ASoC: Intel: Skylake: Shield against no-NHLT configurations

Some configurations expose no NHLT table at all within their
/sys/firmware/acpi/tables. To prevent NULL-dereference errors from
occurring, adjust probe flow and append additional safety checks in
functions involved in NHLT lifecycle.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200305145314.32579-5-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/intel/skylake/skl-nhlt.c

@@ -182,7 +182,8 @@ void skl_nhlt_remove_sysfs(struct skl_dev *skl)
 {
 	struct device *dev = &skl->pci->dev;
 
-	sysfs_remove_file(&dev->kobj, &dev_attr_platform_id.attr);
+	if (skl->nhlt)
+		sysfs_remove_file(&dev->kobj, &dev_attr_platform_id.attr);
 }
 
 /*

sound/soc/intel/skylake/skl.c

@@ -633,6 +633,9 @@ static int skl_clock_device_register(struct skl_dev *skl)
 	struct platform_device_info pdevinfo = {NULL};
 	struct skl_clk_pdata *clk_pdata;
 
+	if (!skl->nhlt)
+		return 0;
+
 	clk_pdata = devm_kzalloc(&skl->pci->dev, sizeof(*clk_pdata),
 							GFP_KERNEL);
 	if (!clk_pdata)
@@ -1074,7 +1077,8 @@ out_dsp_free:
 out_clk_free:
 	skl_clock_device_unregister(skl);
 out_nhlt_free:
-	intel_nhlt_free(skl->nhlt);
+	if (skl->nhlt)
+		intel_nhlt_free(skl->nhlt);
 out_free:
 	skl_free(bus);
 
@@ -1123,7 +1127,8 @@ static void skl_remove(struct pci_dev *pci)
 	skl_dmic_device_unregister(skl);
 	skl_clock_device_unregister(skl);
 	skl_nhlt_remove_sysfs(skl);
-	intel_nhlt_free(skl->nhlt);
+	if (skl->nhlt)
+		intel_nhlt_free(skl->nhlt);
 	skl_free(bus);
 	dev_set_drvdata(&pci->dev, NULL);
 }