drm/amd/display: Fixed dim around 1sec when resume from S3 (v2)

root cause:
DMCU try to perform a smoothness brightness change.Incorrect initial
brightness level causes the 1 sec dim.
Change:
Cache brightness level in stream, and clear it when edp backlight on.
If brightness level in stream is 0, set brightness with ramp value is 0.
DMCU will set the brightness without smoothness transition.

v2: squash in null pointer fix (Harry)
Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -1960,6 +1960,13 @@ bool dc_link_set_backlight_level(const struct dc_link *link, uint32_t level,
 		(abm->funcs->set_backlight_level == NULL))
 		return false;
 
+	if (stream) {
+		if (stream->bl_pwm_level == 0)
+			frame_ramp = 0;
+
+		((struct dc_stream_state *)stream)->bl_pwm_level = level;
+	}
+
 	use_smooth_brightness = dmcu->funcs->is_dmcu_initialized(dmcu);
 
 	DC_LOG_BACKLIGHT("New Backlight level: %d (0x%X)\n", level, level);

drivers/gpu/drm/amd/display/dc/dc_stream.h

@@ -78,6 +78,7 @@ struct dc_stream_state {
 
 	/* DMCU info */
 	unsigned int abm_level;
+	unsigned int bl_pwm_level;
 
 	/* from core_stream struct */
 	struct dc_context *ctx;

drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c

@@ -1006,8 +1006,10 @@ void dce110_unblank_stream(struct pipe_ctx *pipe_ctx,
 	if (dc_is_dp_signal(pipe_ctx->stream->signal))
 		pipe_ctx->stream_res.stream_enc->funcs->dp_unblank(pipe_ctx->stream_res.stream_enc, &params);
 
-	if (link->local_sink && link->local_sink->sink_signal == SIGNAL_TYPE_EDP)
+	if (link->local_sink && link->local_sink->sink_signal == SIGNAL_TYPE_EDP) {
 		link->dc->hwss.edp_backlight_control(link, true);
+		stream->bl_pwm_level = 0;
+	}
 }
 void dce110_blank_stream(struct pipe_ctx *pipe_ctx)
 {