soundwire: intel: pm_runtime idle scheduling

Add quirk and pm_runtime idle scheduling to let the Master suspend if
no Slaves become attached. This can happen when a link is not marked
as disabled and has devices exposed in the DSDT, if the power is
controlled by sideband means or the link includes a pluggable
connector.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Rander Wang <rander.wang@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20200817152923.3259-7-yung-chuan.liao@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/intel.c

@@ -31,8 +31,9 @@
  * flags reused in each byte, with master0 using the ls-byte, etc.
  */
 
-#define SDW_INTEL_MASTER_DISABLE_PM_RUNTIME BIT(0)
-#define SDW_INTEL_MASTER_DISABLE_CLOCK_STOP BIT(1)
+#define SDW_INTEL_MASTER_DISABLE_PM_RUNTIME		BIT(0)
+#define SDW_INTEL_MASTER_DISABLE_CLOCK_STOP		BIT(1)
+#define SDW_INTEL_MASTER_DISABLE_PM_RUNTIME_IDLE	BIT(2)
 
 static int md_flags;
 module_param_named(sdw_md_flags, md_flags, int, 0444);
@@ -1422,6 +1423,22 @@ int intel_master_startup(struct platform_device *pdev)
 		pm_runtime_enable(dev);
 	}
 
+	/*
+	 * The runtime PM status of Slave devices is "Unsupported"
+	 * until they report as ATTACHED. If they don't, e.g. because
+	 * there are no Slave devices populated or if the power-on is
+	 * delayed or dependent on a power switch, the Master will
+	 * remain active and prevent its parent from suspending.
+	 *
+	 * Conditionally force the pm_runtime core to re-evaluate the
+	 * Master status in the absence of any Slave activity. A quirk
+	 * is provided to e.g. deal with Slaves that may be powered on
+	 * with a delay. A more complete solution would require the
+	 * definition of Master properties.
+	 */
+	if (!(link_flags & SDW_INTEL_MASTER_DISABLE_PM_RUNTIME_IDLE))
+		pm_runtime_idle(dev);
+
 	return 0;
 
 err_interrupt:
@@ -1561,6 +1578,7 @@ static int intel_resume(struct device *dev)
 	struct sdw_cdns *cdns = dev_get_drvdata(dev);
 	struct sdw_intel *sdw = cdns_to_intel(cdns);
 	struct sdw_bus *bus = &cdns->bus;
+	int link_flags;
 	int ret;
 
 	if (bus->prop.hw_disabled) {
@@ -1577,6 +1595,10 @@ static int intel_resume(struct device *dev)
 		pm_runtime_set_active(dev);
 		pm_runtime_mark_last_busy(dev);
 		pm_runtime_enable(dev);
+
+		link_flags = md_flags >> (bus->link_id * 8);
+		if (!(link_flags & SDW_INTEL_MASTER_DISABLE_PM_RUNTIME_IDLE))
+			pm_runtime_idle(dev);
 	}
 
 	ret = intel_init(sdw);