[PATCH] usb: gadget: u_ether: Fix host MAC address case

["Konrad Gräfe" <k.graefe@gateware.de>]

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As the CDC-ECM specification states the host MAC address must be sent to
the host as an uppercase hexadecimal string:
     The Unicode character is chosen from the set of values 30h through
     39h and 41h through 46h (0-9 and A-F).

However, snprintf(.., "%pm", ..) generates a lowercase MAC address
string. While most host drivers are tolerant to this, UsbNcm.sys on
Windows 10 is not. Instead it uses a different MAC address with all
bytes set to zero including and after the first byte containing a
lowercase letter. On Windows 11 Microsoft fixed it, but apparently they
did not backport the fix.

This change fixes the issue by upper-casing the MAC to comply with the
specification.

Signed-off-by: Konrad Gräfe <k.graefe@gateware.de>
---
  drivers/usb/gadget/function/u_ether.c | 9 ++++++++-
  1 file changed, 8 insertions(+), 1 deletion(-)


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diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index 6956ad8ba8dd..250734e090fc 100644
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -958,6 +958,7 @@ EXPORT_SYMBOL_GPL(gether_get_host_addr);
 int gether_get_host_addr_cdc(struct net_device *net, char *host_addr, int len)
 {
 	struct eth_dev *dev;
+	int i, slen;
 
 	if (len < 13)
 		return -EINVAL;
@@ -965,7 +966,13 @@ int gether_get_host_addr_cdc(struct net_device *net, char *host_addr, int len)
 	dev = netdev_priv(net);
 	snprintf(host_addr, len, "%pm", dev->host_mac);
 
-	return strlen(host_addr);
+
+	slen = strlen(host_addr);
+
+	for (i = 0; i < slen; i++)
+		host_addr[i] = toupper(host_addr[i]);
+
+	return slen;
 }
 EXPORT_SYMBOL_GPL(gether_get_host_addr_cdc);