drm/amd/display: Add optional optimization for IPS handshake

[Why]
It's possible to skip parts of the eval and exit sequencing if we know
whether DCN is in IPS2 already or if it's committed to going to idle
and not in IPS2.

[How]
Skip IPS2 entry/exit if DMCUB is idle but the IPS2 commit is not set.

Skip the eval delay if DMCUB is already in IPS2 since we know we need
to exit.

These are turned off by default.
Reviewed-by: Duncan Ma <duncan.ma@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@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/dc.h

@@ -988,6 +988,7 @@ struct dc_debug_options {
 	bool psp_disabled_wa;
 	unsigned int ips2_eval_delay_us;
 	unsigned int ips2_entry_delay_us;
+	bool optimize_ips_handshake;
 	bool disable_dmub_reallow_idle;
 	bool disable_timeout;
 	bool disable_extblankadj;

drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c

@@ -1318,12 +1318,15 @@ static void dc_dmub_srv_exit_low_power_state(const struct dc *dc)
 		 */
 		dc_dmub_srv->needs_idle_wake = false;
 
-		if (prev_driver_signals.bits.allow_ips2) {
+		if (prev_driver_signals.bits.allow_ips2 &&
+		    (!dc->debug.optimize_ips_handshake ||
+		     ips_fw->signals.bits.ips2_commit || !ips_fw->signals.bits.in_idle)) {
 			DC_LOG_IPS(
 				"wait IPS2 eval (ips1_commit=%d ips2_commit=%d)",
 				ips_fw->signals.bits.ips1_commit,
 				ips_fw->signals.bits.ips2_commit);
 
+			if (!dc->debug.optimize_ips_handshake || !ips_fw->signals.bits.ips2_commit)
 				udelay(dc->debug.ips2_eval_delay_us);
 
 			if (ips_fw->signals.bits.ips2_commit) {

drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h

@@ -700,7 +700,8 @@ union dmub_shared_state_ips_fw_signals {
 	struct {
 		uint32_t ips1_commit : 1;  /**< 1 if in IPS1 */
 		uint32_t ips2_commit : 1; /**< 1 if in IPS2 */
-		uint32_t reserved_bits : 30; /**< Reversed */
+		uint32_t in_idle : 1; /**< 1 if DMCUB is in idle */
+		uint32_t reserved_bits : 29; /**< Reversed */
 	} bits;
 	uint32_t all;
 };