From: Foster Snowhill Date: Sat, 25 Jan 2025 23:54:09 +0000 (+0100) Subject: usbnet: ipheth: document scope of NCM implementation X-Git-Tag: v6.14-rc1~33^2~15^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=be154b598fa54136e2be17d6dd13c8a8bc0078ce;p=thirdparty%2Flinux.git usbnet: ipheth: document scope of NCM implementation Clarify that the "NCM" implementation in `ipheth` is very limited, as iOS devices aren't compatible with the CDC NCM specification in regular tethering mode. For a standards-compliant implementation, one shall turn to the `cdc_ncm` module. Cc: stable@vger.kernel.org # 6.5.x Signed-off-by: Foster Snowhill Reviewed-by: Jakub Kicinski Signed-off-by: Paolo Abeni --- diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c index 5347cd7e295b3..a19789b571905 100644 --- a/drivers/net/usb/ipheth.c +++ b/drivers/net/usb/ipheth.c @@ -218,6 +218,14 @@ static int ipheth_rcvbulk_callback_legacy(struct urb *urb) return ipheth_consume_skb(buf, len, dev); } +/* In "NCM mode", the iOS device encapsulates RX (phone->computer) traffic + * in NCM Transfer Blocks (similarly to CDC NCM). However, unlike reverse + * tethering (handled by the `cdc_ncm` driver), regular tethering is not + * compliant with the CDC NCM spec, as the device is missing the necessary + * descriptors, and TX (computer->phone) traffic is not encapsulated + * at all. Thus `ipheth` implements a very limited subset of the spec with + * the sole purpose of parsing RX URBs. + */ static int ipheth_rcvbulk_callback_ncm(struct urb *urb) { struct usb_cdc_ncm_nth16 *ncmh;