From 8e48d0df6b5a249e4f9f0759cc55a45af186b564 Mon Sep 17 00:00:00 2001
From: Michael Brown <mcb30@ipxe.org>
Date: Mon, 3 Jul 2017 13:38:55 +0100
Subject: [PATCH] [usb] Use non-zero language ID to retrieve strings

We currently use a zero language ID to retrieve strings such as the
ECM/NCM MAC address.  This works on most hardware devices, but is
known to fail on some software emulated CDC-NCM devices.

Fix by using the first supported language ID, falling back to English
(0x0409) if any error occurs when fetching the list of supported
languages.  This matches the behaviour of the Linux kernel.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/drivers/bus/usb.c  | 37 ++++++++++++++++++++++++++++++++++++-
 src/include/ipxe/usb.h |  6 ++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/src/drivers/bus/usb.c b/src/drivers/bus/usb.c
index bd2a446b..d8db3849 100644
--- a/src/drivers/bus/usb.c
+++ b/src/drivers/bus/usb.c
@@ -843,12 +843,40 @@ int usb_control ( struct usb_device *usb, unsigned int request,
 	return rc;
 }
 
+/**
+ * Get default language ID
+ *
+ * @v usb		USB device
+ * @ret language	Language ID
+ */
+static unsigned int usb_get_default_language ( struct usb_device *usb ) {
+	struct {
+		struct usb_descriptor_header header;
+		uint16_t language[1];
+	} __attribute__ (( packed )) desc;
+	unsigned int language;
+	int rc;
+
+	/* Get descriptor */
+	if ( ( rc = usb_get_descriptor ( usb, 0, USB_STRING_DESCRIPTOR, 0, 0,
+					 &desc.header, sizeof ( desc ) ) ) !=0){
+		DBGC ( usb, "USB %s has no default language: %s\n",
+		       usb->name, strerror ( rc ) );
+		return USB_LANG_ENGLISH;
+	}
+
+	/* Use first language ID */
+	language = le16_to_cpu ( desc.language[0] );
+	DBGC2 ( usb, "USB %s default language %#04x\n", usb->name, language );
+	return language;
+}
+
 /**
  * Get USB string descriptor
  *
  * @v usb		USB device
  * @v index		String index
- * @v language		Language ID
+ * @v language		Language ID, or 0 to use default
  * @v buf		Data buffer
  * @v len		Length of buffer
  * @ret len		String length (excluding NUL), or negative error
@@ -864,6 +892,13 @@ int usb_get_string_descriptor ( struct usb_device *usb, unsigned int index,
 	unsigned int i;
 	int rc;
 
+	/* Use default language ID, if applicable */
+	if ( ( language == 0 ) && ( index != 0 ) ) {
+		if ( ! usb->language )
+			usb->language = usb_get_default_language ( usb );
+		language = usb->language;
+	}
+
 	/* Allocate buffer for string */
 	desc = malloc ( sizeof ( *desc ) );
 	if ( ! desc ) {
diff --git a/src/include/ipxe/usb.h b/src/include/ipxe/usb.h
index e7909d30..68289d26 100644
--- a/src/include/ipxe/usb.h
+++ b/src/include/ipxe/usb.h
@@ -223,6 +223,9 @@ struct usb_string_descriptor {
 /** A USB string descriptor */
 #define USB_STRING_DESCRIPTOR 3
 
+/** Language ID for English */
+#define USB_LANG_ENGLISH 0x0409
+
 /** A USB interface descriptor */
 struct usb_interface_descriptor {
 	/** Descriptor header */
@@ -728,6 +731,9 @@ struct usb_device {
 	struct usb_endpoint control;
 	/** Completed control transfers */
 	struct list_head complete;
+
+	/** Default language ID (if known) */
+	unsigned int language;
 };
 
 /** USB device host controller operations */