@ -1971,7 +1979,7 @@ static void dcn20_program_pipe(
 	}
 
 	/* Set ABM pipe after other pipe configurations done */
-	if (pipe_ctx->plane_state->visible) {
+	if ((pipe_ctx->plane_state && pipe_ctx->plane_state->visible)) {
 		if (pipe_ctx->stream_res.abm) {
 			dc->hwss.set_pipe(pipe_ctx);
 			pipe_ctx->stream_res.abm->funcs->set_abm_level(pipe_ctx->stream_res.abm,