ASoC: SOF: pci: add debug module param

Add debug parameter for snd-sof-pci.

One of the usages for this debug parameter to disable pm_runtime,
which can be useful for platform bringup, or keep the parent device
active while enabling pm_runtime for child devices (e.g. with
SoundWire or MFD). This can also be useful to measure suspend-resume
latencies or child devices.
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191008164443.1358-5-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/sof-pci-dev.c

@@ -29,6 +29,12 @@ static char *tplg_path;
 module_param(tplg_path, charp, 0444);
 MODULE_PARM_DESC(tplg_path, "alternate path for SOF topology.");
 
+static int sof_pci_debug;
+module_param_named(sof_pci_debug, sof_pci_debug, int, 0444);
+MODULE_PARM_DESC(sof_pci_debug, "SOF PCI debug options (0x0 all off)");
+
+#define SOF_PCI_DISABLE_PM_RUNTIME BIT(0)
+
 #if IS_ENABLED(CONFIG_SND_SOC_SOF_APOLLOLAKE)
 static const struct sof_dev_desc bxt_desc = {
 	.machines		= snd_soc_acpi_intel_bxt_machines,
@@ -249,6 +255,9 @@ static void sof_pci_probe_complete(struct device *dev)
 {
 	dev_dbg(dev, "Completing SOF PCI probe");
 
+	if (sof_pci_debug & SOF_PCI_DISABLE_PM_RUNTIME)
+		return;
+
 	/* allow runtime_pm */
 	pm_runtime_set_autosuspend_delay(dev, SND_SOF_SUSPEND_DELAY_MS);
 	pm_runtime_use_autosuspend(dev);
@@ -370,7 +379,8 @@ static void sof_pci_remove(struct pci_dev *pci)
 	snd_sof_device_remove(&pci->dev);
 
 	/* follow recommendation in pci-driver.c to increment usage counter */
-	pm_runtime_get_noresume(&pci->dev);
+	if (!(sof_pci_debug & SOF_PCI_DISABLE_PM_RUNTIME))
+		pm_runtime_get_noresume(&pci->dev);
 
 	/* release pci regions and disable device */
 	pci_release_regions(pci);