soundwire: intel: exit clock stop mode on system suspend

Intel validation reported an issue where the HW_RST self-clearing bit
is not cleared in hardware, which as a ripple effect creates issues
with the clock stop mode.

This happens is a specific sequence where the Intel manager is
pm_runtime suspended with the clock-stop mode enabled. During the
system suspend, we currently do nothing, which can lead to potential
issues on system resume and the following pm_runtime suspend,
depending on the hardware state.

This patch suggests a full resume (parent+child devices) if the
clock-stop mode is used. This may require extra time but will make the
suspend/resume flows completely symmetric. This also removes a race
condition where we could not access SHIM registers if the parent was
suspended as well. Resuming the link also resumes the parent by
construction.

BugLink: #2606
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Bard Liao <bard.liao@intel.com>

drivers/soundwire/intel.c

@@ -1527,6 +1527,70 @@ int intel_link_process_wakeen_event(struct auxiliary_device *auxdev)
  * PM calls
  */
 
+static int intel_resume_child_device(struct device *dev, void *data)
+{
+	int ret;
+	struct sdw_slave *slave = dev_to_sdw_dev(dev);
+
+	if (!slave->probed) {
+		dev_dbg(dev, "%s: skipping device, no probed driver\n", __func__);
+		return 0;
+	}
+	if (!slave->dev_num_sticky) {
+		dev_dbg(dev, "%s: skipping device, never detected on bus\n", __func__);
+		return 0;
+	}
+
+	ret = pm_request_resume(dev);
+	if (ret < 0)
+		dev_err(dev, "%s: pm_request_resume failed: %d\n", __func__, ret);
+
+	return ret;
+}
+
+static int __maybe_unused intel_pm_prepare(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;
+	u32 clock_stop_quirks;
+	int ret = 0;
+
+	if (bus->prop.hw_disabled || !sdw->startup_done) {
+		dev_dbg(dev, "SoundWire master %d is disabled or not-started, ignoring\n",
+			bus->link_id);
+		return 0;
+	}
+
+	clock_stop_quirks = sdw->link_res->clock_stop_quirks;
+
+	if ((clock_stop_quirks & SDW_INTEL_CLK_STOP_BUS_RESET) ||
+	    !clock_stop_quirks) {
+		/*
+		 * Try to resume the entire bus (parent + child devices) to exit
+		 * the clock stop mode. If this fails, we keep going since we don't want
+		 * to prevent system suspend from happening and errors should be recoverable
+		 * on resume.
+		 */
+		ret = device_for_each_child(bus->dev, NULL, intel_resume_child_device);
+
+		if (ret < 0)
+			dev_err(dev, "%s: intel_resume_child_device failed: %d\n", __func__, ret);
+
+		/*
+		 * in the case where a link was started but does not have anything connected,
+		 * we still need to resume to keep link power up/down sequences balanced.
+		 * This is a no-op if a child device was present, since resuming the child
+		 * device would also resume the parent
+		 */
+		ret = pm_request_resume(dev);
+		if (ret < 0)
+			dev_err(dev, "%s: pm_request_resume failed: %d\n", __func__, ret);
+	}
+
+	return 0;
+}
+
 static int __maybe_unused intel_suspend(struct device *dev)
 {
 	struct sdw_cdns *cdns = dev_get_drvdata(dev);
@@ -1923,6 +1987,7 @@ static int __maybe_unused intel_resume_runtime(struct device *dev)
 }
 
 static const struct dev_pm_ops intel_pm = {
+	.prepare = intel_pm_prepare,
 	SET_SYSTEM_SLEEP_PM_OPS(intel_suspend, intel_resume)
 	SET_RUNTIME_PM_OPS(intel_suspend_runtime, intel_resume_runtime, NULL)
 };