ASoC: SOF: pci: change the default firmware path when the community key is used

Since ApolloLake, Intel platforms require signed firmware. On all
Windows platforms the default is to require the Intel production key
be used. But some platforms allow for a community key to be used,
which allows developers to compile/build their own firmware.

In the linux-firmware tree, the default intel/sof path is used for
firmwares signed for the production key, and files signed with the
community key are located in intel/sof/community.

Since we don't have an API to query which key is used on what
platforms, we have to rely on DMI-based quirks.

Developers can bypass this mechanism by setting a kernel 'fw_path'
module parameter. Additional dynamic debug traces are provided to help
debug cases where the wrong file might be used.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200107160840.1524-2-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

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

@@ -9,6 +9,7 @@
 //
 
 #include <linux/firmware.h>
+#include <linux/dmi.h>
 #include <linux/module.h>
 #include <linux/pci.h>
 #include <linux/pm_runtime.h>
@@ -36,6 +37,23 @@ MODULE_PARM_DESC(sof_pci_debug, "SOF PCI debug options (0x0 all off)");
 
 #define SOF_PCI_DISABLE_PM_RUNTIME BIT(0)
 
+static const struct dmi_system_id community_key_platforms[] = {
+	{
+		.ident = "Up Squared",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "AAEON"),
+			DMI_MATCH(DMI_BOARD_NAME, "UP-APL01"),
+		}
+	},
+	{
+		.ident = "Google Chromebooks",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Google"),
+		}
+	},
+	{},
+};
+
 #if IS_ENABLED(CONFIG_SND_SOC_SOF_APOLLOLAKE)
 static const struct sof_dev_desc bxt_desc = {
 	.machines		= snd_soc_acpi_intel_bxt_machines,
@@ -290,12 +308,34 @@ static int sof_pci_probe(struct pci_dev *pci,
 	sof_pdata->dev = dev;
 	sof_pdata->fw_filename = desc->default_fw_filename;
 
+	/*
+	 * for platforms using the SOF community key, change the
+	 * default path automatically to pick the right files from the
+	 * linux-firmware tree. This can be overridden with the
+	 * fw_path kernel parameter, e.g. for developers.
+	 */
+
 	/* alternate fw and tplg filenames ? */
-	if (fw_path)
+	if (fw_path) {
 		sof_pdata->fw_filename_prefix = fw_path;
-	else
+
+		dev_dbg(dev,
+			"Module parameter used, changed fw path to %s\n",
+			sof_pdata->fw_filename_prefix);
+
+	} else if (dmi_check_system(community_key_platforms)) {
+		sof_pdata->fw_filename_prefix =
+			devm_kasprintf(dev, GFP_KERNEL, "%s/%s",
+				       sof_pdata->desc->default_fw_path,
+				       "community");
+
+		dev_dbg(dev,
+			"Platform uses community key, changed fw path to %s\n",
+			sof_pdata->fw_filename_prefix);
+	} else {
 		sof_pdata->fw_filename_prefix =
 			sof_pdata->desc->default_fw_path;
+	}
 
 	if (tplg_path)
 		sof_pdata->tplg_filename_prefix = tplg_path;