soundwire: intel: refine runtime pm for SDW_INTEL_CLK_STOP_BUS_RESET

When all the links are suspended, the HDaudio controller may suspend
and the power rails to the SoundWire IP may be disabled, requiring a
complete re-initialization/enumeration on resume. However, if one or
more Masters remained active, the HDaudio controller will remain active
and the power rails will remain enabled. As a result, during the link
resume step we can check if the context was preserved by verifying if
the clock was stopped, and avoid doing a complete bus reset and
re-enumeration.
Signed-off-by: Rander Wang <rander.wang@intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20200817152923.3259-13-yung-chuan.liao@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/intel.c

@@ -1698,6 +1698,8 @@ static int intel_resume_runtime(struct device *dev)
 	struct sdw_intel *sdw = cdns_to_intel(cdns);
 	struct sdw_bus *bus = &cdns->bus;
 	u32 clock_stop_quirks;
+	bool clock_stop0;
+	int status;
 	int ret;
 
 	if (bus->prop.hw_disabled) {
@@ -1739,11 +1741,24 @@ static int intel_resume_runtime(struct device *dev)
 			return ret;
 		}
 
+		/*
+		 * An exception condition occurs for the CLK_STOP_BUS_RESET
+		 * case if one or more masters remain active. In this condition,
+		 * all the masters are powered on for they are in the same power
+		 * domain. Master can preserve its context for clock stop0, so
+		 * there is no need to clear slave status and reset bus.
+		 */
+		clock_stop0 = sdw_cdns_is_clock_stop(&sdw->cdns);
+
 		/*
 		 * make sure all Slaves are tagged as UNATTACHED and
 		 * provide reason for reinitialization
 		 */
-		sdw_clear_slave_status(bus, SDW_UNATTACH_REQUEST_MASTER_RESET);
+		if (!clock_stop0) {
+			status = SDW_UNATTACH_REQUEST_MASTER_RESET;
+			sdw_clear_slave_status(bus, status);
+		}
+
 
 		ret = sdw_cdns_enable_interrupt(cdns, true);
 		if (ret < 0) {
@@ -1751,7 +1766,7 @@ static int intel_resume_runtime(struct device *dev)
 			return ret;
 		}
 
-		ret = sdw_cdns_clock_restart(cdns, true);
+		ret = sdw_cdns_clock_restart(cdns, !clock_stop0);
 		if (ret < 0) {
 			dev_err(dev, "unable to restart clock during resume\n");
 			return ret;