drm/amd/display: Skip unnecessary abm disable

[Why]
We try to disable abm immediately when it's being gradually
disabled, which causes backlight ramping being paused in the
middle

[How]
Don't disable abm immediately if abm has been or is being
disabled through set_abm_level path
Reviewed-by: Anthony Koo <anthony.koo@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Sherry Wang <yao.wang1@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/hwss/dcn21/dcn21_hwseq.c

@@ -183,6 +183,12 @@ void dcn21_set_abm_immediate_disable(struct pipe_ctx *pipe_ctx)
 	struct panel_cntl *panel_cntl = pipe_ctx->stream->link->panel_cntl;
 	struct dmcu *dmcu = pipe_ctx->stream->ctx->dc->res_pool->dmcu;
 
+	// make a short term w/a for an issue that backlight ramping unexpectedly paused in the middle,
+	// will decouple backlight from ABM and redefine DMUB interface, then this w/a could be removed
+	if (pipe_ctx->stream->abm_level == 0 || pipe_ctx->stream->abm_level == ABM_LEVEL_IMMEDIATE_DISABLE) {
+		return;
+	}
+
 	if (dmcu) {
 		dce110_set_abm_immediate_disable(pipe_ctx);
 		return;